JP7639631B2 - Semiconductor light emitting device and method for manufacturing the same - Google Patents

Description

The present invention relates to a semiconductor light-emitting device and a method for manufacturing the semiconductor light-emitting device.

In order to stabilize the oscillation wavelength of a semiconductor laser, a distributed feedback (DFB) structure is often used.
Non-Patent Document 1 discloses an optical element in which a first-order diffraction grating is formed between an AlInGaN-based n-wave guiding layer and an n-cladding layer.

Japanese Journal of Applied Physics Vol. 45, No. 46, 2006, pp00. L1223-L1225

The object of the present invention is to provide a semiconductor light-emitting device and a method for manufacturing the semiconductor light-emitting device that can increase the coupling coefficient between the guided light and the diffraction grating.

A semiconductor light-emitting device according to one aspect of the present invention includes a first conductive type semiconductor layer, an active layer provided on the first conductive type semiconductor layer, a second conductive type semiconductor layer provided on the active layer, a waveguide layer provided in the second conductive type semiconductor layer and guiding the guided light while confining the guided light in the horizontal direction of the guided light guided through the active layer, a diffraction grating provided in the second conductive type semiconductor layer along the guided light direction, and a confinement layer provided on the waveguide layer and the diffraction grating and confining the guided light guided through the active layer in the vertical direction.

This makes it possible to confine the guided light in the active layer in both the horizontal and vertical directions while placing the diffraction grating close to the active layer. This makes it possible to increase the coupling coefficient between the guided light and the diffraction grating while suppressing a decrease in the light emission efficiency, and to stabilize the oscillation wavelength while suppressing a decrease in the output of the semiconductor light emitting element.

In addition, in a semiconductor light-emitting device according to one aspect of the present invention, the confinement layer is a second conductivity type semiconductor layer having a smaller refractive index than the waveguide layer.

This makes it possible to vertically confine the guided light that is guided through the active layer while suppressing mismatch between the lattice constant of the confinement layer and the lattice constant of the waveguide layer, thereby suppressing a decrease in the light emission efficiency and a decrease in the reliability of the semiconductor light emitting device.

In addition, in a semiconductor light-emitting device according to one aspect of the present invention, the confinement layer is a transparent conductive layer that is transparent to the guided light that is guided through the active layer.

This makes it possible to confine the perpendicular transverse mode perpendicular to the waveguide direction (resonator direction) of the guided light in the transparent conductive layer while suppressing the thickening of the second conductive type semiconductor layer. In addition, it is not necessary to provide a contact layer on the transparent conductive layer to make contact with the electrode, and the resistance of the current injected into the active layer via the transparent conductive layer can be reduced. This makes it possible to reduce heat generation in the semiconductor light emitting element, reduce optical loss during light propagation, and improve slope efficiency.

In addition, in a semiconductor light-emitting device according to one aspect of the present invention, the confinement layer is used as at least one of a guide layer or a cladding layer on the active layer.

This makes it possible to confine the perpendicular transverse mode during light propagation while placing the diffraction grating close to the active layer. As a result, it is possible to improve the light emission efficiency while stabilizing the oscillation wavelength.

In addition, according to a semiconductor light-emitting device according to one aspect of the present invention, the diffraction grating includes a resistive layer that is located in a portion of the second conductive type semiconductor layer and has a smaller refractive index and a larger resistance than the second conductive type semiconductor layer.

This makes it possible to provide a DFB structure on the active layer while constricting the current injected into the active layer with the resistive layer, and to increase the refractive index difference between the second conductive type semiconductor layer and the diffraction grating while suppressing the increase in crystal defects in the second conductive type semiconductor layer. This makes it possible to efficiently inject current into the light-emitting region while confining the horizontal transverse mode in the horizontal direction to the light propagation direction. Furthermore, it is possible to increase the coupling coefficient between the guided light and the diffraction grating. This makes it possible to reduce heat generation from the semiconductor light-emitting element, increase the output of the semiconductor light-emitting element, and stabilize the oscillation wavelength.

In addition, in a semiconductor light-emitting device according to one aspect of the present invention, the diffraction grating is located on both sides of the waveguide layer.

This makes it possible to ensure a refractive index difference between the second conductive type semiconductor layer and the diffraction grating. It also makes it possible to laterally confine the guided light that is guided through the active layer while locating the diffraction grating close to the active layer. This makes it possible to increase the coupling coefficient between the guided light and the diffraction grating while ensuring the reliability of the semiconductor light emitting element, thereby stabilizing the oscillation wavelength.

In addition, in a semiconductor light-emitting device according to one aspect of the present invention, the resistive layer includes a first resistive layer in which the diffraction grating is formed on both sides of a first opening in which the waveguide layer is embedded, and a second resistive layer stacked on the first resistive layer and in which a second opening in which the waveguide layer is embedded is formed.

This makes it possible to laterally confine the guided light in the active layer while arranging the diffraction grating close to the active layer, while suppressing an increase in crystal defects in the second conductive type semiconductor layer, while ensuring the refractive index difference between the second conductive type semiconductor layer and the diffraction grating, and constricting the current injected into the active layer. Therefore, it is possible to increase the coupling coefficient between the guided light and the diffraction grating while ensuring the reliability of the semiconductor light-emitting element, and it is possible to reduce the threshold current of the semiconductor light-emitting element while suppressing heat generation of the semiconductor light-emitting element. As a result, it is possible to increase the output of the semiconductor light-emitting element while suppressing deterioration of the characteristics of the semiconductor light-emitting element, and it is possible to stabilize the oscillation wavelength.

In addition, in a semiconductor light-emitting device according to one aspect of the present invention, the diffraction grating is recessed from the end face of the active layer by a distance equal to or greater than the period of the diffraction grating.

This allows a non-current injection region to be provided near the end face of the active layer, suppressing heat generation at the end face of the active layer and making it possible to protect the end face of the active layer.

In addition, according to a semiconductor light-emitting device according to one aspect of the present invention, the diffraction grating includes a phase shift portion.

This makes it possible to improve the SMSR (Side Mode Suppression Ratio) of the diffraction grating while addressing the variation in characteristics depending on the cleavage position, thereby improving the light emission efficiency of the desired oscillation wavelength.

In addition, in a semiconductor light-emitting device according to one aspect of the present invention, the length of the phase shift portion satisfies the relationship λ/(4·n _eff )·(2N-1), where N is a positive integer, n _eff is the effective refractive index of the diffraction grating, and λ is the Bragg wavelength.

This allows the phase shift section to be positioned at a position where the centers of the peaks, valleys, or peaks of the standing waves formed by the diffraction grating coincide, improving the SMSR.

In addition, in a semiconductor light-emitting device according to one aspect of the present invention, the center of the phase shift portion is located at a distance between 60% and 80% of the distance between the end face with the lower reflectance and the end face of the active layer.

As a result, even if the reflectivities of the two end faces used in the resonator are different, it is possible to improve the SMSR while lowering the threshold, and to improve the output while stabilizing the oscillation wavelength.

In addition, according to the semiconductor light-emitting device of one aspect of the present invention, when the coupling coefficient of the diffraction grating is κ and the resonator length is L, the condition 1≦κ·L≦3 is satisfied.

This makes it possible to lower the threshold value and increase the efficiency of semiconductor light-emitting devices while stabilizing the oscillation wavelength.

In addition, according to one aspect of the semiconductor light-emitting device of the present invention, the reflectance of the first end face of the active layer is set to 2% or less, and the reflectance of the second end face of the active layer is set to 90% or more.

This makes it possible to reduce the variation in the characteristics of the semiconductor light-emitting element while suppressing the decrease in light-emitting efficiency.

In addition, according to one aspect of the semiconductor light-emitting device of the present invention, the waveguide layer is made of GaN and the diffraction grating is made of AlN.

This makes it possible to realize a blue-violet laser diode, and ensures the refractive index difference between the second conductive type semiconductor layer and the diffraction grating while suppressing an increase in crystal defects in the second conductive type semiconductor layer. It also makes it possible to constrict the current injected into the active layer while suppressing an increase in thermal resistance, making it possible to suppress heat generation in the semiconductor light-emitting element. Furthermore, it makes it possible to laterally confine the guided light that is guided through the active layer, thereby increasing the output of the semiconductor light-emitting element and stabilizing the oscillation wavelength.

In addition, according to a semiconductor light-emitting device according to one aspect of the present invention, the diffraction grating has a greatest common denominator of 1 and includes multiple high-order diffraction gratings having different orders.

This allows the period of the diffraction grating to be increased while matching the diffraction conditions of the diffraction grating with the guide direction of the guided light guided through the active layer. This makes it possible to stabilize the oscillation wavelength while suppressing a decrease in oscillation efficiency. Furthermore, it is possible to realize a blue-violet laser diode with a stable oscillation wavelength while mitigating the manufacturing difficulties associated with miniaturizing the diffraction grating.

In addition, according to a semiconductor light-emitting device according to one aspect of the present invention, the multiple high-order diffraction gratings have regions in which at least one of the centers of the convex portions and the convex portions, the centers of the concave portions and the concave portions, and the centers of the convex portions and the concave portions coincide.

This increases the difference in energy density of the electric field of the standing wave formed by the high-order diffraction grating, and increases the stop band width. This increases the SMSR of the high-order diffraction grating, and increases the coupling coefficient between the guided light and the high-order diffraction grating.

In addition, according to one aspect of the semiconductor light-emitting device of the present invention, the duties of the multiple high-order diffraction gratings are different from each other.

This allows the coupling coefficient between the guided light and the high-order diffraction grating to be maximized by optimizing the unevenness pattern of the high-order diffraction grating. It also makes it possible to stabilize the oscillation wavelength while suppressing an increase in the number of steps in the manufacturing process of the semiconductor light-emitting device.

In addition, according to one aspect of the semiconductor light-emitting device of the present invention, the multiple high-order diffraction gratings are arranged so that the coupling coefficients are equal to each other.

This makes it possible to suppress a decrease in the coupling coefficient between the guided light and the high-order diffraction grating even when multiple high-order diffraction gratings are used when forming a DFB structure.

In addition, according to a method for manufacturing a semiconductor light-emitting device according to one aspect of the present invention, the method includes the steps of sequentially stacking an active layer and a second conductive type semiconductor layer on a first conductive type semiconductor layer, forming irregularities in the second conductive type semiconductor layer, stacking a resistive layer having a smaller refractive index and a larger resistance than the second conductive type semiconductor layer on the second conductive type semiconductor layer so as to cover the irregularities, and forming a diffraction grating fitted into the irregularities, forming an opening in the resistive layer in which the diffraction grating is formed, and regrowing the second conductive type semiconductor layer so as to fill the openings.

This makes it possible to laterally confine the guided light guided through the active layer based on the deposition of the resistive layer once, while arranging the diffraction grating close to the active layer. Furthermore, it is possible to improve the confinement of the current injected into the active layer while ensuring the refractive index difference between the second conductive type semiconductor layer and the diffraction grating. Therefore, it is possible to suppress the increase in crystal defects in the second conductive type semiconductor layer while suppressing the complication of the manufacturing process. Furthermore, it is possible to increase the coupling coefficient between the guided light and the diffraction grating, and it is possible to reduce the threshold current of the semiconductor light emitting element while suppressing heat generation from the semiconductor light emitting element. As a result, it is possible to stabilize the oscillation wavelength, and it is possible to increase the output while ensuring the reliability of the semiconductor light emitting element.

In addition, a method for manufacturing a semiconductor light-emitting device according to one aspect of the present invention includes the steps of sequentially stacking an active layer, a second conductive type semiconductor layer, and a resistive layer having a higher resistance than the second conductive type semiconductor layer on the first conductive type semiconductor layer, forming an opening in the resistive layer with a diffraction grating on both sides, and re-growing the second conductive type semiconductor layer so that the diffraction grating and the opening are embedded.

This makes it possible to form a waveguide layer in the opening that laterally confines the guided light that is guided through the active layer, and at the same time form a diffraction grating on both sides of the waveguide layer. In addition, it is possible to increase the refractive index difference between the second conductive type semiconductor layer and the diffraction grating while suppressing an increase in crystal defects in the second conductive type semiconductor layer. Therefore, it is possible to stably form an inner stripe type semiconductor laser having a DFB structure while suppressing an increase in the number of processes.

In one aspect of the present invention, the coupling coefficient between the guided light and the diffraction grating can be increased.

1 is a perspective view illustrating a configuration of a semiconductor light emitting device according to a first embodiment. 1A is a plan view showing the configuration of a resistive layer of a semiconductor light-emitting element according to a first embodiment; FIG. 1B is a cross-sectional view showing the configuration of the semiconductor light-emitting element according to the first embodiment cut along the horizontal direction of the waveguiding direction; and FIG. 1C is a diagram showing the refractive index of each layer of the semiconductor light-emitting element according to the first embodiment. 1A is a cross-sectional view showing the configuration of a semiconductor light-emitting device according to a comparative example cut along a horizontal direction of the waveguide direction, and FIG. 1B is a cross-sectional view showing the configuration of a semiconductor light-emitting device according to a comparative example cut along the waveguide direction. 4 is a diagram showing the relationship between the height of the diffraction grating and the coupling coefficient of the semiconductor light emitting device according to the first embodiment in comparison with a semiconductor light emitting device of a comparative example. FIG. 1A is a plan view showing the configuration of a resistive layer of a semiconductor light-emitting device according to a second embodiment; FIG. 1B is a cross-sectional view showing the configuration of the semiconductor light-emitting device according to the second embodiment cut along the horizontal direction of the waveguiding direction; and FIG. 1C is a diagram showing the refractive index of each layer of the semiconductor light-emitting device according to the second embodiment. 11A and 11B are plan views showing an example of a method for manufacturing a semiconductor light-emitting element according to a third embodiment, (a2) is a cross-sectional view cut along the waveguiding direction of (a1), and (b2) is a cross-sectional view cut along the waveguiding direction of (b1). 11A is a plan view showing an example of a manufacturing method of a semiconductor light-emitting element according to a third embodiment, FIG. 11A is a cross-sectional view taken along the waveguiding direction at the position of the diffraction grating in FIG. 11A, and FIG. 11B is a cross-sectional view taken along the waveguiding direction at the position of the waveguide in FIG. 11A is a plan view showing an example of a manufacturing method of a semiconductor light-emitting element according to a third embodiment, FIG. 11A is a cross-sectional view taken along the waveguiding direction at the position of the diffraction grating in FIG. 11A, and FIG. 11B is a cross-sectional view taken along the waveguiding direction at the position of the waveguide in FIG. FIG. 13 is a perspective view showing a configuration of a semiconductor light emitting device according to a fourth embodiment. 1A is a plan view showing a configuration of a semiconductor light emitting device according to a fourth embodiment, and FIG. 1B is a cross-sectional view taken along the line X1-X1 in FIG. 13A and 13B are plan views showing an example of a method for manufacturing a semiconductor light-emitting element according to a fifth embodiment, (a2) is a cross-sectional view cut along the waveguiding direction of (a1), and (b2) is a cross-sectional view cut along the waveguiding direction of (b1). 13A and 13B are plan views showing an example of a method for manufacturing a semiconductor light-emitting element according to a fifth embodiment, (a2) is a cross-sectional view cut along the waveguiding direction of (a1), and (b2) is a cross-sectional view cut along the waveguiding direction of (b1). 13A is a plan view showing an example of a manufacturing method of a semiconductor light-emitting element according to a fifth embodiment, FIG. 13A is a cross-sectional view taken along the waveguiding direction at the position of the diffraction grating in FIG. 13A, and FIG. 13B is a cross-sectional view taken along the waveguiding direction at the position of the waveguide in FIG. 13A is a plan view showing an example of a manufacturing method of a semiconductor light-emitting element according to a fifth embodiment, FIG. 13A is a cross-sectional view taken along the waveguiding direction at the position of the diffraction grating in FIG. 13A, and FIG. 13B is a cross-sectional view taken along the waveguiding direction at the position of the waveguide in FIG. 13A is a plan view showing the configuration of a resistive layer of a semiconductor light-emitting element according to a sixth embodiment, and FIG. 13B is a cross-sectional view showing the configuration of the semiconductor light-emitting element according to the sixth embodiment cut along the horizontal direction of the waveguiding direction. 13 is a plan view showing a configuration of a resistive layer of a semiconductor light emitting device according to a seventh embodiment. FIG. 13 is a cross-sectional view of the configuration of a semiconductor light emitting device according to a seventh embodiment, taken along the waveguiding direction at the position of a second-order diffraction grating. FIG. 16(a) and (b) are diagrams showing the refractive index distribution of the diffraction grating of FIG. 15, and (c) and (d) are diagrams showing the relationship between the phase and energy of a standing wave formed in the waveguide of FIG. 15. FIG. 16 is a relationship diagram between the refractive index and the position in the waveguiding direction, showing as examples the second-order diffraction grating and the third-order diffraction grating shown in FIG. 15, as parameters that can be adjusted when changing the relative positional relationship between a plurality of diffraction gratings. FIG. 13 is a diagram showing the relationship between the grating interval shift and the stop band width when the duty of the diffraction grating of the semiconductor light emitting device according to the seventh embodiment is changed. 13A to 13C are diagrams illustrating a method for maximizing the stop band width of the semiconductor light emitting device according to the seventh embodiment. 13 is a plan view showing a configuration of a resistive layer of a semiconductor light emitting device according to an eighth embodiment. FIG. 13A and 13B are diagrams showing the refractive index distribution of a diffraction grating of a semiconductor light-emitting element according to the ninth embodiment, and 13C and 13D are diagrams showing the relationship between the phase and energy of a standing wave formed in a waveguide of a semiconductor light-emitting element according to the ninth embodiment. FIG. 13 is a diagram showing the relationship between the grating shift and the stop band width when the duty of the diffraction grating of the semiconductor light emitting device according to the ninth embodiment is changed. 13 is a plan view showing the configuration of a resistive layer of the semiconductor light emitting device according to the tenth embodiment. FIG. FIG. 13 is a diagram showing the relationship between the height of a diffraction grating and a coupling coefficient. 11A is a plan view showing a method for manufacturing a semiconductor light-emitting element according to an eleventh embodiment, and FIG. 11B is a cross-sectional view taken along the waveguide direction of FIG. 11A is a plan view showing a method for manufacturing a semiconductor light-emitting element according to an eleventh embodiment, and FIG. 11B is a cross-sectional view taken along the waveguide direction of FIG. 11A is a plan view showing a method for manufacturing a semiconductor light-emitting element according to an eleventh embodiment, and FIG. 11B is a cross-sectional view taken along the waveguide direction of FIG. 11A is a plan view showing a method for manufacturing a semiconductor light-emitting element according to an eleventh embodiment, and FIG. 11B is a cross-sectional view taken along the waveguide direction of FIG. 11A is a plan view showing a method for manufacturing a semiconductor light-emitting element according to an eleventh embodiment, and FIG. 11B is a cross-sectional view taken along the waveguide direction of FIG. 12A is a plan view showing a method for manufacturing a semiconductor light-emitting element according to a twelfth embodiment, and FIG. 12B is a cross-sectional view taken along the waveguide direction of FIG. 12A is a plan view showing a method for manufacturing a semiconductor light-emitting element according to a twelfth embodiment, and FIG. 12B is a cross-sectional view taken along the waveguide direction of FIG. 12A is a plan view showing a method for manufacturing a semiconductor light-emitting element according to a twelfth embodiment, and FIG. 12B is a cross-sectional view taken along the waveguide direction of FIG. 12A is a plan view showing a method for manufacturing a semiconductor light-emitting element according to a twelfth embodiment, and FIG. 12B is a cross-sectional view taken along the waveguide direction of FIG.

Below, the embodiments of the present invention will be described in detail with reference to the attached drawings. Note that the following embodiments do not limit the present invention, and not all of the combinations of features described in the embodiments are necessarily essential to the configuration of the present invention. The configuration of the embodiments may be modified or changed as appropriate depending on the specifications of the device to which the present invention is applied and various conditions (conditions of use, environment of use, etc.). The technical scope of the present invention is determined by the claims, and is not limited by the individual embodiments below. Also, the drawings used in the following description may differ in scale and shape from the actual structure in order to make each configuration easier to understand.

In the following description, a nitride semiconductor laser capable of emitting blue laser light in the 444 nm wavelength band is used as an example, but it may be an AlGaInN semiconductor laser capable of emitting blue laser light in the 405 nm wavelength band, or an AlGaN semiconductor laser capable of emitting near-ultraviolet laser light with an emission wavelength of 390 nm or less.

Figure 1 is a perspective view showing the configuration of the semiconductor light-emitting device according to the first embodiment, Figure 2(a) is a plan view showing the configuration of the resistive layer of the semiconductor light-emitting device according to the first embodiment, Figure 2(b) is a cross-sectional view showing the configuration of the semiconductor light-emitting device according to the first embodiment cut along the lateral direction of the waveguiding direction, and Figure 2(c) is a diagram showing the refractive index of each layer of the semiconductor light-emitting device according to the first embodiment. Note that Figure 2(b) shows the configuration cut at the position of line X1-X1 in Figure 2(a). Also, for ease of understanding, the end face reflective film in Figure 2(a) and the electrode in Figure 2(b) have been omitted in Figure 1.

1, 2(a) and 2(b), the semiconductor laser LA includes an n-type nitride semiconductor layer E1, an active layer 15, a p-type nitride semiconductor layer E2, a resistive layer RA and a confinement layer E3. The active layer 15 is laminated on the n-type nitride semiconductor layer E1. The p-type nitride semiconductor layer E2 is laminated on the active layer 15. The nitride semiconductor can have a composition of, for example, In _x Al _y Ga _1-x-y N (0≦x≦1, 0≦y≦1, 0≦x+y≦1).

In order to suppress the diffusion of impurities from the n-type nitride semiconductor layer E1 to the active layer 15, an undoped nitride guide layer 14 may be provided between the n-type nitride semiconductor layer E1 and the active layer 15. In order to suppress the diffusion of impurities from the p-type nitride semiconductor layer E2 to the active layer 15, an undoped nitride guide layer 16 may be provided between the p-type nitride semiconductor layer E2 and the active layer 15.

The n-type nitride semiconductor layer E1 includes an n-type nitride cladding layer 12 and an n-type nitride guide layer 13. The n-type nitride cladding layer 12 and the n-type nitride guide layer 13 are sequentially stacked on the n-type nitride semiconductor substrate 11.

The p-type nitride semiconductor layer E2 includes a p-type carrier block layer 17 and p-type nitride guide layers 18 and 18A. The p-type carrier block layer 17 and the p-type nitride guide layers 18 and 18A are sequentially stacked on the undoped nitride guide layer 16. The p-type nitride guide layers 18 and 18A can be made of the same material. The p-type nitride semiconductor layer E2 includes a waveguide layer WA. The waveguide layer WA guides the guided light while confining the guided light in the lateral direction D2 of the guide direction D1 of the guided light guided through the active layer 15. The waveguide layer WA can be made of a p-type nitride guide layer 18A on the p-type nitride guide layer 18.

The resistive layer RA is located in a part of the p-type nitride semiconductor layer E2. The position of the resistive layer RA in the p-type nitride semiconductor layer E2 in the vertical direction D3 of the waveguiding direction D1 is not particularly limited. For example, the position of the top surface of the resistive layer RA may be equal to the position of the top surface of the p-type nitride guide layer 18, or may be lower than the position of the top surface of the p-type nitride guide layer 18. The position of the bottom surface of the resistive layer RA may be equal to the position of the bottom surface of the p-type nitride guide layer 18, or may be higher than the position of the bottom surface of the p-type nitride guide layer 18.

The resistive layer RA has a smaller refractive index and a larger resistance than the p-type nitride semiconductor layer E2. Here, the resistive layer RA can be arranged in a part of the p-type nitride semiconductor layer E2 so as to configure at least one of a refractive index guided type and a gain guided type Fabry-Perot resonator and have a DFB structure. The resistive layer RA can be, for example, a high resistance layer made of AlN.

The resistive layer RA has an opening KA and a diffraction grating EA. The pitch Λ1 of the diffraction grating EA can be made to match the oscillation period of the laser light guided through the waveguide layer WA. The diffraction grating EA is located on both sides of the waveguide layer WA. In this case, unevenness is formed on both sides of the waveguide layer WA, and the unevenness of the diffraction grating EA can be fitted into the unevenness on both sides of the waveguide layer WA. In this case, by embedding the p-type nitride guide layer 18A in the recesses of the diffraction grating EA and the opening KA, the difference in refractive index between the projections and recesses of the diffraction grating EA can be increased while forming the waveguide layer WA in the p-type nitride semiconductor layer E2.

The opening KA and the diffraction grating EA are recessed from the end faces MA, MB of the active layer 15. The diffraction grating EA can be recessed from the end faces MA, MB of the active layer 15 by a distance equal to or greater than the period of the diffraction grating EA. Here, by recessing the opening KA and the diffraction grating EA from the end faces MA, MB of the active layer 15, a non-current injection region NJ can be provided near the end faces MA, MB of the active layer 15. This makes it possible to suppress heat generation from the end faces MA, MB of the active layer 15 and protect the end faces MA, MB of the active layer 15.

If the coupling coefficient of the diffraction grating EA is κ and the resonator length of the semiconductor laser LA is L, it is preferable to satisfy the condition 1≦κ·L≦3. This makes it possible to stabilize the oscillation wavelength while lowering the threshold value and increasing the efficiency of the semiconductor laser LA.

The confinement layer E3 is provided on the p-type nitride semiconductor layer E2. In this case, the confinement layer E3 can be located on the diffraction grating EA and the waveguide layer WA. The confinement layer E3 has a lower refractive index than the p-type nitride semiconductor layer E2. In this case, the confinement layer E3 can confine the guided light that is guided through the active layer 15 in the vertical direction E3. The confinement layer E3 can include, for example, a p-type nitride cladding layer 20.

A p-type nitride contact layer 21 is laminated on the p-type nitride cladding layer 20. The p-type nitride contact layer 21 can make ohmic contact with an electrode 22 that injects current into the active layer 15.

An electrode 22 is formed on the p-type nitride contact layer 21 to inject current into the active layer 15 through the opening KA. The electrode 22 may have a layered structure of Ti/Pt/Au. The thicknesses of the Ti/Pt/Au layers may be set to, for example, 100/50/300 nm.

Examples of materials that can be used for each layer include the following: an n-type GaN substrate as the n-type nitride semiconductor substrate 11, an _n -type _{Al0.02Ga0.98N} layer as the n-type nitride cladding layer 12, an n-type GaN layer as the n-type nitride guide layer 13, and an _{In0.02Ga0.99N} layer as the undoped nitride guide layer 14. Also _, a single quantum well layer consisting of _{an In0.02Ga0.98N} barrier layer/ _{In0.15Ga0.88N well} layer/ _{In0.02Ga0.98N} barrier layer can _be used for the active layer 15. Furthermore, the undoped nitride guide layer 16 can be an _{In0.02Ga0.99N} layer, the _p -type carrier block layer 17 can be a _p -type _{Al0.22Ga0.78N} layer, the p-type nitride guide layers 18 and 18A can be a p-type GaN layer, and the p-type nitride cladding layer 20 and the p-type nitride contact layer 21 can be a p _- type _{Al0.02Ga0.98N} layer and a p-type GaN layer, respectively.

The thickness of the n-type nitride cladding layer 12 can be set to, for example, 700 nm, and the donor concentration N _D can be set to, for example, 1×10 ¹⁷ cm ⁻³ . The thickness of the n-type nitride guide layer 13 can be set to, for example, 50 nm, and the donor concentration N _D can be set to, for example, 1×10 ¹⁷ cm ⁻³ . The thickness of the undoped nitride guide layer 14 can be set to, for example, 136 nm. The thicknesses of the barrier layer/well layer/barrier layer of the quantum well layer of the active layer 15 can be set to, for example, 10/9/10 nm. The thickness of the undoped nitride guide layer 16 can be set to, for example, 135 nm. The thickness of the p-type carrier block layer 17 can be set to, for example, 4 nm, and the acceptor concentration N _A can be set to, for example, 1×10 ¹⁸ cm ⁻³ . The total thickness of the p-type nitride guide layers 18, 18A can be set to, for example, 150 nm and the acceptor concentration N _A to 1×10 ¹⁸ cm ^-3 . The thickness of the p-type nitride cladding layer 20 can be set to, for example, 700 nm and the acceptor concentration N _A to 1×10 ¹⁸ cm ^-3 . The thickness of the p-type nitride contact layer 21 can be set to, for example, 60 nm and the acceptor concentration N _A to 1×10 ¹⁸ cm ^-3 .

2C, the refractive index of the n-type nitride cladding layer 12 is smaller than the refractive index of the n-type nitride guide layer 13. In addition, the refractive index of the n-type nitride guide layer 13 is smaller than the refractive index of the undoped nitride guide layer 14, which can be smaller than the refractive index of the active layer 15.
The refractive index of the p-type nitride contact layer 21 is greater than that of the p-type nitride cladding layer 20. The refractive index of the p-type nitride cladding layer 20 is smaller than that of the p-type nitride guide layer 18, which is smaller than that of the undoped nitride guide layer 16. The refractive index of the undoped nitride guide layer 16 can be smaller than that of the active layer 15. The refractive index of the p-type carrier block layer 17 can be smaller than that of the p-type nitride guide layer 18.

As shown in FIG. 2(a), end face reflective films 24, 25 are formed on the end faces MA, MB of the semiconductor laser LA. At this time, it is preferable to set the reflectance of the end face MA to 2% or less, and the reflectance of the end face MB to 90% or more. This makes it possible to reduce the variation in the characteristics of the semiconductor laser LA while suppressing the decrease in the light emission efficiency of the semiconductor laser LA.

In this case, the end face reflection film 24 may have a laminated structure of AlN/ _SiO2 . Here, the thickness of AlN/ _SiO2 may be set to, for example, 30/300 nm. The end face reflection film 25 may have a laminated structure of AlN/( _SiO2 / _Ta2O5 ) ⁶ / _SiO2 . Here, the thickness of AlN/ _{( SiO2} / _Ta2O5 ) ⁶ / _{SiO2 may} be set to, for example, 30/(60/40) ^6/10 nm.

In addition, by providing an opening KA and a diffraction grating EA in the resistive layer RA below the p-type nitride cladding layer 20, it is possible to provide the diffraction grating EA on both sides of the waveguide layer WA. This makes it possible to confine the guided light guided through the active layer 15 in the horizontal direction D2 and the vertical direction D3. It also makes it possible to position the diffraction grating EA close to the active layer 15, and to increase the refractive index difference between the p-type nitride guide layer 18A and the diffraction grating EA while suppressing an increase in crystal defects in the p-type nitride guide layer 18A. This makes it possible to improve the light emission efficiency of the semiconductor laser LA and increase the output of the semiconductor laser LA. Furthermore, it is possible to increase the coupling coefficient between the guided light and the diffraction grating EA while suppressing a decrease in the reliability of the semiconductor laser LA, and to stabilize the oscillation wavelength.

In addition, by constructing the waveguide layer WA from GaN and the resistive layer RA from AlN, it is possible to suppress the decrease in the thermal conductivity of the resistive layer RA while suppressing the deviation between the lattice constant of the resistive layer RA and the lattice constant of the waveguide layer WA. In addition, it is possible to ensure the refractive index difference between the p-type nitride guide layer 18A and the diffraction grating EA while constricting the current injected into the active layer 15. Therefore, it is possible to realize a blue-violet laser diode with a stable oscillation wavelength while suppressing the decrease in the heat dissipation from the active layer 15. Furthermore, it is possible to increase the coupling coefficient between the guided light and the diffraction grating EA while suppressing the increase in crystal defects in the p-type nitride guide layer 18A. As a result, it is possible to increase the light emission efficiency while suppressing the heat generation of the semiconductor laser LA, and it is possible to increase the output of the semiconductor laser LA, and it is possible to stabilize the oscillation wavelength while suppressing the decrease in the reliability of the semiconductor laser LA.

For example, if the waveguide layer WA is made of GaN and the resistive layer RA is made of AlN, then at a laser oscillation wavelength of 444 nm, the refractive index of the waveguide layer WA is 2.49 and the refractive index of the resistive layer RA is 2.18. By using such materials, the stop band width of the diffraction grating EA can be expanded and the SMSR can be increased. Specifically, an SMSR of about 30 to 40 dB can be ensured. In contrast, if the diffraction grating is made of an AlInGaN-based semiconductor with a high concentration of Al or In, the stop band width of the diffraction grating is about 0.23 nm and an SMSR of only about 10 dB can be obtained.

FIG. 3(a) is a cross-sectional view showing the configuration of a semiconductor light-emitting device according to a comparative example cut along the horizontal direction of the waveguide direction, and FIG. 3(b) is a cross-sectional view showing the configuration of a semiconductor light-emitting device according to a comparative example cut along the waveguide direction.
3(a) and 3(b), the semiconductor laser LA' has a ridge RA and a diffraction grating EA' instead of the resistive layer RA, the opening KA, and the diffraction grating EA of the semiconductor laser LA in Fig. 2(b). The other configurations of the semiconductor laser LA' can be configured in the same way as the semiconductor laser LA.

In this comparative example, the diffraction grating EA' is located below the active layer 15. In this case, the diffraction grating EA' can be formed in the n-type nitride cladding layer 12A on the n-type nitride cladding layer 12. The n-type nitride cladding layers 12 and 12A can be integrally formed from the same material. The diffraction grating EA' can be covered with the n-type nitride guide layer 13.

When forming the diffraction grating EA', for example, a pattern _of projections and recesses with a period (pitch: Λ) of 89.2 nm and a duty of 0.5 is formed on the surface of an n-type _{Al0.02Ga0.98N} layer formed on a GaN substrate by photolithography and etching, and an n-type GaN layer is then regrown thereon. The duty is the ratio of the width of the projections to the width within one period of the diffraction grating.

A p-type nitride cladding layer 20A is formed on the p-type nitride cladding layer 20. The p-type nitride cladding layers 20 and 20A can be made of the same material. The p-type nitride cladding layer 20A has a ridge RA. The ridge RA is provided across the end faces of the semiconductor laser LA' along the guiding direction D1 of the guided light that guides the active layer 15. At this time, the ridge RA can confine the guided light that guides the active layer 15 in the lateral direction D2 and the vertical direction D3 of the guiding direction D1. In this configuration, the p-type nitride contact layer 21 is formed on the top surface of the ridge RA.

Figure 4 shows the relationship between the height of the diffraction grating and the coupling coefficient of the semiconductor light-emitting device according to the first embodiment, in comparison with a semiconductor light-emitting device of a comparative example. Note that H1 shows the relationship between the height of the diffraction grating and the coupling coefficient in the configuration of Figure 2(b), and H2 shows the relationship between the height of the diffraction grating and the coupling coefficient in the configuration of Figure 3.

In Figure 4, the coupling coefficients of the comparative example in Figure 3 and the configuration in Figure 2(b) were compared in the case of a rectangular diffraction grating using a method similar to that described in the literature (IEEE J. Quantum Electron. QE-11, p. 867, 1975). According to this literature, for example, in the case of the TE mode, the coupling coefficient κ is given by the following formula:

where β is the propagation constant.
In the configuration of Fig. 2(b) and the comparative example of Fig. 3, when the heights of the diffraction gratings EA and EA' are equal, the configuration of Fig. 2(b) has a higher coupling coefficient than the comparative example of Fig. 3. As a result, in the configuration of Fig. 2(b), the stop band width can be made larger, making it easier to obtain a larger side mode suppression ratio (SMSR). Also, in the configuration of Fig. 2(b), when the height of the diffraction grating EA is 100 nm, κ·L is 1.4.

The refractive indices used in the estimation by the method described in the above-mentioned document were _n1 = 2.48, _n2 = 2.49, and n3 = 2.48 in the comparative example of Fig. 3, and _n1 = 2.18, _n2 = 2.49, and _n3 = _2.48 in the configuration of Fig. 2(b). In addition, the variables common to the configuration of Fig. 2(b) and the comparative example of Fig. 3 were t = 3 µm, _λ0 = 444 nm, and duty = 0.4.

This semiconductor laser LA can be used as a light source that generates 222 nm SHG (second harmonic generation) waves. 222 nm ultraviolet light is safer for humans than 254 nm ultraviolet light, which is used for sterilization purposes, and can prevent the onset of skin cancer and keratitis.

Figure 5(a) is a plan view showing the configuration of the resistive layer of the semiconductor light-emitting device according to the second embodiment, Figure 5(b) is a cross-sectional view showing the configuration of the semiconductor light-emitting device according to the second embodiment cut along the lateral direction of the waveguiding direction, and Figure 5(c) is a diagram showing the refractive index of each layer of the semiconductor light-emitting device according to the second embodiment. Note that Figure 5(b) shows the configuration cut at the position of line X1-X1 in Figure 5(a).

In Figures 5(a) and 5(b), the semiconductor laser LB has a transparent conductive layer 23 instead of the p-type nitride cladding layer 20 and the p-type nitride contact layer 21 of the semiconductor laser LA of Figure 2(b). The other points of the semiconductor laser LB can be configured in the same way as the semiconductor laser LA of Figure 2(b).

The transparent conductive layer 23 is a conductive layer transparent to the light generated in the active layer 15. The transparent conductive layer 23 is used as at least one of the guide layer or the cladding layer on the active layer 15. The transparent conductive layer 23 may contain at least one element selected from In, Sn, Zn, Ti, Nb, and Zr, and may be an oxide of these elements. For example, the transparent conductive layer 23 may be an ITO film, a ZnO film, a SnO film, or a TiO film. Here, as shown in FIG. 5(c), the refractive index of the transparent conductive layer 23 can be smaller than the refractive index of the p-type nitride guide layer 18. The transparent conductive layer 23 is preferably thinned within a range in which light can be confined to the perpendicular transverse mode. The perpendicular transverse mode is a propagation mode in the longitudinal direction D3 of the waveguiding direction D1. At this time, the thickness of the transparent conductive layer 23 is preferably 80 nm or more and 120 nm or less. An electrode 21 is formed on the transparent conductive layer 23. The transparent conductive layer 23 can make direct ohmic contact with the electrode 21.

Here, by making the refractive index of the transparent conductive layer 23 smaller than that of the p-type nitride guide layer 18, it is possible to confine the vertical lateral mode in the transparent conductive layer 23 while suppressing the thickening of the p-type nitride semiconductor layer E2. In addition, by stacking the transparent conductive layer 23 on the p-type nitride semiconductor layer E2, it is not necessary to provide a p-type nitride semiconductor contact layer on the transparent conductive layer 23 for contacting the electrode 22, and the resistance of the current injected into the active layer 15 via the transparent conductive layer 23 can be reduced. This makes it possible to reduce heat generation in the semiconductor laser LB, reduce optical loss during optical propagation, and improve slope efficiency.

Figures 6(a1), 6(b1), 7(a1) and 8(a1) are plan views showing an example of a method for manufacturing a semiconductor light-emitting device according to the third embodiment. Also, Figures 6(a2) and 6(b2) are cross-sectional views cut along the waveguiding direction of Figures 6(a1) and 6(b1), respectively. Also, Figures 7(a2) and 8(a2) are cross-sectional views cut along the waveguiding direction at the position of the diffraction grating of Figures 7(a1) and 8(a1), respectively. Also, Figures 7(a3) and 8(a3) are cross-sectional views cut along the waveguiding direction at the position of the waveguide of Figures 7(a1) and 8(a1), respectively. Note that Figures 6(a2), 6(b2), 7(a2), and 8(a2) show configurations cut along lines A1-A1 in Figures 6(a1), 6(b1), 7(a1), and 8(a1), respectively, and Figures 7(a3) and 8(a3) show configurations cut along lines B1-B1 in Figures 7(a1) and 8(a1), respectively.

This third embodiment can be applied to the manufacture of the semiconductor laser LA in FIG. 2(b). Note that in FIG. 6(a2), FIG. 6(b2), FIG. 7(a2), FIG. 7(a3), FIG. 8(a2), and FIG. 8(a3), the n-type nitride semiconductor substrate 11, the n-type nitride cladding layer 12, the n-type nitride guide layer 13, and the undoped nitride guide layer 14 in FIG. 2(b) are omitted.

6(a1) and 6(a2), an n-type nitride cladding layer 12, an n-type nitride guide layer 13, an undoped nitride guide layer 14, an active layer 15, an undoped nitride guide layer 16, a p-type carrier block layer 17, and a p-type nitride guide layer 18 are sequentially stacked on an n-type nitride semiconductor substrate 11 by epitaxial growth. Furthermore, a resistive layer RA is stacked on the p-type nitride guide layer 18 by a method such as epitaxial growth or sputtering. The epitaxial growth may be MOCVD (Metal Organic Chemical Vapor Deposition), MBE (Molecular Beam Epitaxy), or HVPE (Hydride Vapor Phase Epitaxy).

Next, as shown in FIG. 6(b1) and FIG. 6(b2), the resistive layer RA is patterned based on photolithography and dry etching techniques to form an opening KA in the resistive layer RA with a diffraction grating EA on both sides along the waveguiding direction D1. At this time, the concave and convex portions of the diffraction grating EA can be arranged on both sides of the opening KA along the waveguiding direction D1 with a period of the oscillation wavelength.

Next, as shown in Figures 7(a1), 7(a2) and 7(a3), a p-type nitride guide layer 18A is selectively formed on the p-type nitride guide layer 18 by epitaxial growth so as to be embedded in the opening KA. At this time, the p-type nitride guide layer 18A can be embedded in the recesses of the diffraction grating EA, and the refractive index difference between the recesses and protrusions of the diffraction grating EA can be determined by the refractive index of the resistive layer RA. In addition, a waveguide layer WA is formed in the opening KA with the diffraction grating EA provided on both sides along the waveguiding direction D1.

Next, as shown in Figures 8(a1), 8(a2), and 8(a3), a p-type nitride cladding layer 20 and a p-type nitride contact layer 21 are sequentially formed on the p-type nitride guide layer 18A and the resistive layer RA by epitaxial growth.

This makes it possible to form the waveguide layer WA in FIG. 2(a) in the opening KA and simultaneously form the diffraction grating EA on both sides of the waveguide layer WA, and to increase the refractive index difference between the p-type nitride guide layer 18A and the diffraction grating EA. This makes it possible to stably form an inner stripe type semiconductor laser having a DFB structure while suppressing an increase in the number of steps.

FIG. 9A is a perspective view showing the configuration of a semiconductor light emitting device according to the fourth embodiment.
9A and 9B, the semiconductor laser LC has a p-type nitride semiconductor layer E2' instead of the p-type nitride semiconductor layer E2 of the semiconductor laser LA of Fig. 2(b). Other points of the semiconductor laser LC can be configured in the same way as the semiconductor laser LA of Fig. 2(b).

9A and 9B, the p-type nitride semiconductor layer E2' includes a p-type carrier block layer 17 and p-type nitride guide layers 18, 18A, and 18A'. The p-type carrier block layer 17 and the p-type nitride guide layers 18, 18A, and 18A' are sequentially stacked on the undoped nitride guide layer 16. The p-type nitride guide layers 18, 18A, and 18A' can be made of the same material. The p-type nitride semiconductor layer E2' includes waveguide layers WA and WA'. The waveguide layers WA and WA' guide the guided light while confining the guided light in the lateral direction D2 of the guide direction D1 of the guided light guided through the active layer 15. The waveguide layer WA' can be made of a p-type nitride guide layer 18A' on the p-type nitride guide layer 18A.

The resistive layers RA and RA' are located in a portion of the p-type nitride semiconductor layer E2'. The resistive layers RA and RA' can be made of the same material. The resistive layers RA and RA' may be integrated with each other. The positions of the resistive layers RA and RA' in the p-type nitride semiconductor layer E2' in the vertical direction D3 of the waveguide direction D1 are not particularly limited.

The resistive layers RA and RA' have a smaller refractive index and a larger resistance than the p-type nitride semiconductor layer E2'. The resistive layer RA' is laminated on the resistive layer RA. Here, the resistive layers RA and RA' can form at least one of a refractive index guided type and a gain guided type Fabry-Perot resonator, and can be disposed in a part of the p-type nitride semiconductor layer E2' so as to have a DFB structure. The resistive layers RA and RA' can be, for example, high resistance layers made of AlN.

In addition, by constructing the waveguide layers WA and WA' from GaN and the resistive layers RA and RA' from AlN, it is possible to suppress the deviation between the lattice constant of the resistive layers RA and RA' and the lattice constant of the waveguide layers WA and WA' while suppressing the decrease in the thermal conductivity of the resistive layers RA and RA'. Furthermore, even if a diffraction grating EA is present, it is possible to ensure the refractive index difference between the p-type nitride guide layer 18A and the diffraction grating EA while improving the confinement of the current injected into the active layer 15. Therefore, it is possible to realize a blue-violet laser diode while suppressing the heat generation of the semiconductor laser LC. In addition, it is possible to increase the coupling coefficient between the guided light and the diffraction grating EA while suppressing the increase in crystal defects of the p-type nitride guide layer 18A and the decrease in the heat dissipation from the active layer 15. As a result, it is possible to increase the light emission efficiency while suppressing the temperature rise of the semiconductor laser LC, and to increase the output of the semiconductor laser LC. As a result, it is possible to stabilize the oscillation wavelength while suppressing the decrease in the reliability of the semiconductor laser LC.

In the semiconductor laser LC of Figures 9A and 9B, an example is shown in which a waveguide layer WA' without a diffraction grating on both sides is laminated on a waveguide layer WA with a diffraction grating EA on both sides, as in the case of the semiconductor laser LB shown in Figure 5, but a waveguide layer WA with a diffraction grating EA on both sides may also be laminated on a waveguide layer WA' without a diffraction grating on both sides.

Figures 10(a1), 10(b1), 11(a1), 11(b1), 12(a1) and 13(a1) are plan views showing an example of a method for manufacturing a semiconductor light-emitting device according to the fifth embodiment. Also, Figures 10(a2), 10(b2), 11(a2) and 11(b2) are cross-sectional views cut along the waveguiding direction of Figures 6(a1) and 6(b1), respectively. Also, Figures 12(a2) and 13(a2) are cross-sectional views cut along the waveguiding direction at the positions of the diffraction gratings of Figures 12(a1) and 13(a1), respectively. Furthermore, Figures 12(a3) and 13(a3) are cross-sectional views cut along the waveguiding direction at the positions of the waveguides of Figures 12(a1) and 13(a1), respectively. 10(a2), 10(b2), 11(a2), 12(a2), and 13(a2) show configurations cut along the lines A1-A1 in 10(a1), 10(b1), 11(a1), 12(a1), and 13(a1), respectively. Also, 11(b2), 12(a3), and 13(a3) show configurations cut along the lines B1-B1 in 11(b1), 12(a1), and 13(a1), respectively.

This fifth embodiment can be applied to the manufacture of the semiconductor laser LC of FIG. 9. Note that in FIG. 10(a2), FIG. 10(b2), FIG. 11(a2), FIG. 11(b2), FIG. 12(a2), FIG. 12(a3), FIG. 13(a2), and FIG. 13(a3), the n-type nitride semiconductor substrate 11, the n-type nitride cladding layer 12, the n-type nitride guide layer 13, and the undoped nitride guide layer 14 of FIG. 9 are omitted.

In Figures 10(a1) and 10(a2), an n-type nitride cladding layer 12, an n-type nitride guide layer 13, an undoped nitride guide layer 14, an active layer 15, an undoped nitride guide layer 16, a p-type carrier block layer 17, and p-type nitride guide layers 18 and 18A are sequentially stacked on an n-type nitride semiconductor substrate 11 by epitaxial growth.

Next, as shown in Figures 10(b1) and 10(b2), the p-type nitride guide layer 18A is patterned using photolithography and dry etching techniques to form alternating convex portions QT and concave portions QB in the p-type nitride guide layer 18A at a period of the oscillation wavelength along the waveguide direction D1.

Next, as shown in FIG. 11(a1) and FIG. 11(a2), resistive layers RA, RA' are formed sequentially on the p-type nitride guide layers 18, 18A by epitaxial growth or sputtering. The resistive layers RA, RA' can be formed collectively in a single film formation process. At this time, the resistive layer RA can be formed so as to fill the recessed portion QB of the p-type nitride guide layer 18A, and the resistive layer RA' can be formed so as to cover the protruding portion QT of the p-type nitride guide layer 18A and the resistive layer RA.

Next, as shown in FIG. 11(b1) and FIG. 11(b2), the resistive layers RA, RA' are patterned using photolithography and dry etching techniques to form openings KA, KA' in the resistive layers RA, RA', respectively, along the waveguide direction D1. At this time, the resistive layers RA, RA' are removed in the openings KA, KA', respectively, and the protrusions QT and recesses QB of the p-type nitride guide layer 18' are exposed from the resistive layers RA, RA'.

Next, as shown in Figures 12(a1), 12(a2) and 12(a3), a p-type nitride guide layer 18A' is selectively formed by epitaxial growth on the p-type nitride guide layers 18, 18A so as to be embedded in the openings KA, KA'. At this time, a waveguide layer WA is formed in the opening KA with a diffraction grating EA on both sides along the waveguiding direction D1 as shown in Figure 5. Also, a waveguide layer WA' without a diffraction grating on both sides is formed in the opening KA'.

Next, as shown in Figures 13(a1), 13(a2) and 13(a3), a p-type nitride cladding layer 20 and a p-type nitride contact layer 21 are sequentially formed on the p-type nitride guide layer 18A' and the resistive layer RA' by epitaxial growth.

This makes it possible to laterally confine the guided light guided through the active layer 15 based on the deposition of the resistive layers RA and RA' once, while arranging the diffraction grating KA close to the active layer 15. In addition, it is possible to constrict the current injected into the active layer 15 at the position of the opening KA' while ensuring the refractive index difference between the p-type nitride guide layer 18A and the diffraction grating KA. Therefore, it is possible to increase the coupling coefficient between the guided light and the diffraction grating KA while suppressing the increase in crystal defects in the p-type nitride guide layers 18A and 18A' while suppressing the complication of the manufacturing process. In addition, it is possible to reduce the threshold current of the semiconductor laser LC while suppressing heat generation of the semiconductor laser LC. As a result, it is possible to stabilize the oscillation wavelength while suppressing an increase in the cost, and to increase the output while ensuring the reliability of the semiconductor laser LC.

Figure 14(a) is a plan view showing the configuration of the resistive layer of the semiconductor light-emitting device according to the sixth embodiment, and Figure 14(b) is a cross-sectional view showing the configuration of the semiconductor light-emitting device according to the sixth embodiment cut along the lateral direction of the waveguiding direction. Note that Figure 14(b) shows the configuration cut at the position of line X1-X1 in Figure 14(a).

In Fig. 14(a) and Fig. 14(b), the semiconductor laser LD has a resistive layer RD instead of the resistive layer RA of the semiconductor laser LA of Fig. 2(b). The other points of the semiconductor laser LD can be configured in the same way as the semiconductor laser LA of Fig. 2(b).

The resistive layer RD can be configured in the same way as the resistive layer RA, except that the position in the vertical direction D3 in the p-type nitride guide layer 18 is different from the position in the vertical direction D3 of the resistive layer RA. That is, the top surface of the resistive layer RD can be located at a position lower than the top surface of the p-type nitride guide layer 18. This allows the diffraction grating EA to be closer to the active layer 15, and the coupling coefficient between the guided light and the diffraction grating EA can be improved.

Figure 15 is a plan view showing the configuration of the resistive layer of the semiconductor light-emitting device according to the seventh embodiment, and is a schematic diagram showing the state of standing waves formed within the semiconductor light-emitting device for the purpose of explanation. Also, Figure 16 is a cross-sectional view of the configuration of the semiconductor light-emitting device according to the seventh embodiment cut along the waveguiding direction at the position of the second-order diffraction grating. Note that Figure 16 shows the configuration cut at the position of line A1-A1 in Figure 15.

In FIG. 15, the semiconductor laser LE has a p-type nitride semiconductor layer E2'' instead of the p-type nitride semiconductor layer E2 of the semiconductor laser LB in FIG. 5(b). The p-type nitride semiconductor layer E2'' has a resistive layer RE instead of the resistive layer RA. In other respects, the semiconductor laser LE can be configured in the same way as the semiconductor laser LB in FIG. 5(b).

The resistive layer RE is located in a part of the p-type nitride semiconductor layer E2''. The position of the resistive layer RE in the p-type nitride semiconductor layer E2'' in the vertical direction D3 of the waveguide direction D1 is not particularly limited. The resistive layer RE has a smaller refractive index and a larger resistance than the p-type nitride semiconductor layer E2''. Here, the resistive layer RE can configure at least one of a refractive index guided type and a gain guided type Fabry-Perot resonator. In addition, it can be disposed in a part of the p-type nitride semiconductor layer E2'' so as to have a high-order DFB structure. The resistive layer RE has multiple high-order diffraction gratings with a greatest common denominator of 1 and different orders. The resistive layer RE can be, for example, a high-resistance layer made of AlN.

As shown in FIG. 15, the resistive layer RE has an opening KE, a second-order diffraction grating EE2, and a third-order diffraction grating EE3. A waveguide layer WE is provided in the opening KE. The pitch Λ2 of the second-order diffraction grating EE2 can be matched to a length that is twice the oscillation period of the laser light guided through the waveguide layer WE. The pitch Λ3 of the third-order diffraction grating EE3 can be matched to a length that is three times the oscillation period of the laser light guided through the waveguide layer WE. The second-order diffraction grating EE2 and the third-order diffraction grating EE3 are located on both sides of the waveguide layer WE. At this time, unevenness with a pitch Λ2 is formed on one side of the waveguide layer WE, and the unevenness of the second-order diffraction grating EE2 can be fitted into the unevenness on one side of the waveguide layer WE. The other side of the waveguide layer WE has a concave-convex shape with a pitch Λ3, and the concave-convex shape of the third-order diffraction grating EE3 can be fitted into the concave-convex shape of the other side of the waveguide layer WE. At this time, by embedding the p-type nitride guide layer 18A into the concave portion of the second-order diffraction grating EE2 (the gray portion of the diffraction grating formation portion in the figure), the concave portion of the third-order diffraction grating EE3 (the gray portion of the diffraction grating formation portion in the figure), and the opening KE (the portion encircling the diffraction grating and the waveguide layer WE in the figure), the difference in refractive index between the convex portion and the concave portion of each of the second-order diffraction grating EE2 and the third-order diffraction grating EE3 can be increased, and the waveguide layer WE can be formed in the p-type nitride semiconductor layer E2'' (see FIG. 16).

Here, the second-order diffraction grating EE2 and the third-order diffraction grating EE3 have regions in which at least one of the following portions coincide with each other.
1) the center of the convex portion ST2 of the second-order diffraction grating EE2 and the center of the convex portion ST3 of the third-order diffraction grating EE3, 2) the center of the concave portion SB2 of the second-order diffraction grating EE2 and the center of the concave portion SB3 of the third-order diffraction grating EE3, 3) the center of the convex portion ST2 of the second-order diffraction grating EE2 and the center of the concave portion SB3 of the third-order diffraction grating EE3, 4) the center of the concave portion SB2 of the second-order diffraction grating EE2 and the center of the convex portion ST3 of the third-order diffraction grating EE3

For example, at positions PC1, PC3, and PC5 in the waveguiding direction D1, the center of the convex portion ST2 of the second-order diffraction grating EE2 coincides with the center of the convex portion ST3 of the third-order diffraction grating EE3. At positions PC2, PC4, and PC6 in the waveguiding direction D1, the center of the concave portion SB2 of the second-order diffraction grating EE2 coincides with the center of the convex portion ST3 of the third-order diffraction grating EE3.

The opening KE, second-order diffraction grating EE2, and third-order diffraction grating EE3 are formed at positions recessed from the end faces MA, MB of the active layer 15. The second-order diffraction grating EE2 and third-order diffraction grating EE3 can be recessed from the end faces MA, MB of the active layer 15 by a distance equal to or greater than the period of each of the second-order diffraction grating EE2 and third-order diffraction grating EE3.

Here, by setting the greatest common divisor of the orders of the second-order diffraction grating EE2 and the third-order diffraction grating EE3 to 1, the period of the second-order diffraction grating EE2 and the third-order diffraction grating EE3 can be increased while matching the diffraction conditions with the guide direction D1 of the guided light guided through the active layer 15. This makes it possible to stabilize the oscillation wavelength while suppressing a decrease in oscillation efficiency. Furthermore, it is possible to realize a blue-violet laser diode with a highly stable oscillation wavelength while mitigating the manufacturing difficulties associated with miniaturizing the second-order diffraction grating EE2 and the third-order diffraction grating EE3.

That is, the second-order diffraction grating EE2 diffracts the emitted light not only in the in-plane direction (180° direction: D1 direction in the cross-sectional view of FIG. 16 and the direction perpendicular to the paper surface), but also in the 90° direction (D3 direction in FIG. 16). The third-order diffraction grating EE3 diffracts the emitted light not only in the in-plane direction (180°), but also in directions of about 70° and about 110° with respect to the D1 axis in FIG. 16. However, since the greatest common denominator of the orders of the second-order diffraction grating EE2 and the third-order diffraction grating EE3 is 1, only diffraction in the in-plane direction (180°) occurs, and the pitch is increased compared to the first-order diffraction grating, while providing the same effect as the first-order diffraction grating.

In addition, by providing an area in which at least one of the centers of the convex portions, the centers of the concave portions, and the centers of the convex portions and the concave portions of the second-order diffraction grating EE2 and the third-order diffraction grating EE3 coincide, the difference in energy density of the electric field of the standing wave VE formed by the second-order diffraction grating EE2 and the third-order diffraction grating EE3 can be increased, and the stop band width can be increased. Therefore, the SMSR of the multiple high-order diffraction gratings formed by the second-order diffraction grating EE2 and the third-order diffraction grating EE3 can be increased, and the coupling coefficient between the guided light and the high-order diffraction grating can be increased.

Figures 17(a) and 17(b) show the refractive index distribution of the diffraction grating shown in Figure 15. The horizontal axis of the figure is the position in the light guide direction, and the vertical axis is the magnitude of the refractive index. Figures 17(c) and 17(d) show the relationship between the phase and energy of the standing wave formed in the waveguide of Figure 15. The horizontal axis of the figure is the position in the light guide direction, and the vertical axis is the magnitude of the amplitude. Note that Figure 17(a) shows the refractive index distribution in the waveguiding direction D1 when the period (pitch: Λ2) is 178.3 nm and the duty is 0.2 in the second-order diffraction grating EE2 of Figure 15, and Figure 17(b) shows the refractive index distribution in the waveguiding direction D1 when the period (pitch: Λ3) is 267.5 nm and the duty is 0.2 in the third-order diffraction grating EE3 of Figure 15.

In Fig. 17(a) and Fig. 17(b), the second-order diffraction grating EE2 and the third-order diffraction grating EE3 have points PC12 and PC14 where the centers of the convex parts and the centers of the convex parts coincide with each other, and points PC11 and PC13 where the centers of the concave parts and the centers of the convex parts coincide with each other. At this time, even if the wavelength is the same, the energy density u = 1/2 ^εE2 of the electric field E, which is indicated by the magnitude of the amplitude, differs depending on the position of the waveguiding direction D1 of the standing waves VE1 and VE2 relative to the diffraction grating. ε is the refractive index of the medium in which the electric field E is formed. The difference in the energy density u of the standing waves VE1 and VE2 corresponds to the stop band width. At this time, the difference in the amplitude between the standing waves VE1 and VE2 increases at points PC12 and PC14 where the centers of the convex parts of the second-order diffraction grating EE2 and the third-order diffraction grating EE3 coincide with each other, and at points PC11 and PC13 where the centers of the concave parts of the second-order diffraction grating EE2 and the third-order diffraction grating EE3 coincide with each other. In other words, by providing points PC12 and PC14 where the centers of the convex portions of the second-order diffraction grating EE2 and the third-order diffraction grating EE3 coincide with each other and points PC11 and PC13 where the centers of the concave portions of the second-order diffraction grating EE2 and the third-order diffraction grating EE3 coincide with each other, the stop band width can be increased, and the coupling coefficient between the guided light and the high-order diffraction grating can be increased.

FIG. 18 is a relationship diagram between the refractive index and the position in the waveguiding direction, showing as examples the second-order diffraction grating and the third-order diffraction grating shown in FIG. 15, as parameters that can be adjusted when changing the relative positional relationship between a plurality of diffraction gratings.
In Fig. 18, there are countless ways to select the relative positional relationship of the concaves and convexes of the second-order diffraction grating EE2 and the third-order diffraction grating EE3. When changing the relative positional relationship of the concaves and convexes of the second-order diffraction grating EE2 and the third-order diffraction grating EE3, the grating shift FK between the second-order diffraction grating EE2 and the third-order diffraction grating EE3 may be changed, the duty DY2 of the second-order diffraction grating EE2 may be changed, the duty DY3 of the third-order diffraction grating EE3 may be changed, or these changes may be combined. The grating shift FK is the difference in physical distance from the end face of the resonator between the second-order diffraction grating and the third-order diffraction grating, and this grating shift creates a phase shift of the wave formed in the resonator.

FIG. 19A is a diagram showing the relationship between the grating shift and the stop band width when the duty of the diffraction grating of the semiconductor light emitting device according to the seventh embodiment is changed.
19A, the stop band width was estimated when the duty DY2 of the second-order diffraction grating EE2 and the duty DY3 of the third-order diffraction grating EE3 were set to the same value and the inter-grating shift FK was changed between 0.1 and 0.5. Here, for the duty DY2 of the second-order diffraction grating and the duty DY3 of the third-order diffraction grating, the ◆ mark indicates the case of 0.1, the ■ mark indicates the case of 0.2, the ▲ mark indicates the case of 0.3, the × mark indicates the case of 0.4, and the asterisk indicates the case of 0.5.

From these results, it was found that the stop band width changes depending on the relative positions of multiple diffraction gratings. In this estimation, the largest stop band value was obtained when the duty DY2 of the second-order diffraction grating EE2 and the duty DY3 of the third-order diffraction grating EE3 were 0.2 and the inter-grating shift FK was 0.5.

FIG. 19B is a diagram showing a method for maximizing the stop band width of the semiconductor light emitting device according to the seventh embodiment.
In FIG. 19B , when the duty DY2 of the second-order diffraction grating EE2 and the duty DY3 of the third-order diffraction grating EE3 are changed, when the duty DY2 of the second-order diffraction grating EE2 is 0.3, the duty DY3 of the third-order diffraction grating EE3 is 0.5, and the inter-grating shift FK is 0, it is found that a larger stop band width can be obtained compared to the case where the duty DY2 of the second-order diffraction grating EE2 and the duty DY3 of the third-order diffraction grating EE3 are each set to the same value of 0.2.

FIG. 20 is a plan view showing the configuration of a resistive layer of the semiconductor light emitting device according to the eighth embodiment.
In Fig. 20, the semiconductor laser LF includes a resistive layer RF instead of the resistive layer RE of the semiconductor laser LE of Fig. 15. Other points of the semiconductor laser LF can be configured in the same manner as the semiconductor laser LE of Fig. 15.

The resistive layer RF has an opening KF, a second-order diffraction grating EF2, and a third-order diffraction grating EF3. A waveguide layer WF is provided in the opening KF. The second-order diffraction grating EF2 and the third-order diffraction grating EF3 are provided on both sides of the waveguide layer WF along the waveguiding direction D1. The second-order diffraction grating EF2 is provided with a phase shift portion SF2, and the third-order diffraction grating EF3 is provided with a phase shift portion SF3.

Here, the semiconductor laser LF is an end face reflection type laser, and the reflection surface is formed by crystal cleavage, but the characteristics vary depending on the cleavage position. In this case, by providing a phase shift section SF2 on the second-order diffraction grating EF2 and a phase shift section SF3 on the third-order diffraction grating EF3, it is possible to improve the SMSR of the diffraction grating while dealing with the variation in characteristics depending on the cleavage position, and to improve the light emission efficiency of the desired oscillation wavelength.

In such a phase-shifted distributed feedback laser diode, it is easier to obtain a larger SMSR than a laser diode with a diffraction grating that does not have a phase-shifting portion. In addition, the threshold gain can be lowered, and the characteristics of the nitride semiconductor light-emitting device can be further improved.

The center of the phase shift section is preferably located at a distance L1 between the end face MA with the lower reflectivity and 60% to 80% of the distance (L1+L2) between the end faces MA and MB. In particular, the distance L1 from the end face MA to the center of the phase shift section is preferably set to 70% (L1:L2=7:3) of the distance (L1+L2) between the end faces MA and MB. This allows the phase shift section to be positioned at a position that coincides with the centers of the peaks, valleys, or peaks of the standing waves formed by the diffraction grating, improving the SMSR.

Furthermore, it is preferable that the length of the phase shift portion satisfies the formula λ/(4·n _eff )·(2N−1), where N is a natural number (positive integer), neff is the effective refractive index of the diffraction grating, and λ is the Bragg wavelength. This allows the phase shift portion to be disposed at positions coinciding with the centers of the peaks, valleys, or peaks of the standing waves formed by the diffraction grating, thereby improving the SMSR.

21(a) and 21(b) are diagrams showing the refractive index distribution of the diffraction grating of the semiconductor light-emitting device of the ninth embodiment. Also, FIG. 21(c) and FIG. 21(d) are diagrams showing the relationship between the phase and energy of the standing wave formed in the waveguide of the semiconductor light-emitting device of the ninth embodiment. Note that in this ninth embodiment, a combination of a third-order diffraction grating and a fifth-order diffraction grating is used instead of the combination of the second-order diffraction grating EE2 and the third-order diffraction grating EE3 of FIG. 15.

In Figures 21(a) and 21(b), the pitch of the third-order diffraction grating can be matched to three times the oscillation period of the laser light. The pitch of the fifth-order diffraction grating can be matched to five times the oscillation period of the laser light. Even in the case of a combination of a third-order diffraction grating and a fifth-order diffraction grating, the greatest common divisor of the orders of these diffraction gratings is 1, so only diffraction occurs in the in-plane direction (180°). This provides the effect of efficiently achieving stable laser oscillation.

Figure 21 (a) shows the refractive index distribution of a third-order diffraction grating, where the low refractive index portion corresponds to the concave portion of the third-order diffraction grating, and the high refractive index portion corresponds to the convex portion. Similarly, (b) shows the refractive index distribution of a fifth-order diffraction grating. In the combination of a third-order diffraction grating and a fifth-order diffraction grating, it can be seen that there are points PC21 and PC23 where the center of the concave portion of the third-order diffraction grating coincides with the center of the convex portion of the fifth-order diffraction grating, and points PC22 and PC24 where the center of the convex portion of the third-order diffraction grating coincides with the center of the concave portion of the fifth-order diffraction grating. At this time, at points PC21 and PC23 where the center of the concave portion of the third-order diffraction grating coincides with the center of the convex portion of the fifth-order diffraction grating, and points PC22 and PC24 where the center of the convex portion of the third-order diffraction grating coincides with the center of the concave portion of the fifth-order diffraction grating, the difference in amplitude between the standing waves VE3 and VE4 increases, and the difference in energy density u between the standing waves VE3 and VE4 increases. Therefore, by providing points PC21 and PC23 where the center of the concave portion of the third-order diffraction grating coincides with the center of the convex portion of the fifth-order diffraction grating, and points PC22 and PC24 where the center of the convex portion of the third-order diffraction grating coincides with the center of the concave portion of the fifth-order diffraction grating, the stop band width can be increased. As a result, the coupling coefficient between the guided light and the high-order diffraction grating can be increased.

FIG. 22 is a diagram showing the relationship between the grating shift and the stop band width when the duty of the diffraction grating of the semiconductor light emitting device according to the ninth embodiment is changed.
22, the stop band width was estimated when the duty of the third-order diffraction grating and the duty of the fifth-order diffraction grating were set to the same value and the inter-grating shift was changed between 0.1 and 0.5. Here, for the duty DY3 of the third-order diffraction grating and the duty DY5 of the fifth-order diffraction grating, the ◆ mark indicates the case of 0.1, the ■ mark indicates the case of 0.2, the ▲ mark indicates the case of 0.3, the × mark indicates the case of 0.4, and the asterisk indicates the case of 0.5.

From these results, it was found that the stop band width changes depending on the relative positions of the multiple diffraction gratings. In this estimation, the largest stop band value was obtained when the duty of the third-order diffraction grating and the duty of the fifth-order diffraction grating were 0.5 and the inter-grating shift was 0.5.

The duty of the third-order diffraction grating and the duty of the fifth-order diffraction grating may be different from each other. For example, in the case where the duty of the third-order diffraction grating is 0.5, the duty of the fifth-order diffraction grating is 0.1, and the inter-grating shift is 0.5, and in the case where the duty of the third-order diffraction grating is 0.5, the duty of the fifth-order diffraction grating is 0.3, and the inter-grating shift is 0, the stop band value was the same as that in the case where the stop band value was the largest in FIG. 22 (the duty of the third-order diffraction grating and the duty of the fifth-order diffraction grating are 0.5, and the inter-grating shift is 0.5).

FIG. 23 is a plan view showing the configuration of a resistive layer of the semiconductor light emitting device according to the tenth embodiment.
In Fig. 23, the semiconductor laser LG includes a resistive layer RG instead of the resistive layer RF of the semiconductor laser LF in Fig. 20. Other points of the semiconductor laser LG can be configured in the same way as the semiconductor laser LF in Fig. 20.

The resistive layer RG has an opening KG, second-order diffraction gratings EG2, EG2' and third-order diffraction gratings EG3, EG3' instead of the opening KE, second-order diffraction grating EE2 and third-order diffraction grating EE3 of FIG. 20.

A waveguide layer WG is provided within the opening KG. Second-order diffraction gratings EG2, EG2' and third-order diffraction gratings EG3, EG3' are located on both sides of the waveguide layer WG along the waveguiding direction L1. In this case, the third-order diffraction gratings EG3, EG3' can be arranged closer to the waveguide layer WG than the second-order diffraction gratings EG2, EG2'. This allows the high-order diffraction gratings to be arranged closer to the light distribution of the emitted light, and the low-order diffraction gratings to be arranged farther from the light distribution. Therefore, the coupling coefficients of the low-order diffraction gratings and the high-order diffraction gratings can be made roughly the same, and the emitted light can be efficiently diffracted in the 180° direction.

FIG. 24 is a diagram showing the relationship between the height of the diffraction grating and the coupling coefficient.
In FIG. 24, according to the literature (IEEE J. Quantum Electron. QE-11, p867, 1975), the coupling coefficient decreases even if the height of the diffraction grating is the same as the order number. By using a method similar to that shown in this literature, the coupling coefficients of diffraction gratings of different orders were estimated for the case of TE mode and rectangular diffraction grating. As a result, as shown in FIG. 24, it can be seen that the coupling coefficient decreases even if the height of the diffraction grating is the same as the order number (the number represented by "m" in the figure) increases. Here, the refractive indices used to estimate the coupling coefficient were n ₁ =2.48, n ₂ =2.49, and n ₃ =2.48. In addition, the variables common to the method in this literature were guide layer thickness t=3 μm, oscillation wavelength λ ₀ =444 nm, and duty=0.4.

Figures 25 to 29 show a method for manufacturing a semiconductor light-emitting device according to the 11th embodiment. In each figure, (a) is a plan view showing the method for manufacturing a semiconductor light-emitting device according to the 11th embodiment, and (b) is a cross-sectional view cut along the waveguide direction corresponding to (a) in each figure. Note that Figures 25(b) to 27(b) and Figure 29(b) show configurations cut along line A1-A1 in the corresponding figures (a), and Figure 28(b) shows a configuration cut along line B1-B1 in Figure 28(a).

In Figures 25(a) and 25(b), an n-type nitride cladding layer 12, an n-type nitride guide layer 13, an undoped nitride guide layer 14, an active layer 15, an undoped nitride guide layer 16, a p-type carrier block layer 17, and p-type nitride guide layers 18 and 18A are sequentially stacked on an n-type nitride semiconductor substrate 11 by epitaxial growth.

26(a) and 26(b), the p-type nitride guide layer 18A is patterned based on photolithography and dry etching techniques to alternately form convex portions QT2 and concave portions QB2 in the p-type nitride guide layer 18A at a period twice the oscillation wavelength along the waveguide direction D1, and alternately form convex portions QT3 and concave portions QB3 in the p-type nitride guide layer 18A at a period three times the oscillation wavelength along the waveguide direction D1. At this time, the arrangement of the convex portions QT2 and concave portions QB2 and the arrangement of the convex portions QT3 and concave portions QB3 can be arranged adjacent to each other in the lateral direction D2 of the waveguide direction D1.

Next, as shown in Figures 27(a) and 27(b), resistive layers RH, RH' are formed sequentially on the p-type nitride guide layers 18, 18A by epitaxial growth or sputtering to form the second-order diffraction grating EH2 and the third-order diffraction grating EH3. The resistive layers RH, RH' can be formed collectively in a single film formation process. At this time, the resistive layer RH can be formed so that the recesses QB2, QB3 of the p-type nitride guide layer 18A are filled, and the resistive layer RH' can be formed so that the protrusions QT2, QT3 of the p-type nitride guide layer 18A and the resistive layer RH are covered.

Next, as shown in Figures 28(a) and 28(b), the resistive layers RH and RH' are patterned using photolithography and dry etching techniques to form openings KH and KH' in the resistive layers RH and RH' along the waveguide direction D1. At this time, the resistive layers RH and RH' are removed from the openings KH and KH', respectively, and the protrusions QT2 and QT3 and the recesses QB2 and QB3 of the p-type nitride guide layer 18' are exposed from the resistive layers RH and RH'.

Next, as shown in Figures 29(a) and 29(b), a p-type nitride guide layer 18A' is selectively formed by epitaxial growth on the p-type nitride guide layers 18, 18A and on the resistive layer RH' so as to fill the openings KH, KH'. At this time, a waveguide layer WH is formed in the opening KH, with a second-order diffraction grating EH2 and a third-order diffraction grating EH3 provided on both sides along the waveguiding direction D1. Also, a waveguide layer WH' is formed in the opening KH', without a second-order diffraction grating EH2 and a third-order diffraction grating EH3 provided on both sides.

Next, the p-type nitride cladding layer 20 and the p-type nitride contact layer 21 are sequentially formed on the p-type nitride guide layer 18A' by epitaxial growth.

This makes it possible to arrange the second-order diffraction grating EH2 and the third-order diffraction grating EH3 close to the active layer 15 while laterally confining the guided light guided through the active layer 15 based on a single film formation process of the resistive layers RH and RH'. Furthermore, it is possible to narrow the current injected into the active layer 15 at the position of the opening KH' while ensuring the refractive index difference between the p-type nitride guide layer 18A and the second-order diffraction grating EH2 and the third-order diffraction grating EH3. This makes it possible to increase the coupling coefficient between the guided light and the second-order diffraction grating EH2 and the third-order diffraction grating EH3, while suppressing the heat generation of the semiconductor laser and lowering the threshold current of the semiconductor laser. As a result, it is possible to stabilize the oscillation wavelength while enlarging the pitch compared to the first-order diffraction grating, and to increase the output while ensuring the reliability of the semiconductor laser.

Figures 30(a) to 33(a) are plan views showing a method for manufacturing a semiconductor light-emitting device according to the twelfth embodiment, and Figures 30(b) to 33(b) are cross-sectional views cut along the waveguide direction of Figures 30(a) to 33(a), respectively. Note that Figures 30(b) to 33(b) show configurations cut along lines A1-A1 of Figures 30(a) to 33(a), respectively.

30(a) and 30(b), an n-type nitride cladding layer 12, an n-type nitride guide layer 13, an undoped nitride guide layer 14, an active layer 15, an undoped nitride guide layer 16, a p-type carrier block layer 17, and a p-type nitride guide layer 18 are sequentially stacked on an n-type nitride semiconductor substrate 11 by epitaxial growth. Furthermore, a resistive layer RI is stacked on the p-type nitride guide layer 18 by a method such as epitaxial growth or sputtering.

Next, as shown in Figures 31(a) and 31(b), the resistive layer RI is patterned using photolithography and dry etching techniques to form an opening KI in the resistive layer RI, with a second-order diffraction grating EI2 and a third-order diffraction grating EI3 on either side along the waveguide direction D1.

Next, as shown in Figures 32(a) and 32(b), a p-type nitride guide layer 18A is selectively formed on the p-type nitride guide layer 18 by epitaxial growth so as to be embedded in the opening KI. At this time, the p-type nitride guide layer 18A can be embedded in the recesses of the second-order diffraction grating EI2 and the recesses of the third-order diffraction grating EI3, and the refractive index difference between the recesses and protrusions of the second-order diffraction grating EI2 and the refractive index difference between the recesses and protrusions of the third-order diffraction grating EI3 can be determined by the refractive index of the resistive layer RI. In addition, a waveguide layer WI is formed in the opening KI, with the second-order diffraction grating EI2 and the third-order diffraction grating EI3 provided on both sides along the waveguiding direction D1.

Next, as shown in Figures 33(a) and 33(b), a p-type nitride cladding layer 20 and a p-type nitride contact layer 21 are sequentially formed on the p-type nitride guide layer 18A by epitaxial growth.

This makes it possible to form the second-order diffraction grating EI2 and the third-order diffraction grating EI3 on both sides of the waveguide layer WI at the same time as forming the waveguide layer WI in the opening KI. It also makes it possible to increase the refractive index difference between the p-type nitride guide layer 18A and the second-order diffraction grating EI2 and the third-order diffraction grating EI3. This makes it possible to stably form an inner stripe type semiconductor laser having a DFB structure with an expanded pitch compared to a first-order diffraction grating while suppressing an increase in the number of steps.

E1 n-type nitride semiconductor layer E2 p-type nitride semiconductor layer E3 Confinement layer 11 n-type nitride semiconductor substrate 12 n-type nitride cladding layer 13 n-type nitride guide layer 14, 16 Undoped nitride guide layer 15 Active layer 17 p-type carrier block layer 18 p-type nitride guide layer RA Resistance layer 20 p-type nitride cladding layer 21 p-type nitride contact layer

Claims (17)

A first conductivity type semiconductor layer;
an active layer provided on the first conductive type semiconductor layer;
a second conductive type semiconductor layer provided on the active layer;
a waveguide layer provided in the second conductive type semiconductor layer, for guiding the guided light while confining the guided light in a lateral direction of a guide direction of the guided light in the active layer;
a diffraction grating provided in the second conductive type semiconductor layer along a guide direction of the guided light;
a confinement layer provided on the waveguide layer and the diffraction grating , for vertically confining guided light guided through the active layer,
the grating comprises a resistive layer;
the resistive layer is located in a portion of the second conductive type semiconductor layer, and has a smaller refractive index and a larger resistance than the second conductive type semiconductor layer;
The semiconductor light emitting device is characterized in that the diffraction grating is located on both sides of the waveguide layer . The semiconductor light-emitting element according to claim 1, characterized in that the confinement layer is a second conductivity type semiconductor layer having a smaller refractive index than the waveguide layer. The semiconductor light-emitting device according to claim 1, characterized in that the confinement layer is a transparent conductive layer that is transparent to the guided light that guides the active layer. The semiconductor light-emitting device according to claim 1, characterized in that the confinement layer is used as at least one of a guide layer and a cladding layer on the active layer. 2. The semiconductor light emitting device according to claim 1, wherein the diffraction grating is set back from an end face of the active layer by a distance equal to or greater than the period of the diffraction grating. The semiconductor light-emitting device according to claim 1, characterized in that the diffraction grating has a phase shift portion. The semiconductor light-emitting element according to claim 6, characterized in that the length of the phase shift portion satisfies the relationship of λ/(4·n _eff )·(2N-1), where N is a positive integer, n eff _is an effective refractive index of the diffraction grating, and λ is the Bragg wavelength. 7. The semiconductor light emitting device according to claim 6 , wherein the center of the phase shift portion is located at a distance between 60% and 80% of the distance between the end face having a lower reflectance and the end face of the active layer. The semiconductor light-emitting device according to claim 1, characterized in that the condition 1≦κ·L≦3 is satisfied, where κ is the coupling coefficient of the diffraction grating and L is the resonator length. The semiconductor light-emitting device according to claim 1, characterized in that the waveguide layer is made of GaN and the diffraction grating is made of AlN. The semiconductor light-emitting device according to claim 1, characterized in that the diffraction grating comprises a plurality of high-order diffraction gratings having a greatest common denominator of 1 and different orders. The semiconductor light-emitting element according to claim 11, characterized in that the multiple high-order diffraction gratings have areas in which at least one of the centers of the convex portions and the centers of the concave portions and the centers of the convex portions and the concave portions coincide with each other . The semiconductor light emitting device according to claim 11 , wherein the duties of the multiple high-order diffraction gratings are different from each other. The semiconductor light emitting device according to claim 11 , wherein the plurality of high-order diffraction gratings are arranged so that the coupling coefficients are equal to each other. A first conductivity type semiconductor layer;
an active layer provided on the first conductive type semiconductor layer;
a second conductive type semiconductor layer provided on the active layer;
a waveguide layer provided in the second conductive type semiconductor layer, for guiding the guided light while confining the guided light in a lateral direction of a guide direction of the guided light in the active layer;
a diffraction grating provided in the second conductive type semiconductor layer along a guide direction of the guided light;
a confinement layer provided on the waveguide layer and the diffraction grating, for vertically confining guided light guided through the active layer,
the grating comprises a resistive layer;
the resistive layer is located in a portion of the second conductive type semiconductor layer, and has a smaller refractive index and a larger resistance than the second conductive type semiconductor layer;
The resistive layer is
a first resistive layer in which the diffraction grating is formed on both sides of a first opening in which the waveguide layer is embedded;
a second resistive layer laminated on the first resistive layer, the second resistive layer having a second opening in which the waveguide layer is embedded. a step of sequentially stacking an active layer and a second conductive type semiconductor layer on the first conductive type semiconductor layer;
forming projections and recesses on the second conductive type semiconductor layer;
a step of laminating a resistive layer having a smaller refractive index and a larger resistance than the second conductive type semiconductor layer on the second conductive type semiconductor layer so as to cover the irregularities, thereby forming a diffraction grating fitted to the irregularities;
forming an opening in the resistive layer on which the diffraction grating is formed;
and re-growing the second conductive type semiconductor layer so as to fill the opening. a step of sequentially stacking an active layer, a second conductive type semiconductor layer, and a resistive layer having a resistance higher than that of the second conductive type semiconductor layer on a first conductive type semiconductor layer;
forming an aperture in the resistive layer flanked by a diffraction grating;
and re-growing the second conductive type semiconductor layer so that the diffraction grating and the opening are buried.