JP4155664B2 - Semiconductor laser device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a laser device made of a semiconductor material.
[0002]
[Prior art]
Semiconductor laser devices are widely used in the information industry such as optical communication and optical recording, and their cost reduction and high performance are required. The semiconductor laser device has an active layer that emits light and a layer that confines the emitted light in the vicinity of the active layer, and includes the active region that amplifies the light including these layers and feedback necessary for oscillation. A resonator having a reflection structure to be generated is formed, and emitted light is emitted as laser light. The active region and the resonator have an elongated structure in the light emission direction. In a semiconductor laser device, a resonator is arranged in parallel with a substrate surface, an edge-emitting type that emits laser light from an end surface perpendicular to the substrate surface, and a resonator is formed perpendicular to the substrate surface, and the direction perpendicular to the substrate There is a surface emitting type that emits laser light. In the edge-emitting type, the current to be injected flows across the resonator. In the surface-emitting laser, the current flows through the resonator in the longitudinal direction, and a predetermined current injection region that defines the active region is set. .
[0003]
The edge-emitting type further includes a Fabry-Perot laser having a reflecting structure with reflecting surfaces at both ends, and a reflecting structure with a number of distributed reflecting surfaces provided inside. There is a distributed feedback type.
[0004]
Embedded type lasers have been widely used as edge-emitting lasers. Recently, ridge-type semiconductor laser devices have been proposed [US document "IEEE Photonics Technology Letters", Vol. 7, Vol. 1 (issued January 1995), pages 13-15]. The ridge type is intended to reduce the cost of the edge-emitting laser, and has a ridge structure in which an upper clad layer that is a part of the optical confinement layer protrudes from the substrate surface. The ridge structure is designed to have a predetermined current injection region immediately below it, and has an elongated stripe shape. In the semiconductor laser device having the ridge structure, the active layer is formed on the entire surface of the substrate. However, since the current injection region is limited by the ridge structure, an effective active layer region is set.
[0005]
In the manufacturing process of the semiconductor laser device, the buried type requires crystal growth of about three times, whereas the ridge type requires only one crystal growth, so that the process becomes simple and the cost can be reduced. Become. However, the ridge type has a drawback that the threshold current is larger than that of the buried type. The threshold current increases because the current injected through the ridge structure diffuses laterally beyond a predetermined current injection region. The diffusion spreads as the current approaches the substrate.
[0006]
In order to prevent such current diffusion, a ridge type has been proposed in which hydrogen ions are implanted into a part of the cladding layer to increase the resistance of the part (see, for example, Japanese Patent Laid-Open No. 10-229246). In this case, as shown in FIG. 8, first, the active layer 1 is formed on the lower clad layer 12 formed on the entire surface of the substrate 5, and further the upper clad layer 4 is formed on the entire surface, and then the ridge structure. Then, the upper surface of the ridge waveguide 20 is masked, and hydrogen ions are implanted into the side surface of the ridge waveguide 20 and the upper surface of the cladding layer 4. In this case, hydrogen ions are implanted shallowly so as not to reach the active layer 1, and only the shallow layer 21 on the side surface of the ridge waveguide 20 and the upper surface of the cladding layer 4 is increased in resistance. Although the diffusion of current is blocked to some extent by the high resistance layer 21, there is no structure for suppressing the diffusion of current after passing through the high resistance portion, and there is a problem that the effect of blocking current diffusion is insufficient. It was.
[0007]
On the other hand, the diffusion of the injection current in the lateral direction becomes a problem also in the case of a surface emitting laser. As a countermeasure, an oxidation that restricts the current flow range in the middle of the upper cladding layer to the central portion There are proposals to provide a layer. However, this method has a problem that not only the manufacturing process is complicated and the cost is increased, but also the effect of suppressing current diffusion is not sufficient as described above.
[0008]
[Problems to be solved by the invention]
In order to enhance the effect of blocking current diffusion, it is desirable to introduce the impurity deeply so as to reach the active layer, instead of introducing it as shallow as described above. However, since ion implantation has a defect of damaging a wide range of crystals, there is a problem in reliability in ion implantation reaching the active layer. FIG. 9 shows the reliability test results of the semiconductor in which hydrogen ions are implanted up to the active layer. In this test, the rate of change in operating current compared to the initial state was measured when the laser drive circuit was controlled so that the optical output was constant at 5 mW at an environmental temperature of 85 ° C. Generally, the time when the change rate of the operating current exceeds 20% is defined as the lifetime. As shown in FIG. 9, the semiconductor laser ion-implanted to the active layer has a change rate of the operating current exceeding 20% in 45 hours, and does not reach the normal practical life time of 10,000 hours or more. . This rapid decrease in deterioration is thought to be due to the semiconductor crystal being damaged by ion implantation.
[0009]
The object of the present invention is to solve the above-mentioned problems of the prior art, and to propose a novel semiconductor laser device that lowers the threshold current by effectively suppressing the diffusion of the injected current in the lateral direction and that is low in cost. There is.
[0010]
[Means for Solving the Problems]
The most significant feature of the present invention is an edge emitting semiconductor laser device having an active layer, a light confinement layer, and a reflection structure for causing laser oscillation on a substrate, and the upper light confinement layer forms a ridge structure. The active layer region is set immediately below the ridge structure by a layer in which a part of the compound semiconductor on the substrate is formed into a semi-insulating layer by impurity diffusion.
[0011]
Another feature of the present invention is that an active layer, a light confinement layer, and a reflection structure for causing laser oscillation are formed on a substrate, and the reflection structure is formed by a multilayer reflector provided above and below the active layer. In the surface emitting semiconductor laser device in which the upper multilayer reflector has a surface parallel to the substrate surface and has a protruding structure, a part of the compound semiconductor on the substrate is formed into a semi-insulating layer by impurity diffusion. According to the layer, the region of the active layer is set immediately below the upper multilayer reflector.
[0012]
Although it is known that a semiconductor is semi-insulated by introducing an impurity into the semiconductor, the present invention has been made by paying attention to the fact that diffusion causes less damage to a crystal unlike ion implantation. In other words, impurity diffusion was performed until the active layer was reached, and it was possible to surround the region immediately below the ridge structure or the upper multilayer reflector with a semi-insulating layer. By this semi-insulating layer, an active layer region is set immediately below the ridge structure or the upper multilayer reflector.
[0013]
Since no current flows through the semi-insulating layer, the injected current flows only directly under the ridge structure or the protrusion structure, and current diffusion is suppressed. That is, according to the present invention, it is possible to inject current without causing diffusion only in the active layer immediately below the ridge structure or the protrusion structure, so that the threshold current can be reduced. Such a region of the active layer becomes a predetermined current injection region.
[0014]
FIG. 9 also shows the reliability test results of the semiconductor laser of the present invention. As shown in FIG. 9, the operating current change rate of the semiconductor laser in which Fe is diffused to the active layer in the ridge structure is about 3% after 1000 hours, and the estimated lifetime is 50,000 hours or more. Estimated life time that is sufficiently practical is obtained.
[0015]
As shown in FIG. 10, the impurity concentration in the case of ion implantation is maximized inside the semiconductor, whereas the impurity concentration in diffusion is maximized on the surface and decreases in the depth direction. The difference in the structure of the semi-insulating layer is clear between ion implantation and diffusion.
[0016]
Periodic table of Fe, Cr, Ti, Ru, etc. as impurities (“Science Chronology, published by Tokyo Astronomical Observatory edited by Karasuma Zen) 1976 Group IVB, Group VIB, Group VIIB and Group VIII transition metals in) can give favorable results.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a semiconductor laser device according to the present invention will be described in more detail with reference to embodiments of the invention according to some examples using the drawings. In addition, the same symbol in FIGS. 1-8 shall display the same thing or a similar thing.
[0018]
【Example】
<Example 1>
FIG. 1 shows an embodiment in which the present invention is applied to a 1.3 μm band semiconductor laser device (hereinafter simply referred to as “semiconductor laser”) used as a transmission light source for optical communication. In the figure showing a cross-sectional structure, 5 is a p-type InP semiconductor substrate, 3 is a 0.05 μm thick p-type InGaAsP lower guide layer formed on the semiconductor substrate 5, and 1 is formed on the lower guide layer 3. A multi-quantum well active layer 2 having a thickness of 0.07 μm, which emits light at a wavelength of 1.3 μm, has five well layers made of InGaAsP and a barrier layer made of the same material filling the interlayer, and is formed on the active layer 1 An n-type InGaAs AsP upper guide layer 4 having a thickness of 0.12 μm, 4 is an n-type InP upper clad layer having a ridge structure of 1.9 μm and a width of 1.8 μm formed on the upper guide layer 2, 6 The upper guide layer 2, the active layer 1, and the lower guide layer 3 are regions for forming a current injection region immediately below the upper cladding layer 4, and a semi-insulating layer in which Fe is diffused as an impurity. The semi-insulating layer 6 is also formed on the side surface of the upper cladding layer 4 so that the current injection region and the region of the upper cladding layer 4 are continuous. In this embodiment, the semiconductor substrate 5 functions as a lower cladding layer. The lower clad layer, the lower guide layer 3, the upper guide layer 2, and the upper clad layer 4 serve as an optical confinement layer.
[0019]
Further, in FIG. 1, 7 is an n-type InGaAs contact layer having a thickness of 0.2 μm for obtaining ohmic contact, 8 is an upper electrode formed on the contact layer 7, and 9 is on the back surface of the semiconductor substrate 5. The formed lower electrode 10 is made of SiO that covers the surface of the semi-insulating layer 6. ₂ It is a protective layer.
[0020]
Next, a method for manufacturing the semiconductor laser of this embodiment will be described. First, by crystal growth by metal organic vapor phase epitaxy, a p-type InGaAsP layer serving as the lower guide layer 3 is formed on the entire surface of the semiconductor substrate 5 to a thickness of 0.05 μm, and five InGaAsAsP layers serving as the multiple quantum well active layer 1 are formed. The barrier layer of the same material has a total thickness of 0.07 μm, the n-type InGaAsP layer to be the upper guide layer 2 has a thickness of 0.12 μm, and the n-type InP layer to be the upper cladding layer 4 has a thickness of 1.7 μm. An n-type InGaAs layer to be the contact layer 7 is formed in this order in a thickness of 0.2 μm. Next, SiO ₂ A film 11 is formed, and the uppermost SiO 2 layer is formed by photolithography and etching. ₂ The cross-section of the semiconductor portion is a narrow stripe having a width of 1.8 μm and a height of 1.9 μm. The film 11 and the n-type InGaAs layer serving as the contact layer 7 below it and the n-type InP layer serving as the upper cladding layer 4 therebelow. To be processed.
[0021]
Next, PH is used at 500 ° C. using a metal organic chemical vapor deposition reactor. _Three And H ₂ Fe (C in the atmosphere _Five H _Five ) ₂ This is performed by vapor phase diffusion of Fe with a gas. This allows Fe (C _Five H _Five ) ₂ The gas is decomposed by heat, and Fe atoms diffuse into the above-described layers, that is, regions other than the mask of the compound semiconductor layer. Diffusion is performed until the layer that becomes the active layer 1 is reached. At this time ₂ Since the film 11 serves as a mask, Fe atoms do not diffuse into the upper part of the ridge structure.
[0022]
Now, when Fe atoms are introduced into a compound semiconductor, a level is formed in the central part of the semiconductor band gap, so that even if electrons are injected, the electrons are trapped in the central level, so that the semiconductor is semi-insulating. Therefore, no current flows in the region where Fe is diffused. Thus, the semi-insulating layer 6 in which Fe atoms are diffused is formed as shown in FIG.
[0023]
After forming the semi-insulating layer 6, an upper electrode 8 made of metal is formed on the contact layer 7, and a lower electrode 9 made of metal is formed on the back surface of the semiconductor substrate 5. Next, the SiO which becomes the protective layer 10 on the surface of the semi-insulating layer 6 is formed by photolithography. ₂ A semiconductor laser having a Fabry-Perot laser structure having a reflecting structure having a double-sided cleavage surface as a reflection surface is formed by forming a film and finally cleaving the film at a length of 400 μm at right angles to the laser beam emission direction. Complete. Note that the length of the stripe of the ridge structure becomes 400 μm by cleavage.
[0024]
As described above, in the semiconductor laser of this embodiment, the active layer 1 is surrounded by the semi-insulating layer 6 so that its region is determined immediately below the ridge structure, and this region becomes a predetermined current active region. As described above, since no current flows through the semi-insulating layer 6, lateral electron diffusion, which is a problem in the ridge type laser, is suppressed, whereby the threshold current can be reduced.
[0025]
In FIG. 2, the three layers formed on the entire surface of the substrate 5 so as to become the upper guide layer 2, the multiple quantum well active layer 1 and the lower guide layer 3 in the region where Fe is diffused have different band gaps so as to cause laser oscillation. It is composed of a semiconductor laminated film, and in particular, the band gap of the quantum well layer is smaller than other films. When Fe is diffused in this region, mixed crystallization occurs in which the band gap is averaged depending on the temperature and the amount of diffusion. At this time, the mixed crystal region has a band gap larger than that of the quantum well layer due to the averaging of the band gap, and the absorption of light by the laser beam is lost. Therefore, the threshold current is further reduced and the efficiency is increased. In addition, the effect of semi-insulating is great because the band gap is large.
[0026]
In this example, the average impurity concentration in the region where Fe atoms are diffused is about 5 × 10 5. ¹⁷ cm ^-3 And the resistivity is 7 × 10 ⁸ Good semi-insulating properties were obtained with Ωcm. Further, by setting the conditions of temperature and diffusion amount, mixed crystallization was caused in this diffusion region. A Fabry-Perot laser having a cavity length of 400 μm with a double-sided cleaved surface as a reflecting surface, which effectively suppresses lateral diffusion of the injected current due to the semi-insulating characteristics in the Fe introduction region, and lowers the threshold current due to mixed crystallization. In the semiconductor laser of this example, a low threshold current of 3.4 mA could be obtained. Further, even at a high temperature of 85 ° C., the low threshold current was 8.5 mA. Since the semi-insulating region is formed by diffusion, the damage to the crystal is small, and the estimated lifetime at 85 ° C. is 1.8 × 10 6. ^Five Time and high reliability were obtained.
[0027]
Further, in this embodiment, since the general process technique described above is employed for forming the semi-insulating layer 6, the low cost characteristic inherent in the ridge structure laser can be maintained.
[0028]
In this embodiment, Fe is used to form the semi-insulating layer 6. However, the present invention is not limited to this, and the groups IVB and VIB in the periodic table such as Cr, Ti, and Ru are used. , Group VIIB and Group VIII transition metals or combinations thereof can be employed, and similar effects can be obtained. In addition, the ridge structure has the same shape in the cross section such as parallel to the substrate, but it can be a reverse mesa structure in which the cross-sectional area increases toward the top. Further, in the active layer 1, the barrier layer is made of the same material as the well layer, but the barrier layer can be a layer made of InGaAlAs.
[0029]
<Example 2>
FIG. 3 shows an embodiment in which the present invention is applied to a 1.55 μm band semiconductor laser used as a transmission light source for optical communication. In the figure showing the cross-sectional structure, 12 is an n-type InAlAs lower cladding layer having a thickness of 0.2 μm provided between the active layer 1 and the semiconductor substrate 5, and 13 is an active layer 1 and an upper cladding layer 4. A p-type InAlAs upper cladding layer having a thickness of 0.2 μm and forming a part of a ridge structure having a width of 1.5 μm provided therebetween. Here, the layer 4 is referred to as a second upper cladding layer, and the layer 13 is referred to as a first upper cladding layer.
[0030]
In the present embodiment, the semi-insulating layer 6 is formed by diffusing Fe as an impurity in three layers formed on the entire surface of the substrate 5 to be the upper guide layer 2, the active layer 1, and the lower guide layer 3. Unlike the case of Example 1, it is not formed on the side surface of the ridge structure. Due to the semi-insulating layer 6, the region of the active layer 1 becomes a current injection region immediately below the second upper cladding layer 4 and the first upper cladding layer 13.
[0031]
The active layer 1 is a multi-quantum well active layer having a thickness of 0.08 μm, which has seven well layers made of InGaAlAs and a barrier layer made of the same material filling the interlayer, and emits light at a wavelength of 1.55 μm. The substrate 5 is an n-type InP semiconductor substrate, the lower guide layer 3 is an n-type InGaAlAs layer having a thickness of 0.05 μm, the upper guide layer 2 is an undoped (having no impurities) InGaAsP layer having a thickness of 0.05 μm, (2) The upper cladding layer 4 is a p-type InP layer having a thickness of 1.3 μm, and the contact layer 7 is a p-type InGaAs layer having a thickness of 0.2 μm. The first upper cladding layer 13, the second upper cladding layer 4, and the contact layer 7 form a ridge structure having a thickness of 1.7 μm and a width of 1.5 μm. Others are the same as in the second embodiment. With the above structure, the lower clad layer 12, the lower guide layer 3, the upper guide layer 2, the first upper clad layer 13 and the second upper clad layer 4 serve as an optical confinement layer.
[0032]
Next, a method for manufacturing the semiconductor laser of this embodiment will be described. The steps up to the formation of the ridge structure are the same as in the case of Example 1, and each layer is formed by crystal growth by metal organic vapor phase epitaxy.
[0033]
Unlike the first embodiment, the next Fe diffusion step is performed on the side surface of the ridge structure as shown in FIG. ₂ A mask film is applied so that Fe diffusion to the side surface of the ridge structure does not occur. The mask structure for forming this self-alignment (self-alignment) can be easily realized by a dry etching technique. Diffusion is performed until the layer that becomes the diffusion layer 1 is reached, as in the first embodiment.
[0034]
In this example, a p-type semiconductor ridge structure was formed using Zn as an impurity. The laser structure in which Fe diffusion in this embodiment is limited to the three-layer region is effective for a ridge structure made of a p-type semiconductor using Zn as an impurity. That is, since Fe and Zn easily diffuse each other, if Fe is diffused into a p-type semiconductor using Zn, the diffusion distance becomes long, and it becomes difficult to obtain a predetermined thickness of the semi-insulating layer. is there.
[0035]
In this example, Fe atoms were diffused at 450 ° C. using a metal organic vapor phase growth apparatus. As a result, an average of about 8 × 10 ¹⁷ cm ^-3 Impurity concentration and resistivity of 9 × 10 ⁸ Good semi-insulating properties of Ωcm were obtained. This semi-insulating property of the Fe introduction region effectively suppresses the lateral diffusion of the injection current, and the reflection structure having a double-sided cleaved surface as a reflective surface is a resonator Fabry-Perot laser having a length of 400 μm. In the semiconductor laser, a low threshold current of 3.2 mA could be obtained. Further, even at a high temperature of 85 ° C., the low threshold current is 8.1 mA, and the estimated lifetime at this temperature is 1.1 × 10 6. ⁶ Time and high reliability were obtained.
[0036]
In addition, the present embodiment can maintain the low-cost characteristics inherent to the ridge structure laser as in the first embodiment.
[0037]
In the first and second embodiments, the Fabry-Perot type semiconductor laser having a resonator using the cleavage plane is taken up. However, the present invention is not limited to this, and can be applied to other types of semiconductor lasers and related devices. For example, in addition to a distributed feedback semiconductor laser or a distributed feedback semiconductor laser with oscillation wavelength control, a semiconductor laser integrated with an electroabsorption modulator, a semiconductor laser integrated with a mode expander of emitted light, and a resonator The present invention can be applied to a semiconductor optical amplifier having no structure.
[0038]
An oscillation wavelength control distributed feedback semiconductor laser has a distributed feedback reflection structure, and has a window structure in which a laser beam having a wavelength shorter than the emission wavelength is irradiated near the lower side of the ridge structure. This is a semiconductor laser device having a structure capable of controlling.
[0039]
An electroabsorption modulator has almost the same structure as a semiconductor laser, and a layer corresponding to an active layer becomes a layer that absorbs light when a reverse bias is applied, and a light transmission layer when no voltage is applied. Is used to modulate the laser beam. It can be formed on the same substrate together with the semiconductor laser. The mode expander is formed with a portion in which the cross-sectional area of the active region is reduced near the end face in the vicinity of the end facet type end face, and thus is manufactured simultaneously with the semiconductor laser.
[0040]
<Example 3>
FIG. 5 shows an embodiment in which the present invention is applied to a 0.85 μm band surface emitting semiconductor laser. In the figure showing the cross-sectional structure, reference numeral 14 denotes a lower semiconductor multi-layer reflecting mirror composed of 24.5 pairs of n-type AlAs / GaAlAs disposed between the semiconductor substrate 5 and the lower guide layer 3, and 15 denotes a p-type AlAs / GaAlAs. 22 pairs of upper semiconductor multilayer reflecting mirrors 16, 16 are semiconductor multilayer films having the same structure as the upper reflecting mirror 15.
[0041]
The upper reflecting mirror film 15 has a structure in which a cross section parallel to the substrate has a square shape of 5 μm × 5 μm and protrudes from the substrate surface, and the semiconductor multilayer film 16 is disposed with a gap in the outer peripheral portion of the upper reflecting mirror 15. The
[0042]
In this embodiment, the semi-insulating layer 6 is formed by diffusing Cr as an impurity in the semiconductor region exposed in the gap. Due to the semi-insulating layer 6, the regions of the upper guide layer 2, the active layer 1 and the lower guide layer 3 become current injection regions immediately below the upper reflecting mirror 15. The active layer 1 is a multi-quantum well active layer having a thickness of 0.04 μm, which has three well layers made of GaAs and a barrier layer made of GaAlAs filling the interlayer, and emits light at a wavelength of 0.85 μm. In addition, the substrate 5 is an n-type GaAs semiconductor substrate, the lower guide layer 3 is an n-type GaAlAs layer having a thickness of 0.1 μm, the upper guide layer 2 is a p-type GaAlAs layer having a thickness of 0.1 μm, and the upper electrode 8 is an upper portion. The lower electrode 9 is formed on the reflecting mirror 15, and is formed on the back surface of the substrate 5. With the above structure, the lower reflecting mirror 14, the lower guide layer 3, the upper guide layer 2, and the upper reflecting mirror 15 serve as a light confinement layer.
[0043]
Next, a method for manufacturing the semiconductor laser of this embodiment will be described. Layers to be the lower reflector 14, the lower guide layer 3, the active layer 1, the upper guide layer 2, and the upper reflector 15 are formed in this order on the substrate 5 by crystal growth by metal organic vapor phase epitaxy. Next, the gap is formed in a layer that becomes the upper reflecting mirror 15 by photolithography and etching. Thereby, the rectangular upper reflecting mirror 15 and the semiconductor multilayer film 16 are formed. Since these two are formed in the same process, the height is the same. Subsequently, the side surface of the upper reflecting mirror 15 and the surface of the semiconductor multilayer film 16 are made of SiO. ₂ The protective film 10 is formed.
[0044]
Next, as shown in FIG. 6, the upper surface of the upper reflecting mirror 15 is made of SiO serving as a mask. ₂ The insulating film 11 is formed, and then Cr atoms are diffused at 450 ° C. using a Cr organic compound gas using a metal organic vapor phase growth apparatus. The diffusion is performed until reaching the layer that becomes the active layer 1. In this embodiment, the region other than the semiconductor surface in the semi-insulating layer 6 is made of SiO. ₂ Since it is covered with the insulating films 10 and 11, Cr atoms efficiently gather on the semiconductor surface in the region of the semi-insulating layer 6 during diffusion and can be diffused in a short time. In this case, the semiconductor multilayer film 16 is used only for limiting the Cr atom diffusion region to the gap, and has no effect on the semiconductor laser.
[0045]
Thus, it goes without saying that the method of limiting the region in which the metal atoms are diffused to a range in which a sufficient effect for suppressing the current diffusion in the lateral direction can be obtained can be applied to the semiconductor lasers of the first and second embodiments. . Conversely, unlike the first and second embodiments, the semiconductor multilayer film 16 is not provided, and the surface emitting laser can have a structure in which impurities are diffused using only the protrusion structure as a mask. In the present embodiment, the upper reflecting mirror film 15 has a square cross-sectional shape. However, the upper reflecting mirror film 15 is not limited to this, and may have a protruding structure with a flat top portion in a rectangular, circular or other cross-sectional shape.
[0046]
The semi-insulating layer 6 of this example has an average of about 1 × 10 ¹⁸ cm ^-3 The impurity concentration is 1.2 × 10 ⁶ Good semi-insulating properties such as Ωcm were obtained. The manufactured surface emitting semiconductor laser oscillated at a low threshold current of 0.7 mA at room temperature, and the threshold current increased to 0.82 mA at 85 ° C., and the increase was small. Further, in the 85 ° C., 2 mW constant light output operation life test, no deterioration was observed even after 3000 hours, and an extremely high reliability was obtained with an estimated life of 30,000 hours.
[0047]
In this embodiment, the reflecting mirrors 15 and 14 are formed of a semiconductor multilayer film. However, the present invention is not limited to this, and a combination of a semiconductor multilayer film and a dielectric multilayer film can be used.
[0048]
<Example 4>
An example in which the emission wavelength 1.55 μm band of Example 2 is changed to the 1.3 μm band will be described below. The structure is almost the same as in FIG. In this embodiment, the substrate 5 is an n-type GaAs semiconductor substrate, the lower cladding layer 12 is an n-type GaAs layer having a thickness of 1 μm, the guide layer 3 is an n-type GaAs layer having a thickness of 0.15 μm, and the active layer 1 is a GaInNAs layer. A multi-quantum well active layer having a thickness of 0.04 μm that emits light at a wavelength of 1.3 μm and an upper guide layer 2 having a thickness of 0.1 μm. The undoped GaAlAs layer and the semi-insulating layer 6 are formed by diffusing Cr as an impurity in three layers formed on the entire surface of the substrate 5 to be the upper guide layer 2, the active layer 1 and the lower guide layer 3. The upper clad 13 is a 1.6 μm thick p-type GaAs layer, the second upper clad layer 4 is a 0.1 μm thick p-type GaAs layer, and the contact layer 7 is a 0.1 μm thick p-type GaAs layer. The first upper clad 13, the second upper clad layer 4 and the contact layer 7 form a ridge structure having a thickness of 1.8 μm and a width of 1 μm. Others are the same as in the second embodiment.
[0049]
Similar to the second embodiment, the semi-insulating layer 6 is not formed on the side surface of the ridge structure, and the region of the active layer 1 is a current injection region immediately below the second upper cladding layer 4 and the first upper cladding layer 13. It is formed to become.
[0050]
The steps up to Cr diffusion are the same as in the second embodiment. In the diffusion step for forming the semi-insulating layer 6, Cr atoms were diffused at 520 ° C. using a Cr organic compound gas in this example using a metal organic vapor phase growth apparatus. As a result, the semi-insulating layer 6 has an average of about 3 × 10 10. ¹⁷ cm ^-3 The resistivity is 3 × 10 ⁸ Good semi-insulating properties such as Ωcm were obtained. Reflecting the good semi-insulating characteristics of the Cr impurity introduction region, the lateral diffusion of the injection current is effectively suppressed, and a Fabry-Perot laser having a cavity length of 400 μm with a double-sided cleavage surface as a reflection surface is used. In the semiconductor laser, a low threshold current of 2.8 mA could be obtained. Reflecting a large conduction band gap between the GaInNAs semiconductor and GaAs, the threshold current is 4.1 mA even at a high temperature of 85 ° C., and the estimated lifetime at this temperature is 3.9 × 10 6. ^Five Time and high reliability were obtained.
[0051]
<Example 5>
An embodiment in which the present invention is applied to a blue-emitting semiconductor laser is shown in FIG. In the figure of the sectional structure, reference numeral 17 denotes a sapphire substrate. In this embodiment, the lower cladding layer 12 is an n-type AlGaN layer having a thickness of 1 μm formed on the sapphire substrate 17, the lower guide layer 3 is an n-type InGaN layer having a thickness of 0.2 μm, and the active layer 1 is , Having a multi-layer well layer made of InGaN and a barrier layer made of the same material filling the interlayer, a multi-quantum well active layer having a thickness of 0.05 μm that emits blue light, and an upper guide layer 2 having a thickness of 0.2 μm The p-type InGaN layer, the upper cladding layer 4 are p-type AlGaN with a thickness of 2 μm, the contact layer 7 is a p-type GaN layer with a thickness of 0.2 μm, and the upper cladding layer 4 and the contact layer 7 have a thickness of 2.2 μm. A ridge structure having a width of 1.5 μm is formed.
[0052]
Further, in this embodiment, the semiconductor layer 18 having the same structure as that of the cladding layer 4 is provided in a part of the peripheral portion of the cladding layer 4. Since these two are formed in the same process, they have the same height. A gap is provided between the cladding layer 4 and the semiconductor layer 18, and the semi-insulating layer 6 is formed by diffusing Fe as an impurity in the semiconductor region exposed in the gap. Due to the semi-insulating layer 6, the region of the active layer 1 becomes a current injection region immediately below the upper cladding layer 4. The protective layer 10 is formed on the side surface of the ridge structure and the surface of the semiconductor layer 18.
[0053]
Further, since the sapphire substrate 17 is an insulator, a part of the upper surface of the substrate is etched until it reaches the lower cladding layer 12, and the lower electrode 9 is formed on the exposed lower cladding layer 4. Thereby, electrical contact between the lower electrode 9 and the lower cladding layer 4 can be established. The upper electrode 8 is formed on the contact layer 7. With the above structure, the lower clad layer 12, the lower guide layer 3, the upper guide layer 2, and the upper clad layer 4 serve as an optical confinement layer.
[0054]
In the diffusion step for forming the semi-insulating layer 6, in this example, Fe atoms were diffused at 700 ° C. using a metal organic vapor phase growth apparatus. As a result, the semi-insulating layer 6 has an average of about 3 × 10 10. ¹⁷ cm ^-3 The resistivity is 3 × 10 ⁸ Good semi-insulating properties such as Ωcm were obtained. Reflecting this semi-insulating characteristic of the Fe impurity introduction region, the lateral diffusion of the injection current is effectively suppressed, and the blue of this embodiment is a Fabry-Perot laser having a resonator length of 800 μm and a double-sided cleavage surface as a reflection surface. In the semiconductor laser, a low threshold current of 25 mA could be obtained. Further, even at a high temperature of 70 ° C., the low threshold current is 53 mA, and the estimated lifetime at this temperature is 1.5 × 10 10. ^Five Time and high reliability were obtained.
[0055]
In addition, although the board | substrate was sapphire, it is not restricted to this, A GaN board | substrate can be used.
[0056]
【The invention's effect】
According to the present invention, since the lateral diffusion of the injection current is effectively suppressed, the threshold current can be greatly reduced, and furthermore, a semi-insulating layer can be formed by a simple manufacturing process. A low-cost semiconductor laser can be realized. Further, since the diffusion depth is small because it diffuses in the ridge shape, and therefore the lateral spread of the diffusion is small, a semiconductor laser excellent in active layer width control can be realized.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view for explaining a first embodiment of a semiconductor laser device according to the present invention.
FIG. 2 is a cross-sectional view for explaining a manufacturing process of the first embodiment.
FIG. 3 is a cross-sectional view for explaining second and fourth embodiments of the present invention.
FIG. 4 is a cross-sectional view for explaining a manufacturing process of a second embodiment.
FIG. 5 is a sectional view for explaining a third embodiment of the present invention.
FIG. 6 is a cross-sectional view for explaining a manufacturing process of the third embodiment.
FIG. 7 is a cross-sectional view for explaining a fifth embodiment of the present invention.
FIG. 8 is a cross-sectional view for explaining a conventional semiconductor laser device.
FIG. 9 is a curve diagram showing a reliability test result of a semiconductor laser.
FIG. 10 is a curve diagram showing a change in impurity concentration in the depth direction.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Multiple quantum well active layer, 2 ... Upper guide layer, 3 ... Lower guide layer, 4, 13 ... Upper clad layer, 5 ... Semiconductor substrate, 6 ... Semi-insulating layer, 7 ... Contact layer, 8 ... Upper electrode, DESCRIPTION OF SYMBOLS 9 ... Lower electrode, 10 ... Protective layer, 11 ... Mask film, 12 ... Lower clad layer, 14 ... Lower semiconductor multilayer reflector, 15 ... Upper semiconductor multilayer reflector, 16 ... Semiconductor multilayer film

Claims (16)

And a reflecting structure for causing the active layer and optical confinement layer and the laser oscillation on a substrate, an upper optical confinement layer in the semiconductor laser device of the edge-emitting forming a ridge structure was form shapes on the substrate A layer of a compound semiconductor including a layer to be the active layer, the side surface of which is a semi-insulating layer formed by doping a semi-insulating layer by doping a semi-insulating impurity into a region other than the region immediately below the ridge structure A region of the active layer in contact with the ridge structure is set immediately below the ridge structure ;
The semiconductor laser device according to claim 1, wherein the ridge structure is formed with a semi-insulating layer of a compound semiconductor on both side surfaces parallel to the laser light emission direction .   2. The semiconductor laser device according to claim 1, wherein a semiconductor layer having the same height as the ridge structure is disposed outside the ridge structure.   3. The semiconductor laser device according to claim 1, wherein the semi-insulating layer includes a structure in which a semiconductor is mixed into the semi-insulating layer.   The impurity is a metal selected from the group consisting of Group IVB, Group VIB, Group VIIB, and Group VIII transition metals in the periodic table, or a combination thereof. The semiconductor laser device according to any one of the above.   5. The semiconductor laser device according to claim 4, wherein the impurity is a metal selected from the group consisting of Fe, Cr, Ti, and Ru, or a combination thereof.   2. The substrate is made of a group III-V compound semiconductor containing In and P, and the active layer has a group III-V compound semiconductor containing In, Ga, As and P. The semiconductor laser device according to claim 5.   2. The substrate is made of a group III-V compound semiconductor containing In and P, and the active layer has a group III-V compound semiconductor containing In, Ga, Al and As. The semiconductor laser device according to claim 5.   The substrate is made of a group III-V compound semiconductor containing In and P, and the active layer is a layer having a group III-V compound semiconductor containing In, Ga, As and P, and In, Ga, Al. And a layer having a group III-V compound semiconductor containing As and the semiconductor laser device according to claim 1.   2. The substrate is made of a III-V group compound semiconductor containing Ga and As, and the active layer has a III-V group compound semiconductor containing Ga, In, N and As. The semiconductor laser device according to claim 5.   The substrate is made of a group III-V compound semiconductor containing Ga and As, and the active layer is a layer having a group III-V compound semiconductor containing Ga and As, and III containing Ga, Al and As. A semiconductor laser device according to claim 1, further comprising a layer having a −V group compound semiconductor.   6. The semiconductor laser device according to claim 1, wherein the substrate is sapphire, and the active layer includes a group III-V compound semiconductor containing In, Ga, and N. .   The substrate is a group III-V compound semiconductor containing Ga and N, and the active layer has a group III-V compound semiconductor containing In, Ga and N. 6. The semiconductor laser device according to any one of items 5.   3. The semiconductor laser device according to claim 1, wherein an electroabsorption optical modulator is integrated.   3. The semiconductor laser device according to claim 1, wherein a mode expander for emitted light is integrated.   It has a distributed feedback type reflection structure and a window structure that irradiates laser light with a wavelength shorter than the emission wavelength near the lower side of the ridge structure, and has a structure that can control the oscillation wavelength by laser irradiation. The semiconductor laser device according to claim 1, wherein the semiconductor laser device is a semiconductor laser device.   The semiconductor laser device according to claim 1, wherein the ridge structure has an inverted mesa shape.

Images