JP7639610B2 - NITRIDE SEMICONDUCTOR LIGHT EMITTING ELEMENT AND METHOD FOR MANUFACTURING NITRIDE SEMICONDUCTOR LIGHT EMITTING ELEMENT - Google Patents

Description

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

Nitride semiconductors are wide band gap materials that have attracted attention as materials that can cover a range of emission wavelengths from the ultraviolet to the visible region by changing the mixed crystal composition.

Patent Document 1 discloses a nitride semiconductor multilayer structure in which crystals are grown on a substrate having concave and convex portions on its surface. In this patent document 1, a light-emitting portion is formed above the convex portion, and a depression that is not completely filled by crystal growth is formed on the surface above the concave portion. The substrate is a non-nitride semiconductor substrate such as a sapphire substrate on which a nitride semiconductor layer is grown, and the width of the depression is narrower than the width of the concave portion.

Patent documents 2 and 3 disclose forming a depression at the boundary between the side and bottom parts in the recessed region, and forming protrusions at both ends of the hill. They disclose a nitride semiconductor light-emitting device in which a nitride semiconductor growth layer with good surface flatness can be formed on the hill by suppressing the movement of atoms and molecules, which are the raw materials for the nitride semiconductor thin film, between the hill and the recessed region due to migration or the like.

JP 2007-311833 A JP 2006-93548 A JP 2010-251773 A

However, if the height of the protrusions at both ends of the recess that connect to the flat portion is too high, the number of cracks can increase depending on the composition of the nitride semiconductor.

The object of the present invention is to provide a nitride semiconductor light-emitting device and a method for manufacturing the nitride semiconductor light-emitting device that can form a nitride semiconductor layer having a flat portion while suppressing the increase in cracks.

A nitride semiconductor light-emitting device according to one aspect of the present invention includes a nitride semiconductor substrate having a recess formed on a flat surface, a nitride semiconductor layer formed from the recess of the nitride semiconductor substrate to the flat surface and having a flat portion on the flat surface, and a protrusion formed in the nitride semiconductor layer on an end of the flat surface adjacent to the recess, and the thickness of the nitride semiconductor layer at the position of the protrusion is 1.0 to 1.2 times the thickness of the nitride semiconductor layer at the position of the flat portion.

As a result, even when protrusions are provided to improve the flatness of the flat portion of the nitride semiconductor layer, the height of the protrusions can be reduced. Therefore, even when the composition of the nitride semiconductor layer is set so that the emission wavelength is in the near-ultraviolet region, it is possible to suppress the increase in cracks while suppressing the decrease in flatness of the flat portion of the nitride semiconductor layer.

In addition, in a nitride semiconductor light-emitting device according to one aspect of the present invention, the nitride semiconductor layer has a recess that is recessed in a direction between the side surface and the bottom surface of the recess.

The inventors discovered that the periphery of the depression, which is recessed in the direction between the side and bottom surfaces of the recess, is a point where defects and dislocations are generated in a concentrated manner. Here, when the depression disappears, that is, when sufficient crystal growth has occurred on the side and bottom surfaces, defects and dislocations grow in the direction of the flat portion of the nitride semiconductor layer. However, if a depression is provided as in the present invention, dislocations and defects generated in the nitride semiconductor layer can be concentrated in the vicinity of the protrusion. This makes it difficult for dislocations and defects to reach the direction of the flat portion of the nitride semiconductor layer, improving the reliability of the nitride semiconductor light-emitting device.

In addition, according to a nitride semiconductor light-emitting device according to one aspect of the present invention, the nitride semiconductor substrate has a (0001) plane orientation and an absolute value of the off-angle in the <1-100> direction is 0.1 degrees or less.

This allows the height of the protrusions to be reduced without increasing the growth temperature of the nitride semiconductor layer, suppressing contamination during growth of the nitride semiconductor layer while also suppressing the increase in cracks.

In addition, according to a nitride semiconductor light-emitting device according to one aspect of the present invention, the absolute value of the off-angle in the <11-20> direction of the nitride semiconductor substrate is 0.4 degrees or more.

This makes it possible to improve the flatness of the flat portion of the nitride semiconductor layer, and therefore the manufacturing yield (also simply referred to as yield: the number of light-emitting elements that emit the desired laser light, expressed as a percentage, relative to the number of light-emitting elements that can be extracted from one wafer).

In addition, in a nitride semiconductor light-emitting device according to one aspect of the present invention, the nitride semiconductor layer has an inner stripe structure in which a current confinement layer is embedded within the nitride semiconductor layer.

This allows the current injected into the active layer to be narrowed while laterally confining the guided light that is guided through the active layer formed in the nitride semiconductor layer. This allows the threshold current of the nitride semiconductor light-emitting element to be reduced while suppressing heat generation from the nitride semiconductor light-emitting element, thereby enabling the output of the nitride semiconductor light-emitting element to be increased.

In addition, according to one aspect of the nitride semiconductor light-emitting device of the present invention, the nitride semiconductor layer includes at least one cladding layer made of a nitride semiconductor having an Al composition of 8% or more.

This allows the emission wavelength to be set in the ultraviolet range.

In addition, according to one aspect of the present invention, the nitride semiconductor light-emitting device has an emission wavelength of 390 nm or less.

This allows the emission wavelength to be set in the near-ultraviolet region, which has higher radiant energy, expanding the range of applications for nitride semiconductor light-emitting devices.

In addition, the nitride semiconductor light-emitting device according to one aspect of the present invention includes a defect region provided between the recess and the flat portion, the defect region having a higher density of crystal defects than the flat portion.

This makes it possible to suppress the concentration of dislocations and defects in the flat portion of the nitride semiconductor layer, thereby improving the reliability of the nitride semiconductor light-emitting device.

In addition, according to a nitride semiconductor light-emitting device according to one aspect of the present invention, the nitride semiconductor layer includes a cladding layer made of a nitride semiconductor having an Al composition of 8% or more, and an underlayer located within the cladding layer and made of a nitride semiconductor that does not contain Al, and the defect region is located across the interface between the cladding layer and the underlayer.

This reduces the distortion at the interface between the cladding layer and the underlayer in the flat portion, allowing dislocations and defects to be concentrated near the recesses. As a result, the formation of dislocations and defects in the flat portion of the nitride semiconductor layer can be suppressed.

In addition, a nitride semiconductor light-emitting device according to one aspect of the present invention includes a nitride semiconductor substrate having a (0001) plane orientation, an absolute value of the off-angle in the <1-100> direction being 0.1 degrees or less, and an absolute value of the off-angle in the <11-20> direction being 0.4 degrees or more, and a nitride semiconductor layer formed on the nitride semiconductor substrate.

This makes it possible to improve the flatness of the flat portion of the nitride semiconductor layer while suppressing the increase in cracks. This makes it possible to improve the manufacturing yield of nitride semiconductor light-emitting devices while improving their reliability.

In addition, a method for manufacturing a nitride semiconductor light-emitting device according to one aspect of the present invention includes step A of forming a recess on a flat surface of a nitride semiconductor substrate, and step B of forming a nitride semiconductor layer having a flat portion on the flat surface of the nitride semiconductor substrate and a protrusion on an end of the flat surface adjacent to the recess from the recess to the flat surface of the nitride semiconductor substrate, and in step B, a growth temperature of the nitride semiconductor layer is set so that the thickness of the nitride semiconductor layer at the position of the protrusion is 1.0 to 1.2 times the thickness of the nitride semiconductor layer at the position of the flat portion.

As a result, even when the composition of the nitride semiconductor layer is set so that the emission wavelength is in the near-ultraviolet region, it is possible to suppress an increase in the number of processes while suppressing a decrease in the flatness of the flat portion of the nitride semiconductor layer and suppressing an increase in cracks.

In one aspect of the present invention, a nitride semiconductor layer having a flat portion can be formed while suppressing the increase in cracks.

1 is a cross-sectional view showing the configuration of a semiconductor light emitting element according to a first embodiment, taken in a direction perpendicular to the optical waveguide direction. 2 is a cross-sectional view showing an example of a layer structure of the nitride semiconductor layer of FIG. 1. 2A to 2C are cross-sectional views showing the shape of the nitride semiconductor layer when the growth temperature of the nitride semiconductor layer in FIG. 1 is changed. 2 is a diagram showing the relationship between the thickness of a protruding portion relative to the thickness of a flat portion of the nitride semiconductor layer in FIG. 1 and the growth temperature of an n-type nitride cladding layer. FIG. 2 is a diagram showing the relationship between the thickness of a protruding portion relative to the thickness of a flat portion of the nitride semiconductor layer in FIG. 1 and the growth temperature of an n-type nitride cladding layer. FIG. 2 is a diagram showing the relationship between the thickness of a protrusion relative to the thickness of a flat portion of the nitride semiconductor layer in FIG. 1 and the probability of crack occurrence. FIG. FIG. 2 is a diagram showing the relationship between the thickness of the protrusion of the nitride semiconductor layer of FIG. 1 and the reliability and yield. FIG. 2 is a diagram showing the relationship between the thickness of the protrusion of the nitride semiconductor layer and the growth temperature of the n-type nitride cladding layer when the off angle of the nitride semiconductor substrate in FIG. 1 in the <1-100> direction is changed. 2 is a diagram showing the relationship between the off-angle in the <1-100> direction of the nitride semiconductor substrate of FIG. 1 and the probability of crack occurrence in the nitride semiconductor layer. 2 is a diagram showing the relationship between the off-angle in the <11-20> direction of the nitride semiconductor substrate of FIG. 1 and the yield. FIG. 7( a ) is a plan view showing the concentration positions of defects in the nitride semiconductor layer of the semiconductor light emitting element according to the second embodiment, and FIG. 7 ( b ) is a cross-sectional view showing the concentration positions of defects in the nitride semiconductor layer of the semiconductor light emitting element according to the second embodiment. 10A to 10C are plan views showing the state of defects when the growth temperature of the nitride semiconductor layer of the semiconductor light emitting device according to the second embodiment is changed. 11 is a cross-sectional view showing the configuration of a semiconductor light emitting element according to a third embodiment, taken in a direction perpendicular to the optical waveguide direction. FIG. 11 is a cross-sectional view showing the configuration of a semiconductor light emitting element according to a fourth embodiment, cut in a direction perpendicular to the optical waveguide direction. FIG. 13 is a cross-sectional view showing the configuration of a semiconductor light emitting element according to a fifth embodiment, cut in a direction perpendicular to the optical waveguide direction. 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.

FIG. 1 is a cross-sectional view showing the configuration of a semiconductor light emitting device according to a first embodiment, cut in a direction perpendicular to the optical waveguide direction.
In FIG. 1, the semiconductor laser LA includes a nitride semiconductor substrate 11 and a nitride semiconductor layer ML. 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). The nitride semiconductor substrate 11 has a (0001) plane orientation, and the absolute value of the off-angle in the <1-100> direction can be 0.1 degrees or less. The nitride semiconductor substrate 11 can have an absolute value of the off-angle in the <11-20> direction of 0.4 degrees or more. In this specification, in the notation of the plane orientation, instead of putting a bar on the number indicating a direction having a negative component, a minus sign is put before the number.

A recess UB is formed in the flat surface MH of the nitride semiconductor substrate 11. The recess UB is, for example, a groove formed on the nitride semiconductor substrate 11. The recess UB can be formed along the guiding direction of light guided through the nitride semiconductor layer ML. In this case, the guiding direction of light can be set to the [1-100] direction. The horizontal direction relative to the guiding direction of light can be set to the [11-20] direction, and the vertical direction relative to the guiding direction of light can be set to the [0001] direction.

The nitride semiconductor layer ML is formed from the recess UB to the flat surface MH of the nitride semiconductor substrate 11. The nitride semiconductor layer ML includes a light-emitting layer that generates light based on carrier recombination. The emission wavelength of the light-emitting layer can be set in the near-ultraviolet region. In this case, the composition of the light-emitting layer can be set so that the emission wavelength is 390 nm or less. The nitride semiconductor layer ML can also include at least one cladding layer made of a nitride semiconductor with an Al composition of 8% or more.

The nitride semiconductor layer ML has a flat portion PH and a protruding portion PB. The flat portion PH is located on the flat surface MH of the nitride semiconductor substrate 11. The protruding portion PB is located on an end of the flat surface MH adjacent to the recess UB. In this case, the thickness TP of the nitride semiconductor layer ML at the position of the protruding portion PB can be 1.0 to 1.2 times the thickness TH of the nitride semiconductor layer ML at the position of the flat portion PH.

The nitride semiconductor layer ML also has a depression KM within the recess UB. The depression KM is recessed in the direction between the side surface KS and the bottom surface KB of the recess UB. The shape of the depression KM is, for example, a wedge shape.

The nitride semiconductor layer ML has a ridge RG that confines the light guided through the light emitting layer in the horizontal and vertical directions. The ridge RG is located on the flat portion PH of the nitride semiconductor layer ML. The ridge RG can be formed parallel to the recess UB across the end faces of the nitride semiconductor layer ML. In this case, the semiconductor laser LA constitutes a ridge stripe type laser.

An electrode 24 is formed on the nitride semiconductor layer ML via an insulating layer 23. At this time, the top surface of the ridge RG is exposed from the insulating layer 23 and is connected to the electrode 24. An electrode 22 is formed on the back surface of the nitride semiconductor substrate 11. The electrode 22 may have, for example, a layered structure of Ti/Pt/Au. The electrode 24 may have, for example, a layered structure of Pd/Ti/Pt/Au. The insulating layer 23 may be, for example, a silicon oxide film or a silicon nitride film.

FIG. 2 is a cross-sectional view showing an example of the layer structure of the nitride semiconductor layer of FIG.
In FIG. 2, the nitride semiconductor layer ML in FIG. 1 can have a nitride semiconductor laminated structure including an active layer and a cladding layer laminated on a nitride semiconductor substrate 11 .

For example, the nitride semiconductor substrate 11 may be a GaN substrate. The nitride semiconductor layer ML may be configured with a laminated structure of an n-type GaN buffer layer 12, an n-type AlGaN first cladding layer 13, an InGaN underlayer 14, an n-type AlGaN second cladding layer 15, an n-type guide layer 16, an active layer 17, a p-type guide layer 18, a p-type carrier block layer 19, a p-type AlGaN cladding layer 20, and a p-type GaN contact layer 21. The active layer 17 may be, for example, a quantum well layer in which a well layer is sandwiched between barrier layers. Here, in order to set the emission wavelength in the near ultraviolet region, the n-type AlGaN second cladding layer 15 and the p-type AlGaN cladding layer 20 have the Al composition of AlGaN set to 8% or more.

The nitride semiconductor layer ML can be formed on the nitride semiconductor substrate 11 by epitaxial growth. The epitaxial growth may be MOCVD (Metal Organic Chemical Vapor Deposition), MBE (Molecular Beam Epitaxy), or HVPE (Hydride Vapor Phase Epitaxy).

Here, in order to suppress the increase in cracks in the nitride semiconductor layer ML, when a recess UB is provided on the flat surface MH of the nitride semiconductor substrate 11, the composition of the nitride semiconductor layer ML is set so that the emission wavelength is in the near ultraviolet region. In this case, if the height of the protrusion PB on the side of the recess UB is high, the increase in cracks in the nitride semiconductor layer ML cannot be suppressed. In this case, by setting the thickness TP of the nitride semiconductor layer ML at the position of the protrusion PB to be 1.0 to 1.2 times the thickness TH of the nitride semiconductor layer ML at the position of the flat portion PH, it is possible to suppress the increase in cracks while suppressing the decrease in flatness of the flat portion PH of the nitride semiconductor layer ML, even when the composition of the nitride semiconductor layer ML is set so that the emission wavelength is in the near ultraviolet region.

Here, the height of the protrusion PB can be reduced by increasing the growth temperature of the n-type AlGaN first cladding layer 13 and the n-type AlGaN second cladding layer 15. Therefore, even when the composition of the nitride semiconductor layer ML is set so that the emission wavelength is in the near-ultraviolet region, it is possible to suppress the decrease in the flatness PH of the flat part of the nitride semiconductor layer ML while suppressing an increase in the number of processes, and also to suppress an increase in cracks.

Furthermore, by providing a depression KM in the direction between the side surface KS and the bottom surface KB of the recess UB, dislocations and defects occurring in the nitride semiconductor layer ML can be concentrated in the vicinity of the protrusion PB. This makes it difficult for dislocations and defects to reach the direction of the flat portion PH of the nitride semiconductor layer ML, thereby improving the reliability of the semiconductor laser LA.

Figure 3 is a cross-sectional view showing the shape of the nitride semiconductor layer when the growth temperature of the nitride semiconductor layer in Figure 1 is changed. Note that Figures 3(a) to 3(c) show the cases where the growth temperatures of the n-type AlGaN first cladding layer 13 and the n-type AlGaN second cladding layer 15 in Figure 2 are set to 1150°C, 1100°C, and 1050°C, respectively.

When the growth temperature of the n-type AlGaN first cladding layer 13 and the n-type AlGaN second cladding layer 15 shown in FIG. 2 was set to 1150° C., the nitride semiconductor layer ML1 was formed on the nitride semiconductor substrate 11 as shown in FIG. 3(a). At this time, the thickness TP of the nitride semiconductor layer ML1 at the position of the protruding portion PB1 of the nitride semiconductor layer ML1 was 2.9 μm, and the thickness of the nitride semiconductor layer ML1 at the position of the flat portion was 2.72 μm. In addition, the thickness TS of the nitride semiconductor layer ML1 formed on the side surface KS of the recess UB at the position of the flat surface MH was 2.74 μm.

Similarly, when the growth temperature of the n-type AlGaN first cladding layer 13 and the n-type AlGaN second cladding layer 15 shown in FIG. 2 was set to 1100° C., the nitride semiconductor layer ML2 was formed on the nitride semiconductor substrate 11 as shown in FIG. 3(b). At this time, the thickness TP of the nitride semiconductor layer ML2 at the position of the protruding portion PB2 of the nitride semiconductor layer ML2 was 3.3 μm, and the thickness of the nitride semiconductor layer ML2 at the position of the flat portion was 2.73 μm. Furthermore, the thickness TS of the nitride semiconductor layer ML2 on the side surface KS of the recess UB at the position of the flat surface MH was 1.3 μm. Furthermore, a depression KM2 was formed in the direction between the side surface KS and the bottom surface KB of the recess UB.

Furthermore, when the growth temperature of the n-type AlGaN first cladding layer 13 and the n-type AlGaN second cladding layer 15 was set to 1050°C, the nitride semiconductor layer ML3 was formed on the nitride semiconductor substrate 11 as shown in Figure 3 (c). At this time, the thickness TP of the nitride semiconductor layer ML3 at the position of the protruding portion PB3 of the nitride semiconductor layer ML3 was 3.5 μm, and the thickness of the nitride semiconductor layer ML3 at the position of the flat portion was 2.68 μm. In addition, the thickness TS of the nitride semiconductor layer ML3 on the side surface KS of the recess UB at the position of the flat surface MH was 0.82 μm. In addition, a recess KM3 was formed in the direction between the side surface KS and the bottom surface KB of the recess UB. The recess KM3 has a shape that is more recessed than the recess KM2 shown in Figure 3 (b).

4A and 4B are diagrams showing the relationship between the thickness of the protruding portion of the nitride semiconductor layer in FIG. 1 and the growth temperature (T _g ^n-clad ) of the n-type nitride cladding layer.
4A and 4B, the height of the protruding portion PB could be reduced by increasing the growth temperature T _g ^n-clad of the n-type AlGaN first cladding layer 13 and the ^n- type AlGaN second cladding layer 15. For example, in the examples of FIGS. 3(a) to 3(c), the ratio of the total layer thickness of the protruding portion PB to the total layer thickness of the flat portion PH could be reduced to 1.2 times or less by setting the growth temperature T _g n-clad to 1100° C. or higher.

Fig. 5A shows the relationship between the thickness of the protruding portion of the nitride semiconductor layer in Fig. 1 and the probability of crack occurrence, and Fig. 5B shows the relationship between the thickness of the protruding portion of the nitride semiconductor layer in Fig. 1 and the reliability and yield. The off angle θ _m ^<1-100> in the <1-100> direction of the nitride semiconductor substrate 11 was set to 0.32°. The probability of crack occurrence is the probability that one or more cracks exist in a laser element of 800 μm × 400 μm.

In Figures 5A and 5B, by setting the ratio of the total layer thickness of the protruding portion PB to the total layer thickness of the flat portion PH to 1.2 times or less, it is possible to reduce cracks that occur in the nitride semiconductor layer ML. This makes it possible to improve the manufacturing yield of the semiconductor laser LA while also improving its reliability. In this case, the mean time to failure (MTTF) of the semiconductor laser LA can be improved to 10,000 hours or more. Furthermore, the yield has increased.

Note that the height of the protrusion PB can also be reduced by reducing the off-angle θ _m ^<1-100> in the <1-100> direction of the nitride semiconductor substrate 11, other than by increasing the growth temperature of the n-type AlGaN first cladding layer 13 and the n-type AlGaN second cladding layer 15. Furthermore, by setting the absolute value of the off-angle θ ^<11-20> in the <11-20> direction of the nitride semiconductor substrate 11 to 0.4° or more, the flatness of the flat portion PH of the nitride semiconductor substrate 11 is improved, and the yield can be improved.

FIG. 6A is a graph showing the relationship between the thickness of the protrusion of the nitride semiconductor layer and the growth temperature (T _g ^n-clad ) of the n-type nitride cladding layer when the off-angle (θ _m ^<1-100> ) in the <1-100> direction of the nitride semiconductor substrate of FIG. 1 is changed.
In FIG. 6A , when the growth temperature T _g ^n-clad of the n-type AlGaN first cladding layer 13 and the n-type AlGaN second cladding layer 15 is 1050° C., the off angle θ _m ^<1-100> in the <1-100> direction of the nitride semiconductor substrate 11 is an off angle larger than 0.1. For example, when a nitride semiconductor substrate 11 having an off angle of 0.32° is used, the total layer thickness of the protruding portion PB is about 1.3 times thicker than the total layer thickness of the flat portion PH (protruding portion thickness/flat portion thickness=1.3). On the other hand, when a nitride semiconductor substrate 11 having an absolute value of the off angle θ _m ^<1-100> in the <1-100> direction of the nitride semiconductor substrate 11 of 0.1° or less is used, the protrusion thickness/flat portion thickness becomes 1.2 or less even when the growth temperature T _g ^n-clad of the n-type AlGaN first cladding layer 13 and the n-type AlGaN second cladding layer 15 remains at 1050° C.

FIG. 6B is a diagram showing the relationship between the off angle (deg) in the <1-100> direction of the nitride semiconductor substrate of FIG. 1 and the probability (%) of crack occurrence in the nitride semiconductor layer.
6B, the growth temperature T _g ^n-clad of the n-type AlGaN first cladding layer 13 and the n-type AlGaN second cladding layer 15 is set to 1050° C. Even in this case, it is found that the occurrence of cracks can be suppressed so long as the absolute value of the off-angle θ _m ^<1-100> in the <1-100> direction of the nitride semiconductor substrate 11 is 0.1° or less.

FIG. 6C is a diagram showing the relationship between the off angle in the <11-20> direction of the nitride semiconductor substrate of FIG. 1 and the yield.
6C, when the absolute value of the off-angle θ ^<11-20> of the nitride semiconductor substrate 11 in the <11-20> direction is smaller than 0.4°, the flatness of the wafer surface deteriorates, particularly when the substrate temperature is low. As a result, the fluctuation range of the divergence angle and kink level of the semiconductor laser LA increases, resulting in a decrease in yield.
On the other hand, when the absolute value of the off angle θ ^<11-20> in the <11-20> direction of the nitride semiconductor substrate 11 is 0.4° or more, even if the substrate temperature is low, the flatness of the wafer is maintained, the fluctuation range of the divergence angle and the kink level is stabilized, and the yield is improved.

As described above, by using a nitride semiconductor substrate 11 having a (0001) plane orientation, an absolute value of the off-angle in the <1-100> direction of 0.1 degrees or less, and an absolute value of the off-angle in the <11-20> direction of 0.4 degrees or more, it is possible to improve the flatness of the flat portion PH of the nitride semiconductor layer ML and suppress the increase in cracks even when the substrate temperature is low. In this case, it is not necessary to increase the substrate temperature, and as shown in FIG. 3(a), it is possible to prevent the disappearance of the depression KM recessed in the direction between the side surface KS and the bottom surface KB of the recess UB. Therefore, it is possible to make it difficult for dislocations and defects to reach the direction of the flat portion PH of the nitride semiconductor layer ML, and to improve the reliability of the semiconductor laser LA.

FIG. 7( a ) is a plan view showing the concentration positions of defects in the nitride semiconductor layer of the semiconductor light emitting element according to the second embodiment, and FIG. 7( b ) is a cross-sectional view showing the concentration positions of defects in the nitride semiconductor layer of the semiconductor light emitting element according to the second embodiment.
In the semiconductor laser LA of Fig. 1, a recess UB is disposed on only one side of the ridge RG. In contrast, in the semiconductor laser LB of Fig. 7(a), a recess UB is disposed on both sides of the ridge RG. Other points of the semiconductor laser LB can be configured in the same way as the semiconductor laser LA of Fig. 1.

Here, the nitride semiconductor layer ML has a defect region KC. The defect region KC has a higher density of defects KD than the flat portion PH of the nitride semiconductor layer ML. The defect region KC is provided between the recess UB and the flat portion PH of the nitride semiconductor layer ML. At this time, in the plane of the nitride semiconductor layer ML, the defects KD are concentrated in the vicinity of the side surface KS of the recess UB. In addition, in the film thickness direction of the nitride semiconductor layer ML, the defects KD are concentrated toward the interface between the InGaN underlayer 14 and the n-type AlGaN second cladding layer 15, as shown in FIG. 7(b). The InGaN underlayer 14 can relieve the distortion of the n-type AlGaN second cladding layer 15 caused by the lattice mismatch with the nitride semiconductor substrate 11.

Here, by providing the defect region KC in the nitride semiconductor layer ML, the formation of dislocations and defects in the flat portion PH of the nitride semiconductor layer ML can be suppressed, and the reliability of the semiconductor laser LB can be improved. In addition, by providing the InGaN underlayer 14 between the n-type AlGaN first cladding layer 13 and the n-type AlGaN second cladding layer 15, the strain in the stacking direction in the flat portion PH can be alleviated. This allows dislocations and defects to be concentrated in the vicinity of the recess UB, and the formation of dislocations and defects in the flat portion PH of the nitride semiconductor layer ML can be suppressed.

Figure 8 is a plan view showing the state of defects when the growth temperature of the nitride semiconductor layer of the semiconductor light emitting device according to the second embodiment is changed. Note that Figures 8(a) to 8(c) show the cases where the growth temperatures of the n-type AlGaN first cladding layer 13 and the n-type AlGaN second cladding layer 15 in Figure 2 are set to 1150°C, 1100°C, and 1050°C, respectively. That is, Figure 8(a) shows the state when the growth temperature is set to 1150°C, Figure 8(b) shows the state when the growth temperature is set to 1100°C, and Figure 8(c) shows the state when the growth temperature is set to 1050°C.

In Fig. 8(a) to Fig. 8(c), when the growth temperature T _g ^n-clad of the n-type AlGaN first cladding layer 13 and the n-type AlGaN second cladding layer 15 increases, the number of defects KD generated in the nitride semiconductor layer ML increases. Here, Fig. 8(a) shows a case where the dent KM is not formed in the direction between the side surface KS and the bottom surface KB of the recess UB, and the lateral thickness of the nitride semiconductor layer ML is inclined so as to become thicker from the side surface KS to the bottom surface KB of the recess UB, as shown in Fig. 3(a). In this case, as shown in Fig. 8(a), the defect KD generated in the protrusion portion PB on the side of the recess UB extends to the current injection region of the flat portion PH, and the defect KD reaches the light emitting layer during the operation of the semiconductor laser LA, which may cause rapid deterioration of the semiconductor laser LA.

Here, when the growth temperature T _g ^n-clad of the n-type AlGaN first cladding layer 13 and the n-type AlGaN second cladding layer 15 is lowered, as shown in FIG. 3(b) and FIG. 3(c), a depression KM is formed in the direction between the side surface KS and the bottom surface KB of the recess UB, and the depth of the depression KM becomes deeper as the growth temperature T _g ^n-clad becomes lower. As a result, the defects KD generated in the nitride semiconductor layer ML can be reduced. At this time, the defects KD generated in the protrusion portion PB on the side of the recess UB are locally concentrated on the protrusion portion PB on the side of the recess UB as shown in FIG. 8(b) and FIG. 8(c), and are hardly present in the current injection region of the flat portion PH. In addition, by concentrating the defects KD on the side of the recess UB, the stress of the entire laser element is relaxed, and the defects KD are less likely to multiply during the operation of the laser element, and the reliability of the semiconductor laser LA can be improved.

FIG. 9 is a cross-sectional view showing the configuration of the semiconductor light emitting device according to the third embodiment, taken in a direction perpendicular to the optical waveguide direction.
9, the semiconductor laser LC includes a nitride semiconductor layer ML' instead of the nitride semiconductor layer ML of the semiconductor laser LA of FIG. 1. The nitride semiconductor layer ML' includes a current injection layer 25 instead of the ridge RG of FIG. 1. The current injection layer 25 is located in the flat portion PH of the nitride semiconductor layer ML'. The current injection layer 25 can be configured with a stacked structure of the p-type AlGaN cladding layer 20 and the p-type GaN contact layer 21 of FIG. 2. The current injection layer 25 can be formed parallel to the recess UB across the end faces of the nitride semiconductor layer ML'. The current injection layer 25 includes a current confinement layer 26 that constricts the current injected into the active layer 17 of FIG. 2. The current confinement layer 26 can be, for example, a high resistance layer made of AlN. The current confinement layer 26 includes an opening 27 that allows current to be injected into the active layer 17 through the current injection layer 25. Other than that, the nitride semiconductor layer ML' can be configured similarly to the nitride semiconductor layer ML in Fig. 1. In this case, the semiconductor laser LC can be an inner stripe type laser.

An electrode 29 is formed on the nitride semiconductor layer ML' via an insulating layer 28. At this time, the top surface of the current injection layer 25 is exposed from the insulating layer 28 and is connected to the electrode 29.

Here, the thickness TP of the nitride semiconductor layer ML' at the position of the protrusion PB is set to be 1.0 to 1.2 times the thickness TH of the nitride semiconductor layer ML' at the position of the flat portion PH. With this configuration, even when the composition of the nitride semiconductor layer ML' is set so that the emission wavelength is in the near-ultraviolet region, it is possible to suppress the increase in cracks while suppressing the decrease in flatness of the flat portion PH of the nitride semiconductor layer ML'.
Furthermore, by providing the current confinement layer 26 in the current injection layer 25, it is possible to confine the guided light that propagates through the active layer 17 in the lateral direction, while confining the current injected into the active layer 17. As a result, it is possible to reduce the threshold current of the semiconductor laser LC, while suppressing heat generation from the semiconductor laser LC, and to increase the output of the semiconductor laser LC.

In addition, in this semiconductor laser LC, the defect region KC in FIG. 7 may be provided between the recess UB and the flat portion PH of the nitride semiconductor layer ML'.

FIG. 10 is a cross-sectional view showing the configuration of the semiconductor light emitting device according to the fourth embodiment, taken in a direction perpendicular to the optical waveguide direction.
The semiconductor laser LA in Fig. 1 includes side surfaces KS on both sides of the recess UB. In contrast to this, the semiconductor laser LD in Fig. 10 includes only one side surface KS of the recess UB. Other than that, the semiconductor laser LD can be configured similarly to the semiconductor laser LA in Fig. 1. Here, by configuring the semiconductor laser LD to include only one side surface KS of the recess UB, it is possible to miniaturize the semiconductor laser LD while leaving the defect region KC of the semiconductor laser LB in Fig. 7(a) on one side of the ridge RG.

FIG. 11 is a cross-sectional view showing the configuration of a semiconductor light emitting device according to the fifth embodiment, taken in a direction perpendicular to the optical waveguide direction.
In the semiconductor laser LD of Fig. 10, the recess UB including only one side KS is arranged on only one side of the ridge RG. In contrast, in the semiconductor laser LE of Fig. 11, the recess UB including only one side KS is arranged on both sides of the ridge RG. Other points of the semiconductor laser LE can be configured in the same way as the semiconductor laser LD of Fig. 10. Here, by arranging the recess UB including only one side KS on both sides of the ridge RG, the semiconductor laser LE can be cut out from the wafer while leaving the defect region KC of the semiconductor laser LB of Fig. 7(a) on both sides of the ridge RG. In this case, the recess UB becomes the dividing part of the laser element, and the defects formed in the part corresponding to the dividing width do not remain in the element, resulting in fewer defects overall.

Note that while Figures 10 and 11 show cases where the configurations are applied to the ridge stripe type laser of Figure 1, the configurations of Figures 10 and 11 may also be applied to the inner stripe type laser of Figure 9.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-mentioned embodiments and includes various modified examples. For example, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace part of the configuration of each embodiment with other configurations.

LA Semiconductor laser 11 Nitride semiconductor substrate ML Nitride semiconductor layer MH Flat surface UB Recess KB Flat portion PB Protrusion KM Recess RG Ridge 23 Insulating layers 22, 24 Electrodes

Claims (8)

a nitride semiconductor substrate having a recess formed on a flat surface;
a nitride semiconductor layer formed from the recess to the flat surface of the nitride semiconductor substrate and having a flat portion on the flat surface;
a protrusion formed in the nitride semiconductor layer on an end of the flat surface adjacent to the recess,
a thickness of the nitride semiconductor layer at the position of the protrusion is 1.0 to 1.2 times a thickness of the nitride semiconductor layer at the position of the flat portion,
a defect region having a higher density of crystal defects than the flat portion is provided between the recess and the flat portion;
The nitride semiconductor layer is
a cladding layer made of a nitride semiconductor having an Al composition of 8% or more;
an underlayer located within the cladding layer and made of a nitride semiconductor not containing Al;
The nitride semiconductor light-emitting device , wherein the defect region is located at an interface between the cladding layer and the underlayer . The nitride semiconductor light-emitting device according to claim 1, characterized in that the nitride semiconductor layer has a recess that is recessed in a direction between the side surface and the bottom surface of the recess. The nitride semiconductor light-emitting device according to claim 1, characterized in that the nitride semiconductor substrate has a (0001) plane orientation and an absolute value of the off-angle in the <1-100> direction is 0.1 degrees or less. The nitride semiconductor light-emitting device according to claim 1, characterized in that the absolute value of the off-angle in the <11-20> direction of the nitride semiconductor substrate is 0.4 degrees or more. The nitride semiconductor light-emitting device according to claim 1, characterized in that the nitride semiconductor layer has an inner stripe structure in which a current confinement layer is embedded in the nitride semiconductor layer. The nitride semiconductor light-emitting element according to claim 1, characterized in that the emission wavelength is 390 nm or less. 2. The nitride semiconductor light-emitting device according to claim 1, wherein the nitride semiconductor substrate has a (0001) plane orientation, an absolute value of an off-angle in a <1-100> direction being 0.1 degrees or less, and an absolute value of an off-angle in a <11-20> direction being 0.4 degrees or more. A step A of forming a recess on a flat surface of a nitride semiconductor substrate;
a step B of forming a nitride semiconductor layer having a flat portion on the flat surface of the nitride semiconductor substrate and a protrusion portion on an end portion of the flat surface adjacent to the recess from the recess to the flat surface of the nitride semiconductor substrate;
In the step B, a growth temperature of the nitride semiconductor layer is set so that a thickness of the nitride semiconductor layer at the position of the protrusion is 1.0 to 1.2 times a thickness of the nitride semiconductor layer at the position of the flat portion ,
In the step B, a defect region having a higher density of crystal defects than the flat portion is formed between the recess and the flat portion,
The nitride semiconductor layer is
a cladding layer made of a nitride semiconductor having an Al composition of 8% or more;
an underlayer located within the cladding layer and made of a nitride semiconductor not containing Al;
4. A method for manufacturing a nitride semiconductor light-emitting device, wherein the defect region is located at an interface between the cladding layer and the underlayer .

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