JP7340974B2 - Nitride semiconductor laser device - Google Patents

Description

The present disclosure relates to a nitride semiconductor laser device having a waveguide portion whose width is modulated with respect to the position in the cavity length direction.

In recent years, semiconductor laser elements have been used as light sources for image display devices such as displays and projectors, light sources for vehicle headlamps, light sources for industrial and consumer lighting, and industrial applications such as laser welding equipment, thin film annealing equipment, and laser processing equipment. It is attracting attention as a light source for a variety of uses, including as a light source for equipment. In addition, a semiconductor laser device used as a light source for the above applications is desired to have a high optical output of much more than 1 watt and high beam quality.

To achieve high beam quality, it is desirable that the laser oscillate in the fundamental mode (ie, the fundamental transverse mode). In order to achieve fundamental mode operation, there is a method of reducing the width of the waveguide and operating it in a state where higher-order modes optically do not exist (cutoff state). However, in order to achieve high output, it is advantageous to have a wide waveguide (wide stripe), so the transverse mode of high-power laser light with an optical output exceeding 1 watt is a high-order mode. There are many cases. Hereinafter, the higher-order mode in the lateral direction will also be simply referred to as a "higher-order mode."

Patent Document 1 discloses a conventional nitride semiconductor laser device. FIG. 12 is a top view showing the configuration of a conventional nitride semiconductor laser device 1000 disclosed in Patent Document 1.

As shown in FIG. 12, a conventional nitride semiconductor laser device 1000 has a rough surface optical waveguide mechanism 1001 provided at the center in the waveguide direction on both sides of a striped ridge portion, and a rough surface optical waveguide mechanism 1001 provided at both ends in the waveguide direction. A parallel smooth optical waveguide mechanism 1002 is provided. Since the rough optical waveguide mechanism 1001 causes loss in higher-order modes, the proportion of the fundamental mode can be increased.

Japanese Patent Application Publication No. 9-246664

However, in the nitride semiconductor laser device 1000 described in Patent Document 1, ripples (disturbances) may occur in the vertical FFP (Far-Field Pattern).

An object of the present disclosure is to provide a nitride semiconductor laser device that can suppress ripples in vertical FFP.

In order to achieve the above object, one embodiment of a nitride semiconductor laser device according to the present disclosure is a nitride semiconductor laser device that emits laser light, which includes a substrate and a first semiconductor disposed above the substrate. a light emitting layer disposed above the first semiconductor layer, a second semiconductor layer disposed above the light emitting layer, and a dielectric layer disposed above the second semiconductor layer. , the second semiconductor layer has a waveguide portion that guides the laser beam, and the width of at least a portion of the waveguide portion is at a position in the resonator length direction that is the longitudinal direction of the waveguide portion. The angle between the side surface that intersects the width direction of the waveguide section and the resonator length direction is defined by the effective refractive index of the inside of the waveguide section and the outside of the waveguide section. The nitride semiconductor laser device further includes a high refractive index portion having a refractive index higher than that of the dielectric layer, which is disposed in the recess formed on the side surface of the waveguide portion.

In this way, when the angle formed between the side surface of the waveguide section and the resonator length direction is large, the laser light passes through the waveguide in the narrow part of the waveguide section, that is, in the recess formed on the side surface of the waveguide section. propagate outside the section. In the nitride semiconductor laser device according to the present disclosure, since the high refractive index portion is provided in the recess formed on the side surface of the waveguide portion, laser light propagating outside the waveguide portion can be moved to the high refractive index portion. can. Therefore, it is possible to reduce the substrate mode caused by the laser light propagating outside the waveguide section moving toward the substrate, so that ripples in the vertical FFP caused by the substrate mode can be suppressed.

Further, in one aspect of the nitride semiconductor laser device according to the present disclosure, the limit angle may be a maximum value of an angle at which the laser beam is totally reflected at the side surface.

As a result, total reflection of the laser light incident on the side surface of the waveguide section is suppressed, so that the laser light propagates outside the waveguide section more reliably. Therefore, the effect of the high refractive index portion becomes even more remarkable.

Furthermore, in one aspect of the nitride semiconductor laser device according to the present disclosure, the high refractive index portion may be formed of a nitride semiconductor.

This allows the high refractive index portion to be formed in the same process as the second semiconductor layer, thereby simplifying the manufacturing process of the nitride semiconductor laser device.

Furthermore, in one aspect of the nitride semiconductor laser device according to the present disclosure, the high refractive index portion may be formed of a dielectric material.

Furthermore, in one aspect of the nitride semiconductor laser device according to the present disclosure, at least a portion of the high refractive index portion may be an ion implantation region into which ions are implanted.

As a result, light is absorbed in the ion implantation region placed outside the waveguide, increasing the loss of higher-order modes passing outside the waveguide, and reducing the fundamental mode (that is, the fundamental transverse mode). The ratio can be increased.

Further, in one aspect of the nitride semiconductor laser device according to the present disclosure, the substrate is disposed in a region located below the high refractive index portion of the main surface facing the first semiconductor layer, and has an uneven shape. It may have a scattering portion having a shape.

Such a scattering section can scatter high-order modes passing outside the waveguide section, so that high-order modes included in the laser light emitted from the front end face can be reduced. Therefore, it is possible to increase the ratio of the fundamental mode included in the laser light emitted from the front end face.

According to the present disclosure, it is possible to provide a nitride semiconductor laser device that can suppress ripples in vertical FFP.

FIG. 1A is a schematic top view showing the configuration of a nitride semiconductor laser device according to Embodiment 1. FIG. 1B is a schematic cross-sectional view showing the configuration of the nitride semiconductor laser device according to the first embodiment. FIG. 1C is a graph showing a calculation result of the relationship between the refractive index difference inside and outside the waveguide portion and the limit angle according to the first embodiment. FIG. 1D shows the calculation result of the relationship between the distance and the minimum value of the width of the waveguide section when the maximum value of the width of the waveguide section is fixed and the limit angle is changed as a parameter according to Embodiment 1. This is a graph showing. FIG. 2A is a schematic cross-sectional view showing the steps of forming the first semiconductor layer, the light emitting layer, and the second semiconductor layer in the method for manufacturing the nitride semiconductor laser device according to the first embodiment. FIG. 2B is a schematic cross-sectional view showing a step of forming a first protective film in the method for manufacturing a nitride semiconductor laser device according to the first embodiment. FIG. 2C is a schematic cross-sectional view showing a step of patterning the first protective film in the method for manufacturing a nitride semiconductor laser device according to the first embodiment. FIG. 2D is a schematic cross-sectional view showing a step of forming a waveguide portion, a flat portion, and a high refractive index portion in the method for manufacturing a nitride semiconductor laser device according to the first embodiment. FIG. 2E is a schematic cross-sectional view showing a step of forming a dielectric layer in the method for manufacturing a nitride semiconductor laser device according to the first embodiment. FIG. 2F is a schematic cross-sectional view showing a step of forming a p-side electrode in the method for manufacturing a nitride semiconductor laser device according to the first embodiment. FIG. 2G is a schematic cross-sectional view showing a step of forming a pad electrode in the method for manufacturing a nitride semiconductor laser device according to the first embodiment. FIG. 2H is a schematic cross-sectional view showing a step of forming an n-side electrode in the method for manufacturing a nitride semiconductor laser device according to the first embodiment. FIG. 3A is a schematic top view of a semiconductor laser device in which the nitride semiconductor laser element according to Embodiment 1 is mounted. FIG. 3B is a schematic cross-sectional view of a semiconductor laser device in which the nitride semiconductor laser element according to the first embodiment is mounted. FIG. 4A is a top view showing a simplified configuration of a nitride semiconductor laser device of Comparative Example 1. FIG. 4B is a first cross-sectional view showing the fundamental mode light distribution of laser light in the nitride semiconductor laser device of Comparative Example 1. FIG. 4C is a second cross-sectional view showing the fundamental mode light distribution of laser light in the nitride semiconductor laser device of Comparative Example 1. FIG. 4D is a top view showing a simplified configuration of a nitride semiconductor laser device of Comparative Example 2. FIG. 5 is a graph showing experimental results of vertical FFP when the structure of each waveguide section of the nitride semiconductor laser devices of Comparative Examples 1 and 2 was changed. FIG. 6A is a top view showing a simplified configuration of the nitride semiconductor laser device according to the first embodiment. FIG. 6B is a cross-sectional view showing the fundamental mode light distribution of laser light in the nitride semiconductor laser device according to the first embodiment. FIG. 7A is a schematic top view showing the configuration of a nitride semiconductor laser device according to the second embodiment. FIG. 7B is a schematic cross-sectional view showing the configuration of a nitride semiconductor laser device according to the second embodiment. FIG. 8A is a schematic diagram showing a step of laminating a first semiconductor layer, a light emitting layer, and a second semiconductor layer to form a waveguide portion and a flat portion in the method for manufacturing a nitride semiconductor laser device according to the second embodiment. FIG. FIG. 8B is a schematic cross-sectional view showing a step of forming a high refractive index portion and a second protective film in the method for manufacturing a nitride semiconductor laser device according to the second embodiment. FIG. 8C is a schematic cross-sectional view showing a step of patterning a high refractive index portion in the method for manufacturing a nitride semiconductor laser device according to the second embodiment. FIG. 8D is a schematic cross-sectional view showing a step of forming a dielectric layer and a p-side electrode in the method for manufacturing a nitride semiconductor laser device according to the second embodiment. FIG. 9A is a schematic top view showing the configuration of a nitride semiconductor laser device according to Embodiment 3. FIG. 9B is a schematic cross-sectional view showing the configuration of a nitride semiconductor laser device according to Embodiment 3. FIG. 10A is a schematic top view showing the configuration of a nitride semiconductor laser device according to Embodiment 4. FIG. 10B is a schematic cross-sectional view showing the configuration of a nitride semiconductor laser device according to Embodiment 4. FIG. 11 is a schematic top view showing the configuration of a nitride semiconductor laser device according to the fifth embodiment. FIG. 12 is a top view showing the configuration of a conventional nitride semiconductor laser device.

Embodiments of the present disclosure will be described below with reference to the drawings. Note that the embodiments described below each represent a specific example of the present disclosure. Therefore, the numerical values, shapes, materials, components, arrangement positions and connection forms of the components shown in the following embodiments are merely examples and do not limit the present disclosure.

Furthermore, each figure is a schematic diagram and is not necessarily strictly illustrated. Therefore, the scale etc. in each figure are not necessarily the same. In addition, in each figure, the same code|symbol is attached to the substantially the same structure, and the overlapping description is omitted or simplified.

Furthermore, in this specification, the terms "upper" and "lower" do not refer to the upper direction (vertically upward) or the lower direction (vertically downward) in absolute spatial recognition, but are based on the stacking order in the stacked structure. Used as a term defined by the relative positional relationship. Additionally, the terms "above" and "below" are used not only when two components are spaced apart and there is another component between them; This also applies when they are placed in contact with each other.

Furthermore, in this specification and the drawings, the X-axis, Y-axis, and Z-axis represent three axes of a three-dimensional orthogonal coordinate system. The X-axis and the Y-axis are orthogonal to each other, and both are orthogonal to the Z-axis.

(Embodiment 1)
A nitride semiconductor laser device according to Embodiment 1 will be described.

[Structure of nitride semiconductor laser device]
First, the configuration of the nitride semiconductor laser device according to this embodiment will be explained using FIG. 1A and FIG. 1B. 1A and 1B are a schematic top view and a cross-sectional view, respectively, showing the configuration of a nitride semiconductor laser device 1 according to the present embodiment. FIG. 1B shows a cross section of the nitride semiconductor laser device 1 taken along line IB-IB in FIG. 1A.

The nitride semiconductor laser device 1 according to this embodiment is a device that emits laser light and includes a nitride semiconductor. As shown in FIG. 1B, it includes a substrate 10, a first semiconductor layer 20, a light emitting layer 30, a second semiconductor layer 40, a dielectric layer 60, and a high refractive index section 44. In this embodiment, nitride semiconductor laser device 1 further includes an electrode member 50 and an n-side electrode 80. The nitride semiconductor laser device 1 has a resonator formed by a front end surface Cf and a rear end surface Cr, and emits laser light from the front end surface Cf.

The substrate 10 is, for example, a GaN substrate. In this embodiment, an n-type hexagonal GaN substrate whose main surface is a (0001) plane is used as the substrate 10. The thickness of the substrate 10 may be such that it can be cleaved when dividing the nitride semiconductor laser device 1 into individual pieces, and is, for example, 50 μm or more and 130 μm or less. In this embodiment, the thickness of the substrate 10 is 90 μm.

The first semiconductor layer 20 is a first conductivity type nitride semiconductor layer disposed above the substrate 10. In this embodiment, the first semiconductor layer 20 is an n-side cladding layer made of n-type Al _0.03 Ga _0.97 N and has a thickness of 3 μm. Note that the thickness and Al composition of the first semiconductor layer 20 are not limited to the above example. For example, the thickness of the first semiconductor layer 20 may be 0.5 μm or more and 5.0 μm or less, and the Al composition may be n-type Al _x Ga _1-x N (0<x<1). . Further, the first semiconductor layer 20 may include an n-type semiconductor layer other than n-type Al _0.03 Ga _0.97 N. Note that if at least one of the thickness and Al composition of the n-side cladding layer is too large, problems such as cracks occurring due to a difference in lattice constant with the GaN substrate and an increase in operating voltage due to an increase in series resistance may occur. obtain.

The light emitting layer 30 is a nitride semiconductor layer disposed above the first semiconductor layer 20. In this embodiment, the light emitting layer 30 includes an n-side light guide layer 31 made of n-type GaN with a thickness of 0.2 μm, an In _0.06 Ga _0.94 N quantum well layer with a thickness of 10 nm, and an In 0.06 Ga 0.94 N quantum well layer with a thickness of 5 nm. It has a laminated structure of an active layer 32 sandwiched between In _0.02 Ga _0.98 N barrier layers and a p-side optical guide layer 33 made of p-type GaN and having a thickness of 0.1 μm. In this embodiment, active layer 32 includes two quantum well layers, each of which is sandwiched between barrier layers. Note that the number of quantum well layers is not limited to two, and may be one or three or more. Further, the In composition and thickness of the quantum well layer and the barrier layer are not limited to these, but may be any composition and thickness that can emit light of about 400 nm or more and 470 nm or less.

The second semiconductor layer 40 is a second conductivity type nitride semiconductor layer disposed above the light emitting layer 30, and has a waveguide portion 40a that guides laser light. Here, the second conductivity type is a conductivity type different from the first conductivity type. In this embodiment, the second semiconductor layer 40 includes an electron barrier layer 41 made of Al _0.35 Ga _0.65 N with a thickness of 10 nm and a p-type Al _0.06 Ga _0.94 with a thickness of 1.5 nm. A p-side cladding layer 42 made of a strained superlattice with a thickness of 0.66 μm formed by repeating 220 cycles of N and p-type GaN with a thickness of 1.5 nm, and a p-side layer made of p-type GaN with a thickness of 0.05 μm. It has a laminated structure with a contact layer 43. The p-side contact layer 43 is formed as the top layer of the waveguide section 40a. Note that the configuration of the p-side cladding layer 42 is not limited to this. The thickness of the p-side cladding layer 42 may be, for example, 0.3 μm or more and 1 μm or less, and the composition may be p-type Al _x Ga _1-x N (0<x<1).

The p-side cladding layer 42 has a convex portion extending in the resonator length direction. The convex portion of the p-side cladding layer 42 and the p-side contact layer 43 constitute a striped (in other words, a ridge-like) waveguide portion 40a. Further, the p-side cladding layer 42 has flat portions as flat portions 40b on both sides of the waveguide portion 40a. That is, the uppermost surface of the flat portion 40b is the surface of the p-side cladding layer 42, and the p-side contact layer 43 is not formed on the uppermost surface of the flat portion 40b.

The height of the waveguide portion 40a (that is, the dimension in the Z-axis direction) is not particularly limited, but is, for example, 100 nm or more and 1 μm or less. In order to operate the nitride semiconductor laser device 1 at high optical output (for example, watt class), the height of the waveguide portion 40a may be set to 300 nm or more and 800 nm or less. In this embodiment, the height of the waveguide section 40a is 650 nm.

Further, as shown in FIG. 1A, the width of at least a portion of the waveguide section 40a is modulated with respect to the position in the resonator length direction (that is, the Y-axis direction in each figure), which is the longitudinal direction of the waveguide section 40a. has been done. Here, the width of the waveguide section 40a is the dimension of the waveguide section 40a in the direction perpendicular to the cavity length direction and the thickness direction of the second semiconductor layer 40 (that is, the Z-axis direction in each figure). . The detailed configuration of the waveguide section 40a will be described later.

The electrode member 50 is arranged above the second semiconductor layer 40. The electrode member 50 is wider than the waveguide section 40a. That is, the width of the electrode member 50 (that is, the width in the X-axis direction in each figure) is larger than the width of the waveguide section 40a (that is, the width in the X-axis direction in each figure). The electrode member 50 is in contact with the dielectric layer 60 and the upper surface of the waveguide section 40a.

In this embodiment, the electrode member 50 includes a p-side electrode 51 for supplying current and a pad electrode 52 arranged above the p-side electrode 51.

The p-side electrode 51 is in contact with the upper surface of the waveguide section 40a. The p-side electrode 51 is an ohmic electrode that makes ohmic contact with the p-side contact layer 43 above the waveguide section 40a, and is in contact with the top surface of the p-side contact layer 43, which is the top surface of the waveguide section 40a. The p-side electrode 51 is formed using, for example, a metal material such as Pd, Pt, or Ni. In this embodiment, the p-side electrode 51 has a two-layer structure of Pd/Pt.

The pad electrode 52 is wider than the waveguide section 40a and is in contact with the dielectric layer 60. That is, the pad electrode 52 is formed to cover the waveguide section 40a and the dielectric layer 60. The pad electrode 52 is formed using a metal material such as Ti, Ni, Pt, or Au, for example. In this embodiment, the pad electrode 52 has a three-layer structure of Ti/Pt/Au.

Note that, as shown in FIG. 1A, the pad electrode 52 is provided on the dielectric layer 60 in a top view of the nitride semiconductor laser device 1 in order to improve the yield when dividing the nitride semiconductor laser device 1 into pieces. It is formed inside (that is, inside the second semiconductor layer 40). That is, when nitride semiconductor laser device 1 is viewed from above, pad electrode 52 is not formed at the edge of the nitride semiconductor laser device 1 . In other words, the nitride semiconductor laser device 1 has a non-current injection region to which no current is supplied around the edge.

Dielectric layer 60 is arranged above second semiconductor layer 40 . The dielectric layer 60 is an insulating film having a lower refractive index than the waveguide portion 40a formed on the side surface of the waveguide portion 40a (that is, the surface intersecting the X-axis direction) in order to confine light in the waveguide portion 40a. be. Specifically, the dielectric layer 60 is continuously formed from the side surface of the waveguide section 40a to the flat section 40b. In this embodiment, the dielectric layer 60 is continuous around the waveguide portion 40a, extending over the side surface of the p-side contact layer 43, the side surface of the convex portion of the p-side cladding layer 42, and the top surface of the p-side cladding layer 42. It is formed by In this embodiment, dielectric layer 60 is formed of SiO ₂ .

Although the shape of the dielectric layer 60 is not particularly limited, the dielectric layer 60 may be in contact with the side surface of the waveguide section 40a and the flat section 40b. Thereby, light generated directly below the waveguide section 40a can be stably confined.

Further, in the nitride semiconductor laser device 1 intended to be operated with high optical output (that is, high-output operation), an end face coating film such as a dielectric multilayer film is formed on the front end face Cf. It is difficult to form this end face coating film only on the end face, and it also wraps around the upper face of the nitride semiconductor laser device 1. In this case, since the pad electrode 52 is not formed at the end of the nitride semiconductor laser device 1 in the cavity length direction (that is, the Y-axis direction in each figure), the end surface coating film wraps around to the top surface. In this case, the dielectric layer 60 and the end face coating film may come into contact with each other at the end of the nitride semiconductor laser device 1 in the cavity length direction. At this time, if the dielectric layer 60 is not formed or if the thickness of the dielectric layer 60 is thin for light confinement, the light will be affected by the end face coating film, which may cause optical loss. Become. Therefore, in order to sufficiently confine the light generated in the light emitting layer 30, the thickness of the dielectric layer 60 may be 100 nm or more. On the other hand, if the dielectric layer 60 is too thick, it becomes difficult to form the pad electrode 52, so the thickness of the dielectric layer 60 may be less than or equal to the height of the waveguide section 40a.

Further, on the side surfaces and flat portions 40b of the waveguide portion 40a, etching damage may remain during the etching process when forming the waveguide portion 40a and leakage current may occur. By covering 40b with dielectric layer 60, generation of unnecessary leakage current can be reduced.

The high refractive index section 44 is arranged in a recess 40d formed on the side surface of the waveguide section 40a, as shown in FIG. 1A. In other words, the high refractive index section 44 is arranged outside the narrowed portion of the waveguide section 40a in the width direction. The high refractive index portion 44 has a higher refractive index than the dielectric layer 60. In this embodiment, the high refractive index section 44 is formed of the same material as at least a portion of the second semiconductor layer 40. That is, the high refractive index section 44 is formed of a nitride semiconductor. The high refractive index section 44 is formed as a part of the second semiconductor layer 40. That is, the high refractive index section 44 is made up of the p-side cladding layer 42 and the p-side contact layer 43 similarly to the waveguide section 40a. The high refractive index section 44 is arranged in each of the plurality of recesses 40d formed on the side surface of the waveguide section 40a. The high refractive index section 44 has a triangular prism shape, and the width (that is, the dimension in the X-axis direction in each figure) varies depending on the position in the resonator length direction. At a position in the resonator length direction where the width of the waveguide section 40a becomes small, the width of the high refractive index section 44 becomes large.

The n-side electrode 80 is an electrode disposed below the substrate 10, and is an ohmic electrode that makes ohmic contact with the substrate 10. The n-side electrode 80 is, for example, a laminated film made of Ti/Pt/Au. The configuration of the n-side electrode 80 is not limited to this. The n-side electrode 80 may be a laminated film of Ti and Au.

[Detailed configuration of waveguide section and high refractive index section]
Next, detailed configurations of the waveguide section and the high refractive index section according to this embodiment will be explained.

As described above, the second semiconductor layer 40 includes a waveguide portion 40a consisting of a striped convex portion extending in the resonator length direction (that is, the Y-axis direction in each figure), and It has a flat portion 40b that extends in the direction (that is, the X-axis direction in each figure).

The width of at least a portion of the waveguide section 40a is modulated with respect to the position of the waveguide section 40a in the resonator length direction. In other words, the width of the waveguide section 40a varies with respect to the position in the resonator length direction. In this embodiment, the width of the waveguide portion 40a changes continuously, and wide portions and narrow portions are alternately arranged in the Y-axis direction. Here, as shown in FIG. 1A, the maximum value of the width of the waveguide portion 40a is assumed to be Wa, and the minimum value of the width is assumed to be Wb. In addition, the shortest distance in the Y-axis direction from the position where the width of the waveguide portion 40a is maximum to the position where the width is minimum, which is located on the front side (upper side of FIG. 1A), is defined as La, The shortest distance in the Y-axis direction from the position where the width of the waveguide portion 40a is maximum to the position where the width is minimum, which is located on the rear side (lower side in FIG. 1A), is defined as Lb. Further, in this embodiment, the width of the waveguide portion 40a changes linearly. Among the side surfaces of the waveguide section 40a, the angles formed by the side surfaces located on the front side and rear side of the position where the width of the waveguide section 40a is maximum and the resonator length direction are respectively defined as θa and θb, as follows. The relationship holds true.

θa=arctan {(Wa-Wb)/(2×La)}...(Formula 1)
θb=arctan {(Wa-Wb)/(2×Lb)}...(Formula 2)

The values of θa and θb become larger than a limit angle (defined as θc), which will be described later. That is, Wa, Wb, La, and Lb are set so as to satisfy the following relationship.

θa>θc and θb>θc (Formula 3)

In other words, the angle between the side surface of the waveguide section 40a in the width direction (that is, the X-axis direction) and the resonator length direction is defined by the effective refractive index of the inside of the waveguide section 40a and the outside of the waveguide section 40a. is larger than the limit angle θc. In this embodiment, the limit angle θc is the maximum value of the angle at which the laser beam is totally reflected on the side surface of the waveguide portion 40a.

As an example, the width of the waveguide portion 40a is 1 μm or more and 100 μm or less. In order to operate the nitride semiconductor laser device 1 at a high optical output (for example, watt class), the maximum value Wa of the width of the waveguide portion 40a may be set to 10 μm or more and 50 μm or less. The smaller the minimum value Wb of the width of the waveguide section 40a, the higher the mode component can be reduced, but if it becomes too small, the fundamental mode component (that is, the fundamental transverse mode component) will also be reduced due to loss. On the other hand, when the minimum value Wb of the width of the waveguide portion 40a is increased, the effect of reducing higher-order mode components becomes smaller. In order to efficiently suppress higher-order mode components while maintaining the intensity of the fundamental mode, the minimum width Wb of the waveguide section 40a is set to approximately 1/4 or more and 3/4 or less of the maximum width Wa. Good too.

Furthermore, if the distances La and Lb are made too small, θa and θb become large, so that (Equation 3) is no longer satisfied. On the other hand, if the distances La and Lb are made too large, the number of narrowed portions in the waveguide portion 40a will be reduced, and the effect of suppressing higher-order modes will be reduced. In this embodiment, Wa=16 μm, Wb=10 μm, and La=Lb=30 μm. At this time, θa=θb=5.7°.

Further, as long as the conditions of (Formula 1) and (Formula 2) are satisfied, La≠Lb may be satisfied. When La≠Lb, the loss to higher-order modes can be made different between the outgoing path and the returning path while the light reciprocates in the Y-axis direction within the resonator. For example, when La>Lb, the loss to higher-order modes when light travels from the rear side to the front side can be increased. Furthermore, since the proportion of the portion where the width becomes narrower from the rear side to the front side within the resonator (that is, the portion of the distance La in FIG. 1A) increases, the loss to higher-order modes further increases.

Further, as described above, in the recessed portion 40d on the side surface of the waveguide portion 40a (that is, outside the portion where the width of the waveguide portion 40a is narrowed), a high refractive index layer consisting of the p-side cladding layer 42 and the p-side contact layer 43 is provided. A section 44 is arranged. The high refractive index part 44 is formed outside the part where the waveguide part 40a is narrow (that is, the part near the position where the width is the minimum value Wb), and is formed outside the part where the width is wide (that is, the part where the width is the maximum value Wa). It is not formed outside of the position In this embodiment, the waveguide section 40a and the high refractive index section 44 are separated by a certain distance dd in the width direction of the waveguide section 40a (that is, the X-axis direction in each figure). In order for the high refractive index section 44 to have an effect on the light propagating outside the waveguide section 40a, it is necessary to satisfy the following (Formula 4).

Wb+2×dd<Wa・・・・・・・・・・・・・・・・(Formula 4)

Here, if the distance dd is too small, a large proportion of the fundamental mode component will be guided to the high refractive index section 44 and will spread to the outside of the waveguide section 40a. Along with this, the fundamental mode loss increases, so the distance dd needs to be increased to some extent. As a result of the inventor's studies, the loss of the fundamental mode component can be suppressed when the distance dd is 1 μm or more. Furthermore, the position of the end of the high refractive index section 44 on the opposite side to the waveguide section 40a in the width direction (that is, the X-axis direction in each figure) is the width of the portion where the width of the waveguide section 40a is the maximum value Wa. It may be at the same position as the end of the direction, or it may be outside. In this embodiment, dd=2 μm, and the position in the width direction of the end of the high refractive index portion 44 on the opposite side to the waveguide portion 40a is the width direction of the portion where the width of the waveguide portion 40a has the maximum value Wa. It is the same as the position of the end of .

Further, a dielectric layer 60 is formed on the p-side contact layer 43 of the high refractive index portion 44, and no current is injected from this portion. In this embodiment, the high refractive index portion 44 is covered with the dielectric layer 60, but if the pad electrode 52 is made of a material such as Au that makes a Schottky connection with the p-side contact layer 43, The pad electrode 52 may be formed directly on the p-side contact layer 43.

Next, a method for determining the limit angle θc will be explained. In this embodiment, calculations were performed using the equivalent refractive index method by approximating the three-dimensional structure of the waveguide section 40a (that is, the ridge structure) with a two-dimensional slab waveguide structure. First, the light distribution and equivalent refractive index (that is, effective refractive index) in the stacking direction are calculated using the thickness and refractive index of each layer along the Z1-Z1 line in FIG. 1B. Although details are omitted, the equivalent refractive index was calculated by discretizing the two-dimensional scalar wave equation and solving the eigenvalue problem. Defining the equivalent refractive index along the Z1-Z1 line in FIG. 1B as ni, in this embodiment, ni=2.535 was obtained. Similarly, when the equivalent refractive index along the Z2-Z2 line in FIG. 1B was defined as no, no=2.527 was obtained. These values depend on the thickness and refractive index of each semiconductor layer, but in the case of a waveguide structure having a convex portion as in this embodiment, the relationship ni>no is always satisfied.

Next, the maximum value of the angle (this angle is defined as the limit angle θc) when the total reflection condition is satisfied is calculated using Snell's law. According to Snell's law, the limit angle θc is expressed by the following formula.

θc=90-arcsin(no/ni)

In this embodiment, θc=4.6° is obtained, and the relationship of (Formula 3) is satisfied.

Note that since the limit angle θc depends on the thickness of each layer, the refractive index, and the height of the waveguide section 40a, calculation is required for each structure in structures other than this embodiment. Here, the relationship between the refractive index difference between the inside and outside of the waveguide section 40a and the limit angle θc will be explained using FIG. 1C. FIG. 1C is a graph showing the calculation result of the relationship between the refractive index difference (ni-no) between the inside and outside of the waveguide portion 40a and the limit angle θc according to the present embodiment. Here, the calculation was performed using ni=2.535. It can be seen that the larger the difference in refractive index between the inside of the waveguide section 40a and the outside of the waveguide section 40a, the larger the limit angle θc becomes.

Next, an example of the shape of the waveguide section 40a to realize the predetermined limit angle θc will be described using FIG. 1D. FIG. 1D shows the distance La and the minimum value Wb of the width of the waveguide portion 40a when the maximum value Wa of the width of the waveguide portion 40a according to the present embodiment is fixed and the limit angle θc is varied as a parameter. It is a graph showing the calculation result of the relationship. FIG. 1D shows the distance La that satisfies (Formula 3) and the minimum value Wb of the width of the waveguide portion 40a at their respective limit angles θc, when the maximum value Wa of the width of the waveguide portion 40a is 16 μm. The calculated results are shown. The condition of (Formula 3) is satisfied in the region below each straight line in FIG. 1D. The distance Lb can also be calculated in the same way.

In this embodiment, the width of the waveguide portion 40a is changed linearly, but it may be changed curved if the condition of (Equation 3) is satisfied. Furthermore, there may be a region in which the width does not change in a part of the waveguide section 40a.

[Method for manufacturing nitride semiconductor laser device]
Next, a method for manufacturing the nitride semiconductor laser device 1 according to this embodiment will be explained using FIGS. 2A to 2H. 2A to 2H are schematic cross-sectional views showing each step in the method for manufacturing nitride semiconductor laser device 1 according to the present embodiment.

First, as shown in FIG. 2A, on a substrate 10 which is an n-type hexagonal GaN substrate whose main surface is a (0001) plane, using a metalorganic chemical vapor deposition (MOCVD) method, The first semiconductor layer 20, the light emitting layer 30, and the second semiconductor layer 40 are sequentially formed.

Specifically, an n-side cladding layer made of n-type AlGaN is grown to a thickness of 3 μm as the first semiconductor layer 20 on a substrate 10 having a thickness of 400 μm. Subsequently, an n-side optical guide layer 31 made of n-type GaN is grown to a thickness of 0.2 μm. Subsequently, an active layer 32 consisting of two periods of a barrier layer made of InGaN and an InGaN quantum well layer is grown. Subsequently, a p-side optical guide layer 33 made of p-type GaN is grown to a thickness of 0.1 μm. Subsequently, an electron barrier layer 41 made of AlGaN is grown to a thickness of 10 nm. Subsequently, a p-side cladding layer 42 made of a strained superlattice with a thickness of 0.66 μm formed by repeating 220 cycles of a p-type AlGaN layer with a thickness of 1.5 nm and a GaN layer with a thickness of 1.5 nm is grown. Subsequently, a p-side contact layer 43 made of p-type GaN is grown to a thickness of 0.05 μm. Here, in each layer, trimethylgallium (TMG), trimethylammonium (TMA), and trimethylindium (TMI) are used as organic metal raw materials containing Ga, Al, and In, respectively. Furthermore, ammonia (NH ₃ ) is used as the nitrogen raw material.

Next, as shown in FIG. 2B, a first protective film 91 is formed on the second semiconductor layer 40. Specifically, a 300 nm silicon oxide film (SiO ₂ ) is formed as the first protective film 91 on the p-side contact layer 43 by a plasma CVD (Chemical Vapor Deposition) method using silane (SiH ₄ ). do. Note that the method for forming the first protective film 91 is not limited to the plasma CVD method, and may be a known film forming method such as a thermal CVD method, a sputtering method, a vacuum evaporation method, or a pulsed laser film forming method. Can be used. Furthermore, the material for forming the first protective film 91 is not limited to those mentioned above, and may be any material that is selective to the etching of the first semiconductor layer 20, which will be described later, such as a dielectric or a metal. Bye.

Next, as shown in FIG. 2C, the first protective film 91 is selectively removed using a photolithography method and an etching method so that the first protective film 91 remains in a predetermined shape. The predetermined shape is the shape of the waveguide section 40a and the high refractive index section 44 shown in FIG. 1A when viewed from above. The first protective film 91 having a predetermined shape includes a portion corresponding to the waveguide portion 40a and a portion corresponding to the high refractive index portion 44. The portion corresponding to the waveguide portion 40a is a band-shaped portion whose width is modulated with respect to the position in the resonator length direction, and the portion corresponding to the high refractive index portion 44 is arranged in the recess 40d of the band-shaped portion. It is an island-like part.

As the lithography method, a photolithography method using a short wavelength light source, an electron beam lithography method in which direct drawing is performed with an electron beam, a nanoimprint method, etc. can be used. Etching methods include, for example, dry etching using reactive ion etching (RIE) using a fluorine-based gas such as _CF4 , or wet etching using hydrofluoric acid (HF) diluted to about 1:10. can be used.

Next, as shown in FIG. 2D, by etching the p-side contact layer 43 and the p-side cladding layer 42 using the first protective film 91 formed in a predetermined shape as a mask, a waveguide is formed in the second semiconductor layer 40. A portion 40a, a flat portion 40b, and a high refractive index portion 44 are formed. Specifically, the waveguide section 40a is formed below the first protective film 91 located at the center in the horizontal direction shown in FIG. 2D, and is located to the side of the first protective film 91 (that is, in the A high refractive index portion 44 is formed below the first protective film 91. Further, the p-side contact layer 43 and the p-side cladding layer 42 in the region where the first protective film 91 is not formed are etched, thereby forming a flat portion 40b. As for etching the p-side contact layer 43 and the p-side cladding layer 42, dry etching by RIE using a chlorine-based gas such as Cl ₂ may be used.

Next, as shown in FIG. 2E, after removing the first protective film 91 having a predetermined shape by wet etching using hydrofluoric acid or the like, A dielectric layer 60 is deposited. That is, the dielectric layer 60 is formed on the waveguide section 40a, the flat section 40b, and the high refractive index section 44. As the dielectric layer 60, a silicon oxide film (SiO ₂ ) is formed to a thickness of 300 nm by, for example, a plasma CVD method using silane (SiH ₄ ).

Next, as shown in FIG. 2F, only the dielectric layer 60 on the waveguide section 40a is removed by photolithography and wet etching using hydrofluoric acid, and the upper surface of the p-side contact layer 43 is removed. expose. Thereafter, a p-side electrode 51 made of Pd/Pt is formed only on the waveguide portion 40a using a vacuum evaporation method and a lift-off method. Specifically, the p-side electrode 51 is formed on the p-side contact layer 43 exposed from the dielectric layer 60. Note that the method for forming the p-side electrode 51 is not limited to the vacuum evaporation method, and may be a sputtering method, a pulse laser film-forming method, or the like. Further, the electrode material of the p-side electrode 51 may be any material that makes ohmic contact with the second semiconductor layer 40 (p-side contact layer 43), such as Ni/Au-based or Pt-based material.

Next, as shown in FIG. 2G, a pad electrode 52 is formed to cover the p-side electrode 51 and the dielectric layer 60. Specifically, a negative resist is patterned using a photolithography method or the like in areas other than the desired area, and a pad electrode 52 made of Ti/Pt/Au is formed on the entire surface above the substrate 10 by a vacuum evaporation method or the like, and then lift-off is performed. Remove unnecessary portions of the electrode using a method. Thereby, the pad electrode 52 having a predetermined shape can be formed on the p-side electrode 51 and the dielectric layer 60. As described above, the electrode member 50 consisting of the p-side electrode 51 and the pad electrode 52 is formed.

Next, as shown in FIG. 2H, an n-side electrode 80 is formed on the lower surface of the substrate 10 (that is, the main surface on the back side of the main surface on which the first semiconductor layer 20 and the like are arranged). Specifically, the n-side electrode 80 made of Ti/Pt/Au is formed on the lower surface of the substrate 10 by vacuum evaporation or the like, and patterned using photolithography and etching to form the n-side electrode in a predetermined shape. form 80.

As described above, the nitride semiconductor laser device 1 according to this embodiment can be manufactured. In this embodiment, the high refractive index section 44 is formed of a nitride semiconductor as described above. Thereby, the high refractive index portion 44 can be formed in the same process as the second semiconductor layer 40, so the manufacturing process of the nitride semiconductor laser device 1 can be simplified.

[Packaging form of nitride semiconductor laser device]
Next, a mounting form of the nitride semiconductor laser device 1 according to the first embodiment will be described using FIGS. 3A and 3B. 3A and 3B are a schematic top view and a cross-sectional view, respectively, of a semiconductor laser device 2 in which a nitride semiconductor laser device 1 according to the present embodiment is mounted. FIG. 3B shows a cross section of the semiconductor laser device 2 taken along line IIIB-IIIB in FIG. 3A.

The semiconductor laser device 2 according to this embodiment includes a nitride semiconductor laser element 1 and a submount 100, as shown in FIG. 3B.

As shown in FIG. 3B, the submount 100 includes a base 101, a first electrode 102a, a second electrode 102b, a first adhesive layer 103a, and a second adhesive layer 103b.

The base 101 is a base disposed below the substrate 10 of the nitride semiconductor laser device 1, and functions as a heat sink. The material of the base 101 is not particularly limited, but may include ceramics such as aluminum nitride (AlN) and silicon carbide (SiC), diamond (C) deposited by CVD, metals such as Cu, and Al. It may be made of a single material or a material having a thermal conductivity equal to or higher than that of the nitride semiconductor laser element 1, such as an alloy such as CuW.

The first electrode 102a is arranged on one surface of the base 101, as shown in FIGS. 3A and 3B. Further, the second electrode 102b is arranged on the other surface of the base 101. The first electrode 102a and the second electrode 102b are, for example, a laminated film made of three metal films: Ti with a thickness of 0.1 μm, Pt with a thickness of 0.2 μm, and Au with a thickness of 0.2 μm.

The first adhesive layer 103a is arranged on the first electrode 102a. The second adhesive layer 103b is arranged on the second electrode 102b. The first adhesive layer 103a and the second adhesive layer 103b are, for example, eutectic solder made of a gold-tin alloy containing Au and Sn at a content of 70% and 30%, respectively.

Nitride semiconductor laser device 1 is mounted on submount 100 . In this embodiment, since the p-side (that is, the electrode member 50 side) of the nitride semiconductor laser device 1 is connected to the submount 100, that is, the junction-down mounting, the pad of the nitride semiconductor laser device 1 is Electrode 52 is connected to first adhesive layer 103a of submount 100.

Note that when mounting is performed using gold-tin solder on the first adhesive layer 103a as in this embodiment, the gold-tin solder causes a eutectic reaction with the gold of the pad electrode 52 and the gold of the first electrode 102a. Boundaries may be difficult to determine. In that case, the thickness of the first adhesive layer 103a ranges from a layer that does not react eutectically with the gold-tin solder of the pad electrode 52 (for example, Pt) to a layer that does not react eutectically with the gold-tin solder of the first electrode 102a (for example, Pt). , Pt).

Further, a wire 110 is connected to each of the pad electrode 52 of the nitride semiconductor laser device 1 and the first electrode 102a of the submount 100 by wire bonding. Thereby, current can be supplied to the nitride semiconductor laser device 1 through the wire 110.

Although not shown, the submount 100 is mounted on a metal package, such as a CAN package, for the purpose of improving heat dissipation and simplifying handling. That is, the submount 100 is bonded to the metal package by the second adhesive layer 103b. Note that the base 101 itself may function as a package. In this case, the submount 100 does not need to include the second adhesive layer 103b.

[Effects of nitride semiconductor laser device]
Next, the effects of the nitride semiconductor laser device 1 according to the present embodiment will be explained while comparing with a comparative example. First, the operation of the nitride semiconductor laser device of the comparative example will be explained using FIGS. 4A to 5. FIG. 4A is a top view showing a simplified configuration of a nitride semiconductor laser device of Comparative Example 1. Note that FIG. 4A also shows a schematic diagram of an example of the optical distribution of the fundamental mode and the optical distribution of higher-order modes of the laser beam of the nitride semiconductor laser device of Comparative Example 1. 4B and 4C are cross-sectional views showing fundamental mode light distributions DL1 and DL2 of laser light in the nitride semiconductor laser device of Comparative Example 1. 4B and 4C respectively show cross sections along the IVB-IVB line and IVC-IVC line in FIG. 4A, and the fundamental mode light distributions DL1 and DL2 in the cross sections. FIG. 4D is a top view showing a simplified configuration of a nitride semiconductor laser device of Comparative Example 2.

The nitride semiconductor laser device of Comparative Example 1 shown in FIG. 4A differs from the nitride semiconductor laser device 1 according to Embodiment 1 in that it does not include a high refractive index portion, and is the same in other respects. In the nitride semiconductor laser device of Comparative Example 1, laser light propagates in the Y-axis direction in the waveguide portion 40a during laser oscillation. At this time, even if there is a narrow portion of the waveguide portion 40a, the light propagates generally in the Y-axis direction. That is, FIG. 4A is a schematic diagram when the total reflection condition is not satisfied inside and outside the waveguide section 40a (that is, θa>θc, θb>θc). In FIG. 4A, the state of light propagation is shown by broken line arrows. In the part where the width of the waveguide section 40a becomes narrow, the light travels slightly inward due to the difference in refractive index between the inside and outside of the ridge, but since the condition for total reflection is not satisfied, most of the light travels outside the waveguide section 40a. It moves in the Y-axis direction.

As shown in fundamental mode light distribution DL1 in FIG. 4B, the light propagating within the waveguide section 40a is designed to be confined near the active layer 32. That is, the design is such that the light propagating within the waveguide section 40a does not impinge on the substrate 10. However, as shown in the fundamental mode light distribution DL2 in FIG. 4C, the light propagating outside the waveguide section 40a is directed toward the substrate 10 side because the thickness of the p-side cladding layer 42 outside the waveguide section 40a is thin. and is pushed down. Then, a vertical higher-order mode called a substrate mode is excited between the active layer 32 and the first semiconductor layer 20 (n-side cladding layer) and between the first semiconductor layer 20 and the substrate 10. When this substrate mode occurs, ripples occur in the vertical FFP. Such ripples are particularly increased by higher-order modes that have their optical intensity peaks outside the waveguide section 40a.

The nitride semiconductor laser device of Comparative Example 2 shown in FIG. 4D includes a waveguide portion 1040a. The nitride semiconductor laser device of Comparative Example 2 is different from the present invention in that it does not include a high refractive index portion and satisfies the conditions for total reflection inside and outside the waveguide portion 1040a (that is, satisfies θa<θc, θb<θc). It is different from the nitride semiconductor laser device 1 according to the embodiment, but is the same in other respects. In the nitride semiconductor laser device of Comparative Example 2, the difference in refractive index between the inside and outside of the waveguide portion 1040a satisfies the total reflection condition, so the light is reflected in the width direction of the waveguide portion 1040a, as indicated by the broken line arrow in FIG. 4D. It is reflected at the end and radiated out of the waveguide section 1040a. That is, since the light emitted to the outside as a laser beam does not propagate outside the waveguide section 1040a, the substrate mode that occurs in Comparative Example 1 shown in FIG. 4A is suppressed in the structure of the waveguide section 1040a of Comparative Example 2. . Therefore, according to the nitride semiconductor laser device of Comparative Example 2, ripples in the vertical FFP can be suppressed.

FIG. 5 is a graph showing experimental results of vertical FFP when the structure of each waveguide section of the nitride semiconductor laser devices of Comparative Examples 1 and 2 was changed. In this experiment, La=Lb and Wa=16 μm were fixed, and the distance La was varied at 15 μm intervals in the range from 15 μm to 90 μm. Further, the minimum width Wb was varied in a range of 4 μm to 10 μm at intervals of 2 μm. FIG. 5 shows the vertical FFP when the optical output is 1 W in a nitride semiconductor laser device having each of these structures. The vertical axis of each graph in FIG. 5 is normalized by the maximum value. Moreover, the horizontal axis indicates the standardized angle. In addition, in FIG. 5, there is a graph showing the vertical FFP from a nitride semiconductor laser device having a structure that satisfies the relationship (Formula 3), and a graph showing the vertical FFP from a nitride semiconductor laser device having a structure that does not satisfy the relationship (Formula 3). The boundary with the graph showing vertical FFP is indicated by a dashed line. The graph to the left of the dashed-dotted line shows the vertical FFP of the nitride semiconductor laser device that satisfies the relationship (Equation 3). As shown in the graph to the left of the dashed-dotted line in FIG. 5, it can be seen that ripples occur in the vertical FFP in the nitride semiconductor laser device having the structure of θa>θc and θb>θc. On the other hand, as shown in the graph on the right side of the dashed-dotted line in FIG. 5, it can be seen that no ripple occurs in the vertical FFP in the nitride semiconductor laser device having the structure where θa<θc and θb<θc. It can also be seen that the smaller the minimum width value Wb, the greater the ripple intensity. This is because the smaller the minimum width value Wb, the greater the proportion of light that passes outside the waveguide section 40a. Furthermore, it can be seen that in a structure where ripples occur, the closer the structure is to satisfying the relationships θa<θc and θb<θc, the smaller the ripples become. This is because the proportion of light that satisfies the total reflection conditions satisfying the relationships θa<θc and θb<θc increases.

As described above, in the nitride semiconductor laser device that satisfies the relationship (Equation 3), ripples occur in the vertical FFP. The nitride semiconductor laser device 1 according to the present embodiment includes a high refractive index portion 44 in order to satisfy the relationship of (Formula 3) and suppress ripples in the vertical FFP. The effects of the high refractive index portion 44 of the nitride semiconductor laser device 1 according to this embodiment will be described below with reference to FIGS. 6A and 6B. FIG. 6A is a top view showing a simplified configuration of nitride semiconductor laser device 1 according to this embodiment. FIG. 6B is a cross-sectional view showing the fundamental mode light distribution DL3 of laser light in the nitride semiconductor laser device 1 according to the present embodiment. FIG. 6B shows a cross section along the line VIB-VIB in FIG. 6A and a fundamental mode light distribution DL3 in the cross section.

As described above, the structure of the waveguide section 40a according to the present embodiment is set so as not to satisfy the total reflection condition (that is, to satisfy θa>θc, θb>θc). In FIG. 6A, the state of light propagation is shown by broken line arrows. In the part where the width of the waveguide section 40a becomes narrow, the light propagates slightly inward due to the difference in refractive index between the inside and outside of the waveguide section 40a, but since the condition for total reflection is not satisfied, most of the light passes through the waveguide section. 40a and proceeds in the Y-axis direction. A high refractive index section 44 is formed outside the waveguide section 40a, and light passing outside the waveguide section 40a passes directly under this high refractive index section 44. The high refractive index section 44 is formed of a p-side cladding layer 42 and a p-side contact layer 43, and these layers have a higher refractive index than the dielectric layer 60. When a layer with a high refractive index is formed above the light passage region (that is, on the second semiconductor layer 40 side with respect to the light emitting layer 30), light moves upward. In other words, the light that propagates outside the waveguide section 40a and reaches directly below the high refractive index section 44 moves upward. Therefore, as shown in FIG. 6B, the fundamental mode light distribution DL3 of the laser light according to the present embodiment is higher than the fundamental mode light distribution DL2 of the laser light when the high refractive index section 44 is not provided. Located in This makes it possible to reduce the amount of light that moves to the substrate 10 located below the light emitting layer 30, thereby reducing the substrate mode as shown in FIG. 4C. That is, according to the nitride semiconductor laser device 1 according to the present embodiment, ripples in the vertical FFP can be suppressed.

(Embodiment 2)
A nitride semiconductor laser device according to a second embodiment will be described. The nitride semiconductor laser device according to the present embodiment differs from the nitride semiconductor laser device 1 according to the first embodiment in that the high refractive index portion is formed of a dielectric material. The nitride semiconductor laser device according to the present embodiment will be described below, focusing on the differences from the nitride semiconductor laser device 1 according to the first embodiment.

[Structure of nitride semiconductor laser device]
First, the configuration of the nitride semiconductor laser device according to this embodiment will be described using FIGS. 7A and 7B. 7A and 7B are a schematic top view and a cross-sectional view, respectively, showing the configuration of a nitride semiconductor laser device 1a according to this embodiment. FIG. 7B shows a cross section of the nitride semiconductor laser device 1a taken along line VIIB-VIIB in FIG. 7A. As shown in FIG. 7B, the nitride semiconductor laser device 1a according to this embodiment includes a substrate 10, a first semiconductor layer 20, a light emitting layer 30, a second semiconductor layer 40, an electrode member 50, and a dielectric It includes a body layer 60, a high refractive index section 61, and an n-side electrode 80. The second semiconductor layer 40 has a waveguide section 40a and a flat section 40b.

The high refractive index portion 61 according to this embodiment is formed of a dielectric material having a higher refractive index than the dielectric layer 60. Similar to the high refractive index section 44 according to the first embodiment, the high refractive index section 61 includes a concave section 40d formed on the side surface of the waveguide section 40a (that is, a concave section 40d on the outside of the part where the width of the waveguide section 40a is narrowed). area). The upper and side surfaces of the high refractive index section 61 are covered with a dielectric layer 60. Since the high refractive index portion 61 has a higher refractive index than the dielectric layer 60, similarly to the first embodiment, light passing directly under the high refractive index portion 61 moves upward. Thereby, the occurrence of substrate mode can be suppressed. In other words, ripples in vertical FFP can be suppressed. Although the thickness of the high refractive index section 61 is not particularly limited, in this embodiment, the thickness of the high refractive index section 61 is 300 nm.

If a material with a higher refractive index than the dielectric layer 60 is used as the material of the high refractive index portion, the above effect will be produced. In this embodiment, dielectric layer 60 is made of SiO ₂ with a refractive index of 1.47. Therefore, as the material of the high refractive index portion 61, for example, SiN (refractive index: 2.07), Al ₂ O ₃ (refractive index: 1.79), AlN (refractive index: 2.19), ITO (refractive index ratio: 2.12), etc. can be used. ITO is sometimes used as an electrode material, but since it also has a light absorption effect, higher-order modes can be suppressed. That is, since the high-order mode having a high light intensity near the high-refractive-index portion 61 can be absorbed in the high-refractive-index portion 61 formed of ITO, the higher-order mode can be further suppressed.

[Method for manufacturing nitride semiconductor laser device]
Next, a method for manufacturing the nitride semiconductor laser device 1a according to this embodiment will be explained using FIGS. 8A to 8D. 8A to 8D are schematic cross-sectional views showing each step in the method for manufacturing the nitride semiconductor laser device 1a according to this embodiment. In the following, portions of the method for manufacturing the nitride semiconductor laser device 1a according to the present embodiment that are different from the method for manufacturing the nitride semiconductor laser device 1 according to the first embodiment will be explained.

First, as shown in FIG. 8A, the first semiconductor layer 20, the light emitting layer 30, and the second semiconductor layer are sequentially formed on the substrate 10, as in the steps of the first embodiment described using FIGS. 2A to 2D. The layers 40 are stacked to form a waveguide section 40a and a flat section 40b. Note that FIG. 8A is a cross-sectional view after removing the first protective film 91.

Next, as shown in FIG. 8B, a high refractive index portion 61 is formed on the entire upper surface of the second semiconductor layer 40, a second protective film 92 is formed above the high refractive index portion 61, and a photolithography method is applied. The second protective film 92 is patterned into a desired shape using an etching method. Specifically, the second protective film 92 is formed in the region where the high refractive index portion 61 is to be left in a later step. As a material for forming the second protective film 92, for example, photoresist or the like can be used.

Next, as shown in FIG. 8C, using the patterned second protective film 92 as a mask, the high refractive index portion 61 is dried by RIE using a fluorine-based gas such as _CF4 or a chlorine-based gas such as _Cl2 . Patterning is performed by etching to form a high refractive index portion 61 having a predetermined shape. Subsequently, the second protective film 92 is removed by wet etching using an organic solvent such as acetone.

Next, as shown in FIG. 8D, after forming a dielectric layer 60 and removing only the upper part of the waveguide part 40a as in the first embodiment, a p-side electrode 51 is placed above the waveguide part 40a. form.

Thereafter, the pad electrode 52 and the n-side electrode 80 are formed in the same manner as in each step of the manufacturing method of the first embodiment described using FIGS. 2G to 2H.

As described above, the nitride semiconductor laser device 1a according to this embodiment can be manufactured.

(Embodiment 3)
A nitride semiconductor laser device according to Embodiment 3 will be described. The nitride semiconductor laser device according to the present embodiment differs from the nitride semiconductor laser device 1 according to the first embodiment in that light absorption in the high refractive index portion is enhanced. The nitride semiconductor laser device according to the present embodiment will be described below with reference to FIGS. 9A and 9B, focusing on the differences from the nitride semiconductor laser device 1 according to the first embodiment.

9A and 9B are a schematic top view and a cross-sectional view, respectively, showing the configuration of a nitride semiconductor laser device 1b according to this embodiment. FIG. 9B shows a cross section of the nitride semiconductor laser device 1b taken along the line IXB--IXB in FIG. 9A. As shown in FIG. 9B, the nitride semiconductor laser device 1b according to this embodiment includes a substrate 10, a first semiconductor layer 20, a light emitting layer 30, a second semiconductor layer 40, an electrode member 50, and a dielectric It includes a body layer 60, a high refractive index section 144, and an n-side electrode 80. The second semiconductor layer 40 has a waveguide section 40a and a flat section 40b.

In this embodiment, an ion implantation region 144i is formed in the high refractive index portion 144. The ion implantation region 144i is a layer into which ions that absorb light generated in the light emitting layer 30 are implanted. Since light is absorbed in the ion implantation region 144i, the loss of higher-order modes passing outside the waveguide portion 40a can be increased, and the ratio of the fundamental mode can be increased. For example, B, N, Ar, Fe, Mg, Si, or the like can be used as the ion species to be implanted into the ion implantation region 144i. The ion implantation region 144i can be formed, for example, by forming the waveguide section 40a and the high refractive index section 144 and then implanting ions from above the high refractive index section 144. Note that the ion implantation region 144i may be formed not only in the high refractive index section 144 but also in the semiconductor layer located below the high refractive index section 144. Further, the ion implantation region 144i is formed not only in the high refractive index portion 144 made of a nitride semiconductor as in this embodiment, but also in the high refractive index portion 61 made of a dielectric material according to the invention according to the second embodiment. Good too.

(Embodiment 4)
A nitride semiconductor laser device according to Embodiment 4 will be described. The nitride semiconductor laser device according to the present embodiment differs from the nitride semiconductor laser device 1 according to the first embodiment in that it has a scattering portion that scatters higher-order modes. The nitride semiconductor laser device according to the present embodiment will be described below with reference to FIGS. 10A and 10B, focusing on the differences from the nitride semiconductor laser device 1 according to the first embodiment.

10A and 10B are a schematic top view and a cross-sectional view, respectively, showing the configuration of a nitride semiconductor laser device 1c according to this embodiment. FIG. 10B shows a cross section of the nitride semiconductor laser device 1c taken along the line XB-XB in FIG. 10A.

As shown in FIG. 10B, the nitride semiconductor laser device 1c according to this embodiment includes a substrate 10, a first semiconductor layer 20, a light emitting layer 30, a second semiconductor layer 40, an electrode member 50, and a dielectric It includes a body layer 60, a high refractive index section 44, and an n-side electrode 80. The second semiconductor layer 40 has a waveguide section 40a and a flat section 40b.

In this embodiment, the substrate 10 has a scattering section 11 having an uneven shape, which is disposed in a region of the main surface facing the first semiconductor layer 20 and located below the high refractive index section 44 . Since the scattering section 11 can scatter higher-order modes passing outside the waveguide section 40a, the higher-order modes included in the laser beam emitted from the front end surface Cf can be reduced. Therefore, the ratio of the fundamental mode included in the laser light emitted from the front end face Cf can be increased.

(Embodiment 5)
A nitride semiconductor laser device according to a fifth embodiment will be described. The nitride semiconductor laser device according to this embodiment is different from the nitride semiconductor laser device 1 according to the first embodiment in the shape of the waveguide portion. The nitride semiconductor laser device according to the present embodiment will be described below with reference to FIG. 11, focusing on the differences from the nitride semiconductor laser device 1 according to the first embodiment. FIG. 11 is a top view showing the configuration of a nitride semiconductor laser device 1d according to this embodiment. The nitride semiconductor laser device 1d according to this embodiment includes a waveguide section 240a and a high refractive index section 244. The waveguide section 240a is different from the waveguide section 40a according to the first embodiment in its shape when viewed from above. A recessed portion 240d is formed on a side surface of the waveguide portion 240a that intersects with the width direction. The waveguide section 240a has a rectangular recess 240d when viewed from above. Furthermore, the recesses 240d are arranged discretely in the resonator length direction. The width of the waveguide section 240a between adjacent recesses 240d is constant.

The high refractive index section 244 according to this embodiment is disposed in the recess 240d of the waveguide section 240a, and has a rectangular shape when viewed from above. In other words, the high refractive index portion 244 has a quadrangular prism shape.

The nitride semiconductor laser device 1d having such a configuration also provides the same effects as the nitride semiconductor laser device 1 according to the first embodiment.

The nitride semiconductor laser device according to the present disclosure can be used as a light source for image display devices, lighting, industrial equipment, etc., and is particularly useful as a light source for equipment that requires relatively high light output.

1, 1a, 1b, 1c, 1d, 1000 nitride semiconductor laser element 2 semiconductor laser device 10 substrate 11 scattering section 20 first semiconductor layer 30 light emitting layer 31 n-side optical guide layer 32 active layer 33 p-side optical guide layer 40 th 2 semiconductor layers 40a, 240a, 1040a waveguide section 40b flat section 40d, 240d concave section 41 electron barrier layer 42 p-side cladding layer 43 p-side contact layer 44, 61, 144, 244 high refractive index section 50 electrode member 51 p-side electrode 52 Pad electrode 60 Dielectric layer 80 N-side electrode 91 First protective film 92 Second protective film 100 Submount 101 Base 102a First electrode 102b Second electrode 103a First adhesive layer 103b Second adhesive layer 110 Wire 144i Ion implantation Area 1001 Rough optical waveguide mechanism 1002 Parallel smooth optical waveguide mechanism Cf Front end face Cr Rear end face

Claims (6)

A nitride semiconductor laser device that emits laser light,
A substrate and
a first semiconductor layer disposed above the substrate;
a light emitting layer disposed above the first semiconductor layer;
a second semiconductor layer disposed above the light emitting layer;
a dielectric layer disposed above the second semiconductor layer,
The second semiconductor layer has a ridge shape and includes a waveguide portion that guides the laser beam,
The waveguide section has a modulation section in which the width of the waveguide section is modulated with respect to a position in the resonator length direction, which is the longitudinal direction of the waveguide section,
The angle between the side surface of the modulation section that intersects with the width direction of the waveguide section and the longitudinal direction of the resonator is based on the film thickness and refractive index of the waveguide section and the layers laminated below it. defined by a calculated effective refractive index and an effective refractive index calculated based on the film thickness and refractive index of each of the dielectric layer disposed adjacent to the side surface and the layer laminated below it. is larger than the limit angle,
The nitride semiconductor laser element is formed on the side surface of the modulation section of the waveguide section, is disposed in a concave portion that is concave when viewed from above of the substrate, and is spaced apart from the waveguide section, and is located above the dielectric layer. It further includes a high refractive index section with a high refractive index,
The limit angle is the maximum value of the angle at which the laser beam propagating in the resonator length direction is totally reflected at the side surface,
The width of the waveguide section is a dimension of the waveguide section in a direction perpendicular to the resonator length direction and the thickness direction of the second semiconductor layer,
The dielectric layer is arranged between the waveguide section and the high refractive index section ,
The high refractive index section is not disposed outside the position where the width of the modulation section of the waveguide section is maximum when viewed from above of the substrate.
Nitride semiconductor laser device. The nitride semiconductor laser device according to claim 1, wherein a distance between the waveguide portion and the high refractive index portion in the width direction of the waveguide portion is 1 μm or more. The nitride semiconductor laser device according to claim 1 or 2, wherein the high refractive index portion is formed of a nitride semiconductor. The nitride semiconductor laser device according to claim 1, wherein the high refractive index portion is formed of a dielectric material. The nitride semiconductor laser device according to claim 1, wherein at least a portion of the high refractive index portion is an ion implantation region into which ions are implanted. 6. The substrate has a scattering portion having an uneven shape, the scattering portion being disposed in a region located below the high refractive index portion on the main surface facing the first semiconductor layer, and having an uneven shape. The nitride semiconductor laser device described in .

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