JP2021166255A - Semiconductor laser element - Google Patents

Abstract

To provide a semiconductor laser element in which the ripple in vertical FFP can be suppressed and the ratio of a basic mode can be increased.SOLUTION: A semiconductor laser element 1 includes a substrate 10, a first semiconductor layer 20 disposed over the substrate 10, a light-emitting layer 30 disposed above the first semiconductor layer 20, a second semiconductor layer 40 disposed above the light-emitting layer 30, and a low-refractive-index part 70 with a lower refractive index than the first semiconductor layer 20. The second semiconductor layer 40 includes a ridge part 40a for guiding the laser light generated in the light-emitting layer 30. The width of the ridge part 40a changes periodically in accordance with the position of the ridge part 40a in a waveguide direction. The angle between a side surface 40b of the ridge part 40a and the waveguide direction is larger than the limited angle that is defined based on the effective refractive index inside the ridge part 40a and outside the ridge part 40a. The low-refractive-index part 70 is disposed between the substrate 10 and an active layer 32 of the light-emitting layer 30 and at least outside the side surface 40b where the width of the ridge part 40a becomes small.SELECTED DRAWING: Figure 2

Description

The present invention relates to a semiconductor laser device and is suitable for use in, for example, processing a product.

In recent years, semiconductor laser devices have been used in the processing of various products. In such a semiconductor laser device, in order to improve the processing quality, the light emitted from the semiconductor laser device has a high output, and the high-order mode is cut as much as possible to increase the ratio of the basic mode. Is preferable.

The following Patent Document 1 includes a rough surface optical waveguide mechanism provided on both side walls of a striped ridge portion in the center of the waveguide direction, and a parallel sliding surface optical waveguide mechanism provided at both ends in the waveguide direction. The semiconductor laser element is described. The rough surface optical waveguide mechanism causes losses in higher-order modes and increases the proportion of basic modes.

Japanese Unexamined Patent Publication No. 9-2466664

However, in the configuration described in Patent Document 1, ripple (disturbance) may occur in the vertical FFP (Far-Field Pattern). In this case, since the shape of the emitted light greatly deviates from the ideal Gaussian shape, there arises a problem that the quality of the laser light emitted from the semiconductor laser element deteriorates.

In view of these problems, it is an object of the present invention to provide a semiconductor laser device capable of suppressing ripples in a vertical FFP and increasing the ratio of basic modes.

A main aspect of the present invention relates to a semiconductor laser device. The semiconductor laser device according to this embodiment is arranged above the substrate, the first semiconductor layer arranged above the substrate, the light emitting layer arranged above the first semiconductor layer, and above the light emitting layer. It includes a second semiconductor layer and a low refractive index portion having a refractive index lower than that of the first semiconductor layer. The second semiconductor layer has a ridge portion for guiding the laser beam generated in the light emitting layer, and the width of the ridge portion changes periodically according to the position of the ridge portion in the waveguide direction. The angle formed by the side surface of the ridge portion and the waveguide direction is larger than the limit angle defined by the effective refractive index inside the ridge portion and outside the ridge portion, and the low refractive index portion is the light emitting layer. It is arranged between the active layer and the substrate and at least outside the side surface where the width of the ridge portion is reduced.

According to the semiconductor laser element according to this aspect, the laser light of the higher-order mode is cut by setting the angle formed by the side surface of the ridge portion and the waveguide direction to be larger than the limit angle, and the laser light of the basic mode is used. The ratio is increased. Further, the low refractive index portion is arranged between the active layer of the light emitting layer and the substrate, and at least outside the side surface where the width of the ridge portion is reduced. As a result, the distribution position of the laser beam propagating in the ridge portion (waveguide) is less likely to move downward, so that ripple in the vertical FFP is suppressed. Therefore, it is possible to increase the ratio of the basic mode while suppressing the ripple in the vertical FFP.

As described above, according to the present invention, it is possible to provide a semiconductor laser device capable of suppressing ripple in a vertical FFP and increasing the ratio of basic modes.

The effects or significance of the present invention will be further clarified by the description of the embodiments shown below. However, the embodiments shown below are merely examples when the present invention is put into practice, and the present invention is not limited to those described in the following embodiments.

FIG. 1 is a top view schematically showing a configuration of a semiconductor laser device according to an embodiment. FIG. 2 is a cross-sectional view schematically showing the configuration of the semiconductor laser device according to the embodiment when the AA'cross section is viewed in the positive direction of the Y axis. 3A and 3B are cross-sectional views for explaining a method for manufacturing a semiconductor laser device according to an embodiment. 4 (a) and 4 (b) are cross-sectional views for explaining a method for manufacturing a semiconductor laser device according to an embodiment. 5 (a) and 5 (b) are cross-sectional views for explaining a method for manufacturing a semiconductor laser device according to an embodiment. 6 (a) and 6 (b) are cross-sectional views for explaining a method for manufacturing a semiconductor laser device according to an embodiment. 7 (a) and 7 (b) are cross-sectional views for explaining a method of manufacturing a semiconductor laser device according to an embodiment. 8 (a) and 8 (b) are cross-sectional views for explaining a method for manufacturing a semiconductor laser device according to an embodiment. 9 (a) and 9 (b) are cross-sectional views for explaining a method for manufacturing a semiconductor laser device according to an embodiment. 10 (a) and 10 (b) are cross-sectional views for explaining a method for manufacturing a semiconductor laser device according to an embodiment. FIG. 11 is a cross-sectional view schematically showing the configuration of the semiconductor laser device according to the embodiment. FIG. 12 is a top view schematically showing each size of the side surface of the ridge portion according to the embodiment. FIG. 13A is a graph showing the relationship between the difference in refractive index inside and outside the ridge portion and the limit angle according to the embodiment. FIG. 13B is a graph showing the relationship between the predetermined distance of the side surface in the Y-axis direction and the minimum value of the width of the side surface in the X-axis direction according to the embodiment. FIG. 14A is a top view schematically showing the configuration of the semiconductor laser device according to Comparative Example 1. 14 (b) and 14 (c) are cross-sectional views schematically showing the configurations of the semiconductor laser according to Comparative Example 1 when the A11-A12 cross section and the A21-A22 cross section are viewed in the positive Y-axis direction, respectively. be. FIG. 15 is a top view schematically showing the configuration of the semiconductor laser device according to Comparative Example 2. FIG. 16 is a graph showing the experimental results of vertical FFP when the structure of each ridge portion of the semiconductor laser device is changed according to Comparative Examples 1 and 2. FIG. 17A is a top view schematically showing the configuration of the semiconductor laser device according to the embodiment. 17 (b) and 17 (c) are cross-sectional views schematically showing the configurations of the semiconductor laser according to the embodiment when the A31-A32 cross section and the A41-A42 cross section are viewed in the positive Y-axis direction, respectively. .. FIG. 18A is a cross-sectional view schematically showing the configuration of the semiconductor laser device according to the first modification. FIG. 18B is a cross-sectional view schematically showing the configuration of the semiconductor laser device according to the second modification. FIG. 19A is a cross-sectional view schematically showing the configuration of the semiconductor laser device according to the third modification. FIG. 19B is a cross-sectional view schematically showing the configuration of the semiconductor laser device according to the fourth modification. FIG. 20 is a cross-sectional view schematically showing the configuration of the semiconductor laser device according to the modified example 5. FIG. 21 is a top view schematically showing the configuration of the semiconductor laser device according to the modified example 6. FIG. 22 is a top view schematically showing the configuration of the semiconductor laser device according to the modified example 7.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. For convenience, the X, Y, and Z axes that are orthogonal to each other are added to each figure. The X-axis direction is the width direction of the ridge portion, and the Y-axis direction is the light propagation direction (resonator length direction) in the ridge portion. The Z-axis direction is the stacking direction of each layer constituting the semiconductor laser device, and the Z-axis positive direction is the upward direction.

FIG. 1 is a top view schematically showing the configuration of the semiconductor laser device 1.

The semiconductor laser device 1 is provided with a ridge portion 40a extending linearly in the Y-axis direction near the center in the X-axis direction. The ridge portion 40a forms a waveguide WG that guides the laser beam. The ridge portion 40a propagates the laser light generated in the light emitting layer 30 (see FIG. 2) and oscillating in the semiconductor laser element 1 along the ridge portion 40a. Side surfaces 40b are provided at the ends of the ridge portion 40a on the positive side of the X-axis and the negative side of the X-axis, respectively. In top view, the width of the ridge portion 40a changes periodically according to the waveguide direction (Y-axis direction) of the ridge portion 40a because the side surface 40b forms an angle θa or an angle θb with respect to the YZ plane. doing.

A low refractive index portion 70 is provided on the outside of the portion of the ridge portion 40a having a narrow width in the X-axis direction. The low refractive index portion 70 has a triangular shape when viewed from above, and the width of the low refractive index portion 70 in the X-axis direction differs depending on the position in the Y-axis direction. At the position in the Y-axis direction where the width of the ridge portion 40a in the X-axis direction is small, the width of the low refractive index portion 70 in the X-axis direction is large. The position of the low refractive index portion 70 in the Z-axis direction will be described later with reference to FIG. 2, and the effect of the low refractive index portion 70 will be described later with reference to FIGS. 17 (a) to 17 (c). ..

The end face 1a is an end face of the ridge portion 40a located on the positive side of the Y-axis, and is an end face on the emission side of the semiconductor laser element 1. The end face 1b is an end face of the ridge portion 40a located on the negative side of the Y-axis, and is an end face on the reflection side of the semiconductor laser element 1. An end face coating film is formed on the end faces 1a and 1b. When the light (forward wave) heading from the end face 1b side to the end face 1a reaches the end face 1a, a part of the forward wave is emitted from the end face 1a in the positive direction of the Y axis as emitted light, and a part of the forward wave is on the end face 1a. It is reflected and becomes light (backward wave) heading from the end face 1a side to the end face 1b. The receding wave travels in the negative direction of the Y-axis through the ridge portion 40a, and when it reaches the end face 1b, most of the receding wave is reflected by the end face 1b and becomes a forward wave. In this way, the light generated in the semiconductor laser element 1 is amplified between the end face 1a and the end face 1b and emitted from the end face 1a.

FIG. 2 is a cross-sectional view schematically showing a configuration when the AA'cross section of the semiconductor laser device 1 shown in FIG. 1 is viewed in the positive direction of the Y axis.

As shown in FIG. 2, the semiconductor laser device 1 includes a substrate 10, a first semiconductor layer 20, a light emitting layer 30, a second semiconductor layer 40, an electrode member 50, a dielectric layer 60, and a low refractive index. A portion 70 and an n-side electrode 80 are provided.

The first semiconductor layer 20 is arranged above the substrate 10. The first semiconductor layer 20 is an n-side clad layer. The first semiconductor layer 20 is formed by laminating the first n-side semiconductor layer 20a and the second n-side semiconductor layer 20b (see FIG. 5B).

The light emitting layer 30 is arranged above the first semiconductor layer 20. The light emitting layer 30 has a laminated structure in which the n-side light guide layer 31, the active layer 32, and the p-side light guide layer 33 are laminated in this order from the bottom. When a voltage is applied to the semiconductor laser device 1, light is generated and propagated in the light emitting layer 30.

The second semiconductor layer 40 is arranged above the light emitting layer 30. The second semiconductor layer 40 has a laminated structure in which the electron barrier layer 41, the p-side clad layer 42, and the p-side contact layer 43 are laminated in this order from the bottom.

A ridge portion 40a is formed on the upper portion of the second semiconductor layer 40 near the center in the X-axis direction. The ridge portion 40a has a shape protruding in the positive direction of the Z axis, and has a ridge shape (protrusion shape) extending in the Y axis direction. By forming the ridge portion 40a, the waveguide WG is formed corresponding to the range of the ridge portion 40a in the X-axis direction. Further, by forming the ridge portion 40a, side surface 40b is formed at each of the end portion on the positive side of the X-axis and the end portion on the negative side of the X-axis of the ridge portion 40a. Further, a flat portion 40c extending in the X-axis direction from the root of the ridge portion 40a is formed on the upper portion of the second semiconductor layer 40.

The electrode member 50 is arranged above the second semiconductor layer 40. The electrode member 50 includes a p-side electrode 51 for applying a voltage and a pad electrode 52 arranged above the p-side electrode 51. The p-side electrode 51 is arranged on the upper surface of the ridge portion 40a. The p-side electrode 51 is an ohmic electrode that makes ohmic contact with the p-side contact layer 43 above the p-side contact layer 43. The pad electrode 52 has a shape longer than the ridge portion 40a in the X-axis direction, and is in contact with the p-side electrode 51 and the dielectric layer 60.

The dielectric layer 60 is arranged above the p-side clad layer 42 on the outside of the ridge portion 40a in the X-axis direction in order to confine light in the ridge portion 40a. Specifically, the dielectric layer 60 is continuously formed from the side surface 40b to the flat portion 40c. The dielectric layer 60 is formed of an insulating film having a refractive index lower than that of the ridge portion 40a.

The low refractive index portion 70 is arranged inside the first semiconductor layer 20 in the Z-axis direction and outside the ridge portion 40a in the X-axis direction. The low refractive index portion 70 is made of a material having a refractive index lower than that of the first semiconductor layer 20, the light emitting layer 30, and the second semiconductor layer 40. In the present embodiment, the low refractive index portion 70 is made of a dielectric material made of a silicon oxide film. According to the low refractive index unit 70, it is possible to suppress the occurrence of ripple (turbulence) in the vertical FFP, as will be described later with reference to FIGS. 17 (a) to 17 (c). Further, in the present embodiment, since the cross section of the low refractive index portion 70 has a rectangular shape, the inner end portion and the outer end portion of the low refractive index portion 70 in the X-axis direction are parallel to the Z-axis direction. As a result, an interface is formed in each layer in the vicinity of the position P1 of the inner end portion and the vicinity of the position P2 of the outer end portion as shown by the broken line, and the laser light of the higher-order mode is scattered by this interface.

The n-side electrode 80 is an ohmic electrode that is arranged below the substrate 10 and makes ohmic contact with the substrate 10.

Next, a method of manufacturing the semiconductor laser device 1 will be described with reference to FIGS. 3 (a) to 10 (b). 3 (a) to 10 (b) are cross-sectional views similar to those in FIG.

Hereinafter, in the growth of each layer, for example, trimethylgallium (TMG), trimethylammonium (TMA) and trimethylindium (TMI) are used as the organometallic raw materials containing Ga, Al and In, respectively. _{Ammonia (NH 3} ) is used as a nitrogen raw material. As the lithography method, a photolithography method using a short wavelength light source, an electron beam lithography method for drawing directly with an electron beam, a nanoimprint method, or the like can be used. As the etching method, for example, dry etching by reactive ion etching (RIE) using a fluorine-based gas such as _{CF 4, or wet etching using hydrofluoric acid (HF) diluted to about 1:10, etc.} Can be used.

As shown in FIG. 3A, a metalorganic chemical vapor deposition (MOCVD method) is performed on a substrate 10 which is an n-type hexagonal GaN substrate whose main surface is the (0001) plane. The n-side semiconductor layer 20a of 1 is formed. Specifically, an n-side clad layer made of n-type AlGaN is grown by 3 μm as the first n-side semiconductor layer 20a on the substrate 10 having a thickness of 400 μm.

Next, as shown in FIG. 3B, the low refractive index portion 70 is formed on the first n-side semiconductor layer 20a. _{Specifically, a silicon oxide film (SiO 2} ) is formed on the first n-side semiconductor layer 20a as a low refractive index portion 70 by a plasma CVD (Chemical Vapor Deposition) method using _{silane (SiH 4).} A 100 nm film is formed. The film forming method of the low refractive index portion 70 is not limited to the plasma CVD method, and a known film forming method such as a thermal CVD method, a sputtering method, a vacuum vapor deposition method, or a pulse laser deposition method is used. be able to. Subsequently, a first protective film 91 made of a photoresist is formed on the low refractive index portion 70.

Next, as shown in FIG. 4A, patterning is performed so that the first protective film 91 remains only in a desired place by using a photolithography method. That is, the first protective film 91 is selectively removed so that the first protective film 91 remains in a predetermined shape. The predetermined shape is the shape of the low refractive index portion 70 shown in FIG. 1 in a top view.

Next, as shown in FIG. 4B, the low refractive index portion 70 is etched using the first protective film 91 as a mask.

Next, as shown in FIG. 5A, the first protective film 91 is removed. An organic solvent such as acetone can be used to remove the first protective film 91.

Next, as shown in FIG. 5B, a second n-side semiconductor layer 20b is formed on the first n-side semiconductor layer 20a and the low refractive index portion 70. Specifically, as the second n-side semiconductor layer 20b, an n-side clad layer made of n-type AlGaN is grown by 0.2 μm. As a result, the formation of the first semiconductor layer 20 is completed, and the low refractive index portion 70 is positioned in the first semiconductor layer 20.

Here, the crystal growth state on the low refractive index portion 70 can be controlled by the growth conditions of the second n-side semiconductor layer 20b. For example, by raising the growth temperature to a high temperature, diffusion of the raw material is likely to occur, crystal growth in the lateral direction (X-axis direction) is promoted, and the nitride semiconductor layer is relatively flat even on the low refractive index portion 70. Can be formed into.

When the second n-side semiconductor layer 20b is formed, crystals grown from the left and right (X-axis direction) of the low refractive index portion 70 grow so as to cover the low refractive index portion 70, and the low refractive index portion 70 is formed. Join on 70. This bonding creates an interface at the second n-side semiconductor layer 20b located directly above the low refractive index portion 70, and defects are introduced at this interface. As a result, the defect density of the second n-side semiconductor layer 20b arranged directly above the low refractive index portion 70 is larger than the defect density of the second n-side semiconductor layer 20b other than directly above the low refractive index portion 70. Become.

As described above, when a defect is introduced at the interface of the second n-side semiconductor layer 20b located directly above the low refractive index portion 70, similarly, in each layer laminated above the first semiconductor layer 20 as well. An interface is formed immediately above the low refractive index portion 70, and defects are introduced at this interface. As a result, in each layer above the first semiconductor layer 20, the defect density directly above the low refractive index portion 70 becomes higher than the defect density other than directly above the low refractive index portion 70. In particular, when a defect is introduced in the light emitting layer 30 directly above the low refractive index portion 70, unnecessary higher-order mode light distributed in the vicinity of the light emitting layer 30 directly above the low refractive index portion 70 can be weakened.

Next, as shown in FIG. 6A, the light emitting layer 30 and the second semiconductor layer 40 are sequentially formed on the first semiconductor layer 20 by using the organometallic vapor layer growth method. Specifically, the n-side optical guide layer 31 made of n-type GaN is grown by 0.2 μm. Subsequently, the active layer 32 composed of two cycles of the barrier layer made of InGaN and the InGaN quantum well layer is grown. Subsequently, the p-side optical guide layer 33 made of p-type GaN is grown by 0.1 μm. Subsequently, the electron barrier layer 41 made of AlGaN is grown by 10 nm. Subsequently, a p-side clad layer 42 composed of a strained superlattice having a thickness of 0.66 μm formed by repeating 220 cycles of a p-type AlGaN layer having a film thickness of 1.5 nm and a p-type GaN layer having a film thickness of 1.5 nm is grown. Let me. Subsequently, the p-side contact layer 43 made of p-type GaN is grown by 0.05 μm.

Next, as shown in FIG. 6B, a second protective film 92 is formed on the second semiconductor layer 40. _{Specifically, a silicon oxide film (SiO 2} ) is formed on the second semiconductor layer 40 as the second protective film 92 by a plasma CVD method using _{silane (SiH 4} ) at 300 nm. The film-forming material of the second protective film 92 is not limited to the above, and may be any material that is selective for etching of the second semiconductor layer 40, which will be described later, such as a dielectric or a metal. ..

Next, as shown in FIG. 7A, the second protective film 92 is selectively removed so that the second protective film 92 remains in a predetermined shape by using a photolithography method and an etching method. The predetermined shape is the shape of the ridge portion 40a shown in FIG. 1 in a top view. That is, the predetermined shape is a band-shaped shape whose width changes with respect to the position in the Y-axis direction (resonator length direction) in the top view.

Next, as shown in FIG. 7B, the second semiconductor layer 40 is formed by etching the p-side contact layer 43 and the p-side clad layer 42 using the second protective film 92 formed in a predetermined shape as a mask. A ridge portion 40a and a flat portion 40c are formed on the surface.

Specifically, the ridge portion 40a is formed below the second protective film 92 located at the center in the X-axis direction. The ridge portion 40a is composed of a convex portion of the p-side clad layer 42 protruding in the positive direction of the Z-axis and a p-side contact layer 43 on the convex portion. Further, the flat portion 40c is formed by etching the p-side contact layer 43 and the p-side clad layer 42 in the region where the second protective film 92 is not formed. As the etching of the p-side contact layer 43 and the p-side clad layer 42, dry etching by the RIE method using a chlorine-based gas such _{as Cl 2 may be used.}

The height of the ridge portion 40a in the Z-axis direction is not particularly limited, but as an example, it is 100 nm or more and 1 μm or less. In order to operate the semiconductor laser device 1 with a high light output (for example, watt class), the height of the ridge portion 40a may be set to 300 nm or more and 800 nm or less. In this embodiment, the height of the ridge portion 40a is 650 nm.

Since the ridge portion 40a is formed by using the second protective film 92 formed in a predetermined shape as a mask, the width of the side surface 40b of the ridge portion 40a in the X-axis direction is the Y-axis as shown in the top view of FIG. It has a band-like shape that changes with respect to the position in the direction (resonator length direction).

Next, as shown in FIG. 8A, the second protective film 92 is removed by wet etching using hydrofluoric acid or the like.

Next, as shown in FIG. 8B, the dielectric layer 60 is formed so as to cover the p-side contact layer 43 and the p-side clad layer 42. As a result, the dielectric layer 60 is formed on the ridge portion 40a and the flat portion 40c. As the dielectric layer 60, for example, a silicon oxide film (SiO ₂ ) is formed into a film of 300 nm _{by a plasma CVD method using silane (SiH 4).}

Next, a third protective film 93 made of a photoresist is formed on the dielectric layer 60 shown in FIG. 8 (b). Subsequently, the third protective film 93 is selectively removed so that the third protective film 93 remains only on the flat portion 40c. Subsequently, as shown in FIG. 9A, only the dielectric layer 60 on the ridge portion 40a is removed by wet etching using hydrofluoric acid using the third protective film 93 as a mask, and p. The upper surface of the side contact layer 43 is exposed. Subsequently, the third protective film 93 is removed. An organic solvent such as acetone can be used to remove the third protective film 93.

Next, as shown in FIG. 9B, the p-side electrode 51 made of Pd / Pt is formed only on the ridge portion 40a by using the vacuum deposition method and the lift-off method. Specifically, the p-side electrode 51 is formed on the p-side contact layer 43 exposed from the dielectric layer 60. The film forming method of the p-side electrode 51 is not limited to the vacuum vapor deposition method, and may be a sputtering method, a pulse laser film forming method, or the like. The electrode material of the p-side electrode 51 may be a material that makes ohmic contact with the second semiconductor layer 40 (p-side contact layer 43), such as Ni / Au-based or Pt-based.

Next, as shown in FIG. 10A, the pad electrode 52 is formed so as to cover the p-side electrode 51 and the dielectric layer 60. Specifically, a negative resist is patterned in a portion other than the portion to be formed by a photolithography method or the like, and a pad electrode 52 made of Ti / Pt / Au is formed on the entire upper surface of the substrate 10 by a vacuum vapor deposition method or the like to lift off. Use the method to remove unnecessary electrodes. As a result, the pad electrode 52 having a predetermined shape can be formed on the p-side electrode 51 and the dielectric layer 60. In this way, the electrode member 50 composed of the p-side electrode 51 and the pad electrode 52 is formed. Subsequently, the lower surface of the substrate 10 is polished with a diamond slurry to thin the substrate 10 until the thickness of the substrate 10 is about 100 μm.

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

Next, the semiconductor laser device that has completed the manufacturing process up to FIG. 10B is cleaved (primary cleaved) along the m-plane so that the length in the m-axis direction is, for example, 2000 μm. Subsequently, for example, using an electron cyclotron resonance (ECR) sputtering method, a front coat film is formed on the cleavage surface that emits laser light to form an end surface 1a, and a rear coat film is formed on the cleavage surface on the opposite side. It is formed to form the end face 1b. The reflectance of the end faces 1a and 1b is set by adjusting the material, composition, film thickness and the like of the coating film. Here, in order to obtain highly efficient laser characteristics, the reflectance of the end face 1a on the front side is set to 5%, and the reflectance of the end face 1b on the rear side is set to 95%. The reflectance of the end face 1a is preferably set to about 0.1% to 18%, and the reflectance of the end face 1b is preferably set to 90% or more.

Subsequently, the primary cleaved semiconductor light emitting device is cleaved (secondary cleaved) so that, for example, the length in the Y-axis direction has a pitch of 400 μm. In this way, the semiconductor laser device 1 shown in FIGS. 1 and 2 is completed.

FIG. 11 is a cross-sectional view schematically showing the configuration of the semiconductor laser device 2 on which the semiconductor laser element 1 is mounted. FIG. 11 shows a state in which the semiconductor laser element 1 of FIG. 2 is turned upside down (a state in which the Z-axis positive direction is downward).

The semiconductor laser device 2 includes a semiconductor laser element 1 and a submount 100, and is used, for example, for processing a product. The submount 100 has 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 arranged on the Z-axis positive side of the substrate 10 of the semiconductor laser element 1 and functions as a heat sink. The material of the base 101 is not particularly limited, but is limited to ceramics such as aluminum nitride (AlN) and silicon carbide (SiC), and metals such as diamond (C), Cu, and Al formed by CVD. It may be composed of a single material or a material having a thermal conductivity equal to or higher than that of the semiconductor laser element 1, such as an alloy such as CuW.

The first electrode 102a is arranged on the Z-axis negative side surface of the base 101, and the second electrode 102b is arranged on the Z-axis positive side surface of the base 101. The first electrode 102a and the second electrode 102b are laminated films composed of three metal films, for example, Ti having a film thickness of 0.1 μm, Pt having a film thickness of 0.2 μm, and Au having a film thickness of 0.2 μm.

The first adhesive layer 103a is arranged on the Z-axis negative side surface of the first electrode 102a, and the second adhesive layer 103b is arranged on the Z-axis positive side surface of the second electrode 102b. The first adhesive layer 103a and the second adhesive layer 103b are, for example, eutectic solders made of gold-tin alloys containing Au and Sn at 70% and 30%, respectively.

The semiconductor laser element 1 is mounted on the submount 100 so that the p side (electrode member 50 side) of the semiconductor laser element 1 is connected to the submount 100. That is, the mounting embodiment of FIG. 11 is a junction-down mounting, in which the pad electrode 52 of the semiconductor laser element 1 is connected to the first adhesive layer 103a of the submount 100.

Further, the wire 110 is connected to the n-side electrode 80 of the semiconductor laser element 1 and the first electrode 102a of the submount 100 by wire bonding, respectively. As a result, a voltage can be applied to the semiconductor laser element 1 via the wire 110.

The semiconductor laser device 2 shown in FIG. 11 has a form in which the p side (electrode member 50 side) of the semiconductor laser element 1 is connected to the submount 100 (junction down mounting), but the semiconductor laser is not limited to this. The n-side electrode 80 of the element 1 may be connected to the submount 100 (junction-up mounting). Further, the semiconductor laser device 2 may have a form in which separate submounts are connected to both the electrode member 50 and the n-side electrode 80.

Next, the shape of the side surface 40b of the ridge portion 40a will be described with reference to FIGS. 12 to 13 (b).

FIG. 12 is a schematic view showing each size of the side surface 40b of the ridge portion 40a. FIG. 12 is a top view schematically showing the configuration of the semiconductor laser device 1 as in FIG. 1.

The width of the ridge portion 40a in the X-axis direction (hereinafter, simply referred to as “width”) changes continuously and periodically according to the position in the Y-axis direction (waveguide direction), and the wide portion and the width. The narrow portions of are alternately arranged in the Y-axis direction.

Here, the maximum value of the width of the ridge portion 40a is Wa, and the minimum value of the width of the ridge portion 40a is Wb. La is the distance in the Y-axis direction from the position where the width of the ridge portion 40a is the maximum value Wa to the position where the width of the ridge portion 40a is the minimum value Wb and which is adjacent to the positive side of the Y-axis. Let Lb be the distance in the Y-axis direction from the position where the width of the ridge portion 40a is the maximum value Wa to the position where the width of the ridge portion 40a is the minimum value Wb and which is adjacent to the negative side of the Y-axis. The side surface 40b extending from the position where the width of the ridge portion 40a becomes the maximum value Wa to the position where the width of the ridge portion 40a becomes the minimum value Wb has a linear shape in the top view. Let θa be the angle between the side surface 40b extending toward the positive side of the Y-axis from the position where the width of the ridge portion 40a becomes the maximum value Wa and the Y-axis direction. Let θb be the angle between the side surface 40b extending from the position where the width of the ridge portion 40a becomes the maximum value Wa toward the negative side of the Y-axis and the Y-axis direction.

The relationship between θa, θb, Wa, Wb, La, and Lb is expressed by the following equations (1) and (2).

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

In the present embodiment, the angles θa and θb are both set to be larger than the limit angle θc. The limit angle θc is the maximum value of the angle at which the laser beam is totally reflected on the side surface 40b of the ridge portion 40a. That is, the angles θa and θb are set so as to satisfy the following equation (3).

θa> θc and θb> θc ... (3)

When the angles θa and θb are set to be larger than the limit angle θc, it is possible to reduce the light in the higher-order mode and increase the ratio of the light in the basic mode as described later with reference to FIG. 14 (a). can.

Next, a setting example of Wa, Wb, La, Lb, θa, and θb will be described.

For example, the width of the ridge portion 40a is 1 μm or more and 100 μm or less. In order to operate the semiconductor laser device 1 with a high light output (for example, watt class), the maximum value Wa of the width of the ridge 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 ridge portion 40a, the more the higher-order mode component can be reduced. However, if it becomes too small, the basic mode component (basic transverse mode component) is also reduced due to loss. On the other hand, when the minimum value Wb of the width of the ridge portion 40a is increased, the effect of reducing the higher-order mode component becomes smaller. In order to efficiently suppress higher-order mode components while maintaining the strength of the basic mode, the minimum value Wb of the width of the ridge portion 40a is set to about 1/4 or more and 3/4 or less of the maximum value Wa of the width. You may.

Further, when the distances La and Lb are reduced, the angles θa and θb are increased, so that the above equation (3) is easily satisfied. On the other hand, if the distances La and Lb are made too large, the number of portions where the width of the ridge portion 40a is narrowed within the range of the length of the semiconductor laser element 1 in the Y-axis direction is reduced, so that the effect of suppressing the higher-order mode is obtained. It becomes smaller. In this embodiment, Wa = 16 μm, Wb = 10 μm, and La = Lb = 30 μm. At this time, θa = θb = 5.7 °.

Further, La ≠ Lb may be satisfied as long as the conditions of the above equations (1) and (2) are satisfied. If La ≠ Lb, the loss to the higher-order mode can be made different between the outward path and the return path while the light reciprocates in the resonator in the Y-axis direction. For example, if La> Lb, the loss to the higher-order mode when the light travels from the end face 1b to the end face 1a can be increased.

Further, as described above, the low refractive index portion 70 made of a silicon oxide film is arranged on the outside of the side surface 40b of the ridge portion 40a. Here, assuming that the ridge portion 40a and the low refractive index portion 70 are separated by a certain distance Dd in the width direction (X-axis direction) of the ridge portion 40a, the low refractive index portion 70 is outside the ridge portion 40a. In order to give an effect to the propagating light, it is necessary to satisfy the following equation (4).

Wb + 2 × Dd <Wa… (4)

Here, if the distance Dd is too small, the proportion of the basic mode components affected by the low refractive index portion 70 increases, and the loss in the basic mode increases. Therefore, the distance Dd needs to be increased to some extent. As a result of the study by the inventors, the loss of the basic mode component can be suppressed when the distance Dd is 1 μm or more. Further, in the X-axis direction, the end portion of the low refractive index portion 70 opposite to the ridge portion 40a is at the same position as or outside the position of the side surface 40b of the ridge portion 40a having the maximum width Wa. May be good. In the present embodiment, Dd = 2 μm, and the end portion of the low refractive index portion 70 opposite to the ridge portion 40a in the X-axis direction is the same as the position of the side surface 40b of the ridge portion 40a having the maximum width Wa. be.

Next, how to obtain the limit angle θc will be described.

In the following method, the structure of the three-dimensional ridge portion 40a is approximated by the two-dimensional slab waveguide structure by using the equivalent refractive index method. At the central position of the ridge portion 40a in the X-axis direction, the equivalent refractive index ni at this position is calculated using the thickness and refractive index of each layer. Similarly, at the central position of the low refractive index portion 70 in the X-axis direction, the equivalent refractive index no at this position is calculated using the thickness and refractive index of each layer. The equivalent refractive index ni is the effective refractive index inside the ridge portion 40a, and the equivalent refractive index no is the effective refractive index outside the ridge portion 40a. In this embodiment, ni> no is always satisfied by the formation of the ridge portion 40a.

Next, using Snell's law, the maximum value of the angle when the total reflection condition is satisfied, that is, the limit angle θc is calculated. The limit angle θc is calculated by the following equation (4).

θc = 90 ° -arcsin (no / ni) ... (5)

For example, assuming that ni = 2.535 and no = 2.527, θc = 4.6 ° is calculated based on the above equation (5). Using θc calculated in this way, Wa, Wb, La, and Lb are set so that the above equations (1) to (3) are satisfied.

Next, an example of a procedure for actually determining each setting value will be described.

FIG. 13A is a graph showing the relationship between the difference in refractive index (ni—no) inside and outside the ridge portion 40a and the limit angle θc. In FIG. 13A, the horizontal axis represents the refractive index difference (ni-no), and the vertical axis represents the limit angle θc. The graph of FIG. 13A is created based on the above equation (5).

When the equivalent refractive indexes ni and no are calculated using the thickness and the refractive index of each layer as described above, the limit angle θc can be calculated based on the graph of the above formula (5) or FIG. 13 (a).

FIG. 13B shows the above when the maximum value Wa is fixed at 16 μm and the limit angle θc is 2.6 °, 3.6 °, 4.6 °, 5.6 °, and 6.6 °. It is a graph which shows the relationship between the distance La satisfying the equation (3), and the local minimum value Wb. In FIG. 13B, the horizontal axis represents the distance La and the vertical axis represents the minimum value Wb.

The condition of the above formula (3) is satisfied in the region below each straight line in FIG. 13 (b). Therefore, the angle θa can be set larger than the limit angle θc by setting the minimum value Wb and the distance La so as to be included in the region below the straight line corresponding to the limit angle θc. Similarly, for the distance Lb, the angle θb can be set larger than the limit angle θc by setting the minimum value Wb and the distance Lb so as to be included in the region below the straight line corresponding to the limit angle θc.

In this way, the limit angle θc can be calculated based on the equivalent refractive indexes ni and no inside and outside the ridge portion 40a, and the maximum value Wa, the minimum value Wb, the distance La, and Lb can be set based on the calculated θc. As a result, the above equation (3) is satisfied, so that the light in the higher-order mode can be reduced.

Next, the advantages and disadvantages of Comparative Examples 1 and 2 will be described with reference to Comparative Example 1 shown in FIGS. 14A to 14C and Comparative Example 2 shown in FIG.

FIG. 14A is a top view schematically showing the configuration of the semiconductor laser device according to Comparative Example 1. A graph schematically showing an example of light distribution in the basic mode and the higher-order mode in the X-axis direction is added to the lower side of FIG. 14A.

In Comparative Example 1, the low refractive index portion 70 is omitted as compared with the above embodiment. In the semiconductor laser device of Comparative Example 1, light propagates in the ridge portion 40a in the Y-axis direction during laser oscillation. At this time, since the total reflection condition is not satisfied inside and outside the ridge portion 40a (because the above equation (3) is satisfied), even if there is a narrow portion of the ridge portion 40a, the light propagates in the Y-axis direction. do. In FIG. 14A, the state of light propagation is indicated by a broken line arrow. In the portion where the width of the ridge portion 40a is narrowed, the light travels slightly inward due to the influence of the refractive index difference between the inside and outside of the ridge portion 40a, but since the total reflection condition is not satisfied, most of the light is outside the ridge portion 40a. Proceed in the Y-axis direction while passing through.

Here, the light propagating in the ridge portion 40a includes the light of the basic mode and the higher-order mode shown in the lower graph of FIG. 14A. When the above formula (3) is satisfied as in Comparative Example 1, the light component of the higher-order mode is lost due to the side surface 40b of the ridge portion 40a, and the ratio of the basic mode can be increased.

14 (b) and 14 (c) schematically show the configurations of the semiconductor laser of Comparative Example 1 shown in FIG. 14 (a) when the A11-A12 cross section and the A21-A22 cross section are viewed in the positive Y-axis direction, respectively. It is sectional drawing which shows. For convenience, only the substrate 10, the first semiconductor layer 20, the active layer 32, and the second semiconductor layer 40 are shown in FIGS. 14 (b) and 14 (c).

As shown in FIG. 14B, at a position where the width of the ridge portion 40a is wide, as shown in the light distribution DL1 in the basic mode, the semiconductor so that the light propagating in the ridge portion 40a is confined in the vicinity of the active layer 32. A laser element is configured. In this case, the light propagating in the ridge portion 40a is less likely to be applied to the substrate 10.

However, as shown in FIG. 14C, at a position where the width of the ridge portion 40a is narrow, as shown in the light distribution DL2 in the basic mode, the light propagating outside the ridge portion 40a is outside the ridge portion 40a. Since the thickness of the p-side clad layer 42 is thin, it is pushed down toward the substrate 10. Therefore, a higher-order mode in the vertical direction called a substrate mode is excited between the active layer 32 and the first semiconductor layer 20 and between the first semiconductor layer 20 and the substrate 10. When this substrate mode occurs, ripple occurs in the vertical FFP. Such ripples are particularly increased by higher order modes having a light intensity peak on the outside of the ridge 40a.

FIG. 15 is a top view schematically showing the configuration of the semiconductor laser device according to Comparative Example 2. In FIG. 15, a graph schematically showing an example of light distribution in the basic mode and the higher-order mode in the X-axis direction is added.

In Comparative Example 2, as compared with the above embodiment, the low refractive index portion 70 is omitted, and the ridge portion 200 is formed on the upper portion of the second semiconductor layer 40 in place of the ridge portion 40a. Further, in Comparative Example 2, the total reflection condition is satisfied inside and outside the ridge portion 200. That is, in Comparative Example 2, θa <θc and θb <θc are satisfied instead of the above equation (3).

In Comparative Example 2, since the above equation (3) is not satisfied, it is not possible to reduce the light in the higher-order mode in the form as in Comparative Example 1. However, in Comparative Example 2, the ripple in the vertical FFP that occurred in the case of Comparative Example 1 can be suppressed.

In the semiconductor laser element of Comparative Example 2, since the difference in refractive index inside and outside the ridge portion 200 satisfies the total reflection condition, as shown by the broken line arrow in FIG. 15, the light inside the ridge portion 200 is one of the ridge portions 200. The light reflected by the side surface 201 is transmitted to the outside of the ridge portion 200 through the other side surface 201 of the ridge portion 200. That is, since the light emitted to the outside of the semiconductor laser element as laser light does not propagate outside the ridge portion 200, the substrate mode generated in Comparative Example 1 is suppressed by the structure of the ridge portion 200 of Comparative Example 2. Therefore, according to the semiconductor laser device of Comparative Example 2, ripple in the vertical FFP can be suppressed.

FIG. 16 is a graph showing the experimental results of vertical FFP when the structure of each ridge portion of the semiconductor laser device is changed according to Comparative Examples 1 and 2.

In this experiment, with reference to FIG. 12 showing the size of each part, La = Lb and Wa = 16 μm were fixed, and the distance La was changed in the range of 15 μm to 90 μm at 15 μm intervals. Further, the minimum width value Wb was changed in the range of 4 μm to 10 μm at intervals of 2 μm. Further, in this experiment, as in Comparative Examples 1 and 2, the low refractive index portion 70 was not provided.

FIG. 16 shows a vertical FFP when the light output is 1 W in the semiconductor laser device having each of these structures. In each graph of FIG. 16, the vertical axis shows the standardized light intensity at the maximum value, and the horizontal axis shows the standardized angle. Further, FIG. 16 is based on a graph of a vertical FFP based on the semiconductor laser device of Comparative Example 1 satisfying the relationship of the above formula (3) and a semiconductor laser device of Comparative Example 2 not satisfying the relationship of the above formula (3). The graph of the vertical FFP is separated by a broken line.

As shown in the graph on the left side of the broken line, it can be seen that in the semiconductor laser device (Comparative Example 1) satisfying θa> θc and θb> θc, ripple (turbulence) occurs in the vertical FFP. On the other hand, as shown in the graph on the right side of the broken line, it can be seen that in the semiconductor laser device (Comparative Example 2) satisfying θa <θc and θb <θc, ripple does not occur in the vertical FFP. Further, it can be seen that the ripple intensity increases as the width minimum value Wb becomes smaller. This is because the smaller the minimum width value Wb, the larger the proportion of light passing outside the ridge portion. Further, in the graph on the left side of the broken line, it can be seen that the closer the structure is to satisfy the relationship of θa <θc and θb <θc, the smaller the ripple becomes. This is because the proportion of light satisfying the conditions of θa <θc and θb <θc, that is, the total reflection condition increases.

As described above, in the semiconductor laser device of Comparative Example 1 that satisfies the relationship of the above equation (3), ripple occurs in the vertical FFP. On the other hand, in the semiconductor laser device of Comparative Example 2 which does not satisfy the relationship of the above formula (3), although ripple is unlikely to occur in the vertical FFP, as described with reference to FIG. 15, the light in the higher order mode is reduced. Is difficult. On the other hand, the semiconductor laser device 1 according to the present embodiment includes a low refractive index unit 70 in order to satisfy the relationship of the above formula (3) and suppress ripple in the vertical FFP.

The action and effect of the low refractive index portion 70 of the semiconductor laser device 1 according to the present embodiment will be described with reference to FIGS. 17 (a) to 17 (c).

FIG. 17A is a top view schematically showing the configuration of the semiconductor laser device 1 according to the embodiment. A graph schematically showing an example of light distribution in the basic mode and the higher-order mode in the X-axis direction is added to the lower side of FIG. 17A.

In the embodiment, as in Comparative Example 1, the light propagates in the Y-axis direction as shown by the broken line arrow. At this time, the light propagating in the ridge portion 40a includes the light of the basic mode and the higher-order mode shown in the lower graph of FIG. 17A. In the embodiment, since the above formula (3) is satisfied as in Comparative Example 1, the light component of the higher-order mode is lost due to the side surface 40b of the ridge portion 40a, and the ratio of the basic mode can be increased.

17 (b) and 17 (c) show the configurations of the semiconductor laser device 1 of the embodiment shown in FIG. 17 (a) when the A31-A32 cross section and the A41-A42 cross section are viewed in the positive Y-axis direction, respectively. It is sectional drawing which shows typically. For convenience, only the substrate 10, the first semiconductor layer 20, the active layer 32, and the second semiconductor layer 40 are shown in FIGS. 17B and 17C.

As shown in FIG. 17B, at a position where the width of the ridge portion 40a is wide, as shown in the light distribution DL3 in the basic mode, the light propagating in the ridge portion 40a is transmitted to the substrate 10 as in Comparative Example 1. It becomes difficult to take.

Further, as shown in FIG. 17C, at a position where the width of the ridge portion 40a is narrow, the low refractive index portion 70 is formed on the outside of the ridge portion 40a, and the light passing outside the ridge portion 40a is low. It passes directly above the refractive index portion 70.

Here, since the low refractive index portion 70 is formed of the silicon oxide film as described above, the refractive index is lower than that of the first semiconductor layer 20. As described above, when the low refractive index portion 70 having a low refractive index is formed below the light passing region (on the side of the first semiconductor layer 20 with respect to the active layer 32), the downward movement of light is restricted. .. That is, the downward movement of the light that propagates outside the ridge portion 40a and reaches directly above the low refractive index portion 70 is suppressed. Therefore, as shown in FIG. 17C, the light distribution DL4 in the basic mode of the laser beam according to the present embodiment is the basic mode of the laser beam in the case where the low refractive index portion 70 is not provided (Comparative Example 1). It will be located above the light distribution DL2. As a result, the light moving to the substrate 10 can be reduced, so that the substrate mode can be reduced. Therefore, according to the semiconductor laser device 1 according to the present embodiment, ripple in the vertical FFP can be suppressed.

<Effect of embodiment>
According to the embodiment, the following effects are achieved.

By setting the angles θa and θb formed by the side surface 40b of the ridge portion 40a and the waveguide direction (Y-axis direction) to be larger than the limit angle θc, the laser beam in the higher-order mode is cut and the laser beam in the basic mode is cut. The ratio of is increased. Further, the low refractive index portion 70 is arranged between the active layer 32 of the light emitting layer 30 and the substrate 10 and at least outside the side surface 40b where the width of the ridge portion 40a is reduced. As a result, as described with reference to FIG. 17 (c), the distribution position of the laser beam propagating in the ridge portion 40a (waveguide WG) is less likely to move downward, so that ripple in the vertical FFP is suppressed. NS. Therefore, it is possible to increase the ratio of the basic mode while suppressing the ripple in the vertical FFP.

The low refractive index portion 70 is formed in the first semiconductor layer 20. As a result, the distribution position of the laser light propagating in the ridge portion 40a (waveguide WG) can be effectively suppressed from moving downward while keeping the distribution position of the laser light in the light emitting layer 30.

The low refractive index portion 70 is arranged along the side surface 40b on the outside of the side surface 40b of the ridge portion 40a in a top view. Specifically, the low refractive index portion 70 is arranged parallel to the side surface 40b at a distance Dd (see FIG. 12) in the width direction. As a result, it is possible to effectively suppress the downward movement of the distribution position of the laser beam propagating in the ridge portion 40a (waveguide WG) by arranging the minimum refractive index portion 70.

The defect density of the light emitting layer 30 arranged directly above the low refractive index portion 70 is higher than the defect density of the light emitting layer 30 other than directly above the low refractive index portion 70. In this case, the interface formed in the light emitting layer 30 directly above the low refractive index portion 70 absorbs unnecessary high-order mode laser light distributed in the vicinity of the light emitting layer 30 directly above the low refractive index portion 70, resulting in higher order. The component of the mode can be reduced.

As shown in FIG. 2, since the cross section of the low refractive index portion 70 has a rectangular shape, the inner end portion and the outer end portion of the low refractive index portion 70 in the X-axis direction are parallel to the Z-axis direction. As a result, an interface is generated in each layer in the vicinity of the position P1 of the inner end portion and the vicinity of the position P2 of the outer end portion. Since an interface is formed in each layer at the positions P1 and P2, the laser light of the higher-order mode can be scattered, so that the component of the higher-order mode can be reduced.

The angles θa and θb formed by the side surface 40b of the ridge portion 40a and the waveguide direction (Y-axis direction) are set to be larger than the limit angle θc. In this case, the limit angle θc is the maximum value of the angle at which the laser beam is totally reflected on the side surface 40b. In this way, the side surface 40b of the ridge portion 40a can reduce the components of the higher-order mode propagating in the ridge portion 40a and increase the ratio of the basic mode.

<Change example>
Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various other modifications can be made.

For example, in the above embodiment, the shape of the low refractive index portion 70 is rectangular in the AA'cross section, but the shape is not limited to this, and other shapes such as a circular shape and an elliptical shape may be used. For example, the shape of the low refractive index portion 70 may be the shape shown in the modified examples 1 and 2 of FIGS. 18 (a) and 18 (b), and the low refractive index portion 70 may be the shape shown in FIGS. 19 (a) and 19 (b). ) May be divided into a plurality of parts as shown in Examples 3 and 4.

In the modified example 1 shown in FIG. 18 (a) and the modified example 2 shown in FIG. 18 (b), the low refractive index portion 70 is configured so that the width in the X-axis direction becomes smaller toward the upper side. Specifically, in the modified example 1 of FIG. 18A, the shape of the low refractive index portion 70 in the AA'cross section is a trapezoidal shape. In the second modification of FIG. 18B, the shape of the low refractive index portion 70 in the AA'cross section is a curved shape. As described above, when the width of the low refractive index portion 70 becomes smaller toward the upper side, the low refractive index portion 70 can be easily formed as compared with the rectangular shape shown in FIG.

In the modified example 3 shown in FIG. 19A, two low refractive index portions 71 arranged in the vertical direction (Z-axis direction) are formed instead of one low refractive index portion 70 as compared with the above embodiment. Will be done. In the modified example 4 shown in FIG. 19B, four low refractive index portions 72 arranged in the width direction (X-axis direction) are formed instead of one low refractive index portion 70 as compared with the above embodiment. Will be done. As shown in FIG. 19B, when a plurality of low refractive index portions 72 are arranged side by side in the width direction outside the ridge portion 40a, the first n-side semiconductor layer 20a (FIG. 5) is formed in the film formation step. Since the portion (see (b)) exposed upward is increased, the crystal growth of the second n-side semiconductor layer 20b (see FIG. 5 (b)) facilitates embedding of the low refractive index portion 70. Further, in the case of FIG. 19B, since a plurality of interfaces are formed directly above the plurality of low refractive index portions 72, the light in the higher-order mode can be further reduced by these interfaces.

Further, in the above embodiment, the layers stacked in the vertical direction are formed parallel to the XY plane, but as shown in the modified example 5 of FIG. 20, each layer arranged directly above the low refractive index portion 70 is formed. , It may be formed so as to be displaced above each layer other than directly above the low refractive index portion 70. In this case, as shown in FIG. 20, each layer above the low refractive index portion 70 is formed while reflecting the shape of the low refractive index portion 70, and each layer above the low refractive index portion 70 has a low refractive index. A step is generated near the position P1 at the inner end of the rate portion 70 and near the position P2 at the outer end. As a result, in the width direction (X-axis direction) of the low refractive index portion 70, between the region directly above the low refractive index portion 70 and the region other than directly above the low refractive index portion 70 (near positions P1 and P2). An interface is created. Therefore, since the laser light of the higher-order mode can be scattered by this interface, the components of the higher-order mode can be reduced.

Further, in the above embodiment, as shown in FIG. 1, the low refractive index portion 70 is arranged outside the side surface 40b where the width of the ridge portion 40a is the minimum value, and the width of the ridge portion 40a is the maximum value. It was not placed on the outside of the side surface 40b. However, the present invention is not limited to this, and as shown in Modification 6 of FIG. 21, the low refractive index portion 70 may be arranged over the entire outside of the side surface 40b of the ridge portion 40a.

In the modified example 6 shown in FIG. 21, the low refractive index portion 70 is arranged on the outside of the side surface 40b at a certain interval from the side surface 40b. The inner end of the low index 70 is parallel to the side surface 40b in response to periodic changes in the width direction of the side surface 40b. The outer end of the low refractive index portion 70 is parallel to the Y-axis direction. In the modified example 6 shown in FIG. 21, the outer end portion of the low refractive index portion 70 may also be parallel to the side surface 40b in response to a periodic change in the width direction of the side surface 40b.

Further, in the above embodiment, as shown in FIG. 1, the side surface 40b is inclined in a direction forming angles θa and θb with respect to the Y-axis direction in the top view, but is oblique as shown in FIG. It is not limited to extending to. For example, as shown in Modification 7 of FIG. 22, the side surface 40b may be composed of a portion parallel to the Y-axis direction and a portion parallel to the X-axis direction.

In the modified example 7 shown in FIG. 22, the portion of the side surface 40b where the width of the ridge portion 40a is the minimum value and the portion of the side surface 40b where the width of the ridge portion 40a is the maximum value are extended in the Y-axis direction and have a width. The portion of the side surface 40b having the minimum value and the portion of the side surface 40b having the maximum width are connected by the portion of the side surface 40b parallel to the X-axis direction. Also in this case, the width of the ridge portion 40a changes periodically according to the position of the ridge portion 40a in the waveguide direction (Y-axis direction). Further, the angle formed by the side surface 40b of the ridge portion 40a and the waveguide direction (Y-axis direction), that is, the angle formed by the portion of the side surface 40b parallel to the X-axis direction and the waveguide direction (Y-axis direction) is limited. Greater than the angle θc. Further, the low refractive index portion 70 has a rectangular shape when viewed from above, and is arranged outside the portion of the side surface 40b where the width of the ridge portion 40a is the minimum value. Therefore, even in the modified example 7, the ratio of the basic mode can be increased while suppressing the ripple in the vertical FFP.

Further, in the above embodiment, the side surface 40b of the ridge portion 40a has a linear shape in the top view, but if the condition of the above formula (3) is satisfied, the side surface 40b has a curved shape in the top view. You may.

Further, in the above embodiment, the low refractive index portion 70 is formed in the first semiconductor layer 20, but the present invention is not limited to this, and the low refractive index portion 70 may be formed in the n-side light guide layer 31 and may be formed in the n-side light guide layer 31. It may be formed so as to straddle the 31 and the first semiconductor layer 20.

Further, in the above embodiment, the low refractive index portion 70 is _{composed of a silicon oxide film (SiO 2} ), but the present invention is not limited to this, and any material having a lower refractive index than that of the first semiconductor layer 20 may be used. In this case as well, it is possible to suppress the occurrence of ripples in the vertical FFP as in the above embodiment. Examples of the material of the low refractive index portion 70 include SiN (refractive index: 2.07), Al ₂ O ₃ (refractive index: 1.79), AlN (refractive index: 2.19), and ITO (refractive index: 2.79). 2.12) and the like. When the low refractive index portion 70 is composed of ITO, the light in the higher order mode can be further suppressed.

Further, in the above embodiment, the semiconductor laser element 1 and the semiconductor laser device 2 may be used not only for processing products but also for other purposes.

In addition, various modifications of the embodiment of the present invention can be made as appropriate within the scope of the technical idea shown in the claims.

1 Semiconductor laser element 10 Substrate 20 First semiconductor layer 30 Light emitting layer 32 Active layer 40 Second semiconductor layer 40a Ridge part 40b Side surface 70, 71, 72 Low refractive index part

Claims (8)

With the board
The first semiconductor layer arranged above the substrate and
A light emitting layer arranged above the first semiconductor layer and
A second semiconductor layer arranged above the light emitting layer and
A low refractive index portion having a refractive index lower than that of the first semiconductor layer is provided.
The second semiconductor layer has a ridge portion for guiding the laser beam generated in the light emitting layer.
The width of the ridge portion changes periodically according to the position of the ridge portion in the waveguide direction.
The angle formed by the side surface of the ridge portion and the waveguide direction is larger than the limit angle defined by the effective refractive index inside the ridge portion and outside the ridge portion.
The low refractive index portion is arranged between the active layer of the light emitting layer and the substrate, and at least outside the side surface where the width of the ridge portion is reduced.
A semiconductor laser device characterized by this. In the semiconductor laser device according to claim 1,
The low refractive index portion is formed in the first semiconductor layer.
A semiconductor laser device characterized by this. In the semiconductor laser device according to claim 1 or 2.
The low refractive index portion is arranged along the side surface on the outside of the side surface of the ridge portion in a top view.
A semiconductor laser device characterized by this. The semiconductor laser device according to any one of claims 1 to 3.
The defect density of the light emitting layer arranged directly above the low refractive index portion is larger than the defect density of the light emitting layer other than directly above the low refractive index portion.
A semiconductor laser device characterized by this. In the semiconductor laser device according to any one of claims 1 to 4.
The low refractive index portion is configured so that the width becomes smaller toward the upper side.
A semiconductor laser device characterized by this. The semiconductor laser device according to any one of claims 1 to 5.
The light emitting layer arranged directly above the low refractive index portion is formed so as to be displaced above the light emitting layer other than directly above the low refractive index portion.
A semiconductor laser device characterized by this. The semiconductor laser device according to any one of claims 1 to 6.
The low refractive index portion is composed of a silicon oxide film.
A semiconductor laser device characterized by this. In the semiconductor laser device according to any one of claims 1 to 7.
The limit angle is the maximum value of the angle at which the laser beam is totally reflected on the side surface.
A semiconductor laser device characterized by this.

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