The present disclosure relates to a semiconductor laser element.
BACKGROUND
Conventionally, a semiconductor laser element that generates laser light in a resonator has been known (see, for example, Patent Literature (PTL) 1). The semiconductor laser element disclosed in PTL 1 includes: a semiconductor stack including an N-type cladding layer, an active layer, a P-type cladding layer, and a P-type contact layer; an insulating film disposed on the semiconductor stack and including an opening portion; and a P-side electrode disposed on the insulating film. The opening portion is formed in the insulating film, and a current is supplied from the P-side electrode to the semiconductor stack via the opening portion. The opening portion is not formed in the vicinity of end faces constituting a resonator of the semiconductor laser element. Accordingly, in the semiconductor laser element disclosed in PTL 1, it is intended to reduce catastrophic optical damage (COD) in the vicinity of the end faces by regulating the supply of a current to the vicinity of the end faces.
PTL 1: International Publication No. WO 2021/206012
However, since the P-type contact layer extends from one end face to the other end face in the semiconductor laser element disclosed in PTL 1, a current can be supplied from the P-side electrode disposed in the opening portion of the insulating film to the vicinity of the end faces via the P-type contact layer. For this reason, COD in the vicinity of the end faces can occur in the semiconductor laser element disclosed in PTL 1.
The present disclosure has been conceived to solve such a problem, and has an object to provide a semiconductor laser element capable of reducing COD in the vicinity of end faces.
In order to solve the above-described problem, a semiconductor laser element according to one aspect of the present disclosure is a semiconductor laser element that emits laser light in a multi-transverse mode, the semiconductor laser element including: a substrate; and a semiconductor stack disposed above the substrate, wherein the semiconductor stack includes: an N-side semiconductor layer disposed above the substrate; an active layer disposed above the N-side semiconductor layer; a P-side semiconductor layer disposed above the active layer; and a P-type contact layer disposed above the P-side semiconductor layer, the semiconductor stack includes two end faces that are opposite to each other, the laser light resonates between the two end faces, the semiconductor stack includes a ridge portion and a bottom portion, the ridge portion extending in a resonance direction of the laser light, the bottom portion being a portion of a top face of the semiconductor stack and surrounding the ridge portion in a top view of the semiconductor stack, the ridge portion protrudes upward from the bottom portion, the ridge portion is spaced apart from the two end faces, the ridge portion includes at least a portion of the P-type contact layer, a current injection window is provided only on the ridge portion out of the top face of the semiconductor stack, the current injection window being a region into which a current is injected, and a distance from a top face of the active layer to the bottom portion is constant.
Moreover, in order to solve the above-described problem, a semiconductor laser element according to one aspect of the present disclosure is a semiconductor laser element that emits laser light in a multi-transverse mode, the semiconductor laser element including: a substrate; and a semiconductor stack disposed above the substrate, wherein the semiconductor stack includes: an N-side semiconductor layer disposed above the substrate; an active layer disposed above the N-side semiconductor layer; a P-side semiconductor layer disposed above the active layer; and a P-type contact layer disposed above the P-side semiconductor layer, the semiconductor stack includes two end faces that are opposite to each other, the laser light resonates between the two end faces, the semiconductor stack includes a ridge portion and a bottom portion, the ridge portion extending in a resonance direction of the laser light, the bottom portion being a portion of a top face of the semiconductor stack and surrounding the ridge portion in a top view of the semiconductor stack, the ridge portion protrudes upward from the bottom portion, the ridge portion is spaced apart from the two end faces, the ridge portion includes at least a portion of the P-type contact layer, a current injection window is provided only on the ridge portion out of the top face of the semiconductor stack, the current injection window being a region into which a current is injected, and the P-type contact layer is exposed in the bottom portion.
The present disclosure provides a semiconductor laser element capable of reducing COD in the vicinity of end faces.
These and other advantages and features will become apparent from the following description thereof taken in conjunction with the accompanying Drawings, by way of non-limiting examples of embodiments disclosed herein.
Hereinafter, embodiments of the present disclosure are described with reference to the drawings. It should be noted that each of the subsequently described embodiments shows a general or a specific example of the present disclosure. Accordingly, the numerical values, shapes, materials, constituent elements, the arrangement and connection of the constituent elements, etc. indicated in the following embodiments are mere examples, and thus are not intended to limit the constituent element.
Moreover, the respective figures are schematic diagrams and are not necessarily accurate illustrations. Accordingly, scales etc. in the respective figures are not necessarily uniform. It should be noted that in the figures, elements that are substantially the same are given the same reference signs, and overlapping description is omitted or simplified.
Furthermore, in the Specification, the terms “above” and “below” do not refer to the upward (vertically upward) and downward (vertically downward) in terms of absolute space. Those terms are defined by relative positional relationships based on a stacking order in a stacked configuration. Additionally, the terms “above” and “below” apply not only when two constituent elements are disposed spaced apart and some other constituent element is interposed between the two constituent elements, but also when two constituent elements are disposed in close proximity to each other such that the two constituent elements are in contact with each other.
A semiconductor laser element according to an embodiment is described below.
An entire configuration of a semiconductor laser element according to the present embodiment is described with reference to
Semiconductor laser element 10 is an element that emits laser light in a multi-transverse mode. As shown in
First end face coating film 71 is disposed on end face 10F, and second end face coating film 72 is disposed on end face 10R. First end face coating film 71 and second end face coating film 72 each are a film for adjusting a laser light reflectivity at a corresponding one of the end faces. In the present embodiment, first end face coating film 71 and second end face coating film 72 each are a multilayer film that includes a dielectric multilayer film. For example, first end face coating film 71 is a multilayer film that includes at least one Al2O3 film and at least one Ta2O5 film, and second end face coating film 72 is a multilayer film that includes at least one Al2O3 film, at least one SiO2 film, and at least one Ta2O5 film. As an example, first end face coating film 71 has a reflectivity of 2%, and second end face coating film 72 has a reflectivity of 95%. It should be noted that each of two end faces of substrate 21 in a resonance direction is on the same plane as a corresponding one of end faces 10F and 10R of semiconductor stack 10S (see
Semiconductor laser element 10 according to the present embodiment emits laser light having a wavelength of at least 900 nm and at most 980 nm. Semiconductor stack 10S of semiconductor laser element 10 includes, for example, a group III-V compound semiconductor comprising an AlGaInAs-based material. Semiconductor laser element 10 emits, for example, laser light in a wavelength range including 976 nm. Moreover, although the details are described later, semiconductor laser element 10 has a window mirror structure. To put it differently, as shown in
As shown in
Substrate 21 is a plate-shaped component that is a base of semiconductor laser element 10. Substrate 21 is a flat plate-shaped component including a principal surface that is uniformly flat. Substrate 21 is a semiconductor substrate such as a GaAs substrate or an insulating substrate such as a sapphire substrate. In the present embodiment, substrate 21 is an N-type GaAs substrate.
Semiconductor stack 10S is a stack disposed above substrate 21. Semiconductor stack 10S includes a plurality of semiconductor layers stacked in the stacking direction (i.e., the Z-axis direction in each figure). In the present embodiment, semiconductor stack 10S includes N-side semiconductor layer 22, active layer 23, P-side semiconductor layer 24, and P-type contact layer 25. As shown in
As shown in
As shown in
Moreover, as shown in
It should be noted that the configuration in which the height of two wing portions 20w from bottom portion 20b is equal to the height of ridge portion 20r from bottom portion 20b includes not only a configuration in which the heights are completely equal but also a configuration in which the heights are substantially equal. For example, a configuration in which the heights have a margin of error of at most 5% is also included in the configuration in which the heights are equal.
Each of two wing portions 20w extends to two end faces 10F and 10R. In the present embodiment, each of two wing portions 20w extends from end face 10F to end face 10R. Accordingly, it is possible to reduce stress applied to ridge portion 20r in the vicinity of end faces 10F and 10R on which stress is readily concentrated when semiconductor laser element 10 is mounted. For this reason, it is possible to prevent ridge portion 20r from being damaged.
The width of bottom portion 20b between ridge portion 20r and wing portion 20w (i.e., a size in the X-axis direction) may be set to at least 5 μm and at most 30 μm. This makes it possible to reduce shear stress outside ridge portion 20r. Since increasing the width of bottom portion 20b excessively causes weight at the time of mounting to be concentrated on ridge portion 20r that becomes a current injection region, the width of bottom portion 20b between ridge portion 20r and wing portion 20w may be set to at least 10 μm and at most 20 μm. Accordingly, it is possible to effectively prevent the rotation of a polarization plane due to the shear stress, and reduce the impact of the shear stress on laser light propagating through an optical waveguide.
Moreover, separation trenches 20t are provided in the both end portions of semiconductor stack 10S in the X-axis direction. Separation trench 20t is a trench used when semiconductor stack 10S is diced.
N-side semiconductor layer 22 is an example of a first semiconductor layer of a first conductivity type disposed above substrate 21 and below active layer 23. Hereinafter, a configuration example of N-side semiconductor layer 22 according to the present embodiment is described with reference to
N-type buffer layer 22a is, for example, an N-type semiconductor layer having a thickness of at most 1.0 μm. By causing the thickness to be small as above, it is possible to prevent an energy shift amount in window region 10w from decreasing due to the impact of the impurities contained in N-type buffer layer 22a when window region 10w is formed by thermal diffusion. In order to increase the energy shift amount in window region 10w, N-type buffer layer 22a may have a thickness of at most 0.5 μm. In the present embodiment, N-type buffer layer 22a is an N-type GaAs layer having a thickness of 0.50 μm.
N-type cladding layer 22c is an N-type semiconductor layer that is disposed above first N-type composition gradient layer 22b and has a refractive index lower than a refractive index of active layer 23. In the present embodiment, N-type cladding layer 22c is an N-type Al0.32Ga0.68As layer having a thickness of 3.00 μm.
First N-type composition gradient layer 22b is a layer that is disposed above N-type buffer layer 22a and whose composition varies in accordance with a position in the stacking direction. Bandgap energy of first N-type composition gradient layer 22b has magnitude between bandgap energy of N-type buffer layer 22a and bandgap energy of N-type cladding layer 22c. The bandgap energy of first N-type composition gradient layer 22b approaches the bandgap energy of N-type cladding layer 22c as the position in the stacking direction approaches N-type cladding layer 22c. The bandgap energy of first N-type composition gradient layer 22b approaches the bandgap energy of N-type buffer layer 22a as the position in the stacking direction approaches N-type buffer layer 22a. Since N-side semiconductor layer 22 includes first N-type composition gradient layer 22b, a rapid change in bandgap energy between N-type buffer layer 22a and N-type cladding layer 22c is mitigated. Accordingly, it is possible to reduce element resistance of semiconductor laser element 10. In the present embodiment, first N-type composition gradient layer 22b is an N-type Alx1Ga1-x1As layer having a thickness of 0.05 μm. Al composition ratio x1 of first N-type composition gradient layer 22b is 0.15 in the vicinity of an interface with N-type buffer layer 22a, is 0.32 in the vicinity of an interface with N-type cladding layer 22c, and increases as the position in the stacking direction approaches N-type cladding layer 22c.
Second N-type composition gradient layer 22d is a layer that is disposed above N-type cladding layer 22c and whose composition varies in accordance with a position in the stacking direction. Bandgap energy of second N-type composition gradient layer 22d has magnitude between bandgap energy of N-type cladding layer 22c and bandgap energy in an end portion (N-type guide layer 23a) below active layer 23. The bandgap energy of second N-type composition gradient layer 22d approaches the bandgap energy of N-type cladding layer 22c as the position in the stacking direction approaches N-type cladding layer 22c. The bandgap energy of second N-type composition gradient layer 22d approaches the bandgap energy in the end portion below active layer 23 as the position in the stacking direction approaches active layer 23. Since N-side semiconductor layer 22 includes second N-type composition gradient layer 22d, a rapid change in bandgap energy between N-type cladding layer 22c and active layer 23 is mitigated. Accordingly, it is possible to reduce element resistance of semiconductor laser element 10. In the present embodiment, second N-type composition gradient layer 22d is an N-type Alx2Ga1-x2As layer having a thickness of 0.03 μm. Al composition ratio x2 of second N-type composition gradient layer 22d is 0.32 in the vicinity of an interface with N-type cladding layer 22c, is 0.285 in the vicinity of an interface with active layer 23, and decreases as the position in the stacking direction approaches active layer 23.
It should be noted that N-side semiconductor layer 22 need not include N-type buffer layer 22a, first N-type composition gradient layer 22b, and second N-type composition gradient layer 22d. Moreover, N-side semiconductor layer 22 may include another semiconductor layer. For example, N-side semiconductor layer 22 may include an undoped semiconductor layer.
Active layer 23 is a light-emitting layer disposed above N-side semiconductor layer 22. In the present embodiment, active layer 23 in a region other than window region 10w has a quantum well structure. Active layer 23 may include a single quantum well or a plurality of quantum wells. Here, active layer 23 in window region 10w is described. Bandgap energy measured based on photoluminescence of a gain region that is a region of active layer 23 other than window region 10w is denoted by Eg1. Bandgap energy measured based on photoluminescence of a region in which window region 10w is provided in active layer 23 is denoted by Eg2. When a difference between Eg1 and Eg2 is denoted by ΔEg, window region is provided to satisfy ΔEg=Eg2−Eg1=100 meV. In other words, the bandgap energy of active layer 23 in window region 10w is greater than the bandgap energy of active layer 23 in the region other than window region 10w (i.e., in the region having the quantum well structure). Since this makes it possible to prevent active layer 23 from absorbing laser light in the vicinity of end faces 10F and 10R of semiconductor stack 10S, it is possible to reduce the occurrence of COD in the vicinity of end faces 10F and 10R.
Moreover, in the case where window region 10w is provided, when bandgap energy measured based on photoluminescence of a boundary region between the gain region and the region in which window region 10w is provided is denoted by Eg3, Eg2>Eg3>Eg1 may be satisfied. Specifically, bandgap energy of active layer 23 in the vicinity of end face 10F and end face 10R may be greater than the bandgap energy measured based on the photoluminescence of the boundary region between the gain region and the region in which window region 10w is provided, and bandgap energy measured based on photoluminescence of a boundary region between a region in which window region 10w is not provided and the region in which window region 10w is provided may be greater than bandgap energy of active layer 23 in a central portion in the resonance direction.
As shown in
Hereinafter, a configuration example of active layer 23 according to the present embodiment is described with reference to
N-type guide layer 23a is a layer disposed above N-side semiconductor layer 22, and has a refractive index higher than a refractive index of N-side semiconductor layer 22. In the present embodiment, N-type guide layer 23a is an N-type Al0.285Ga0.715As layer having a thickness of 1.05 μm. N-type guide layer 23a is doped with silicon as impurities.
Second N-side barrier layer 23b is a layer that is disposed above N-type guide layer 23a and serves as a barrier to a quantum well. Second N-side barrier layer 23b may include a doped region in which impurities are intentionally doped, and an undoped region in which no impurities are doped. In the present embodiment, second N-side barrier layer 23b includes an N-type layer disposed above N-type guide layer 23a, and an undoped layer disposed above the N-type layer. The N-type layer is an N-type Al0.15Ga0.85As layer having a thickness of 0.0268 μm. The N-type layer is doped with silicon as impurities. The undoped layer is an Al0.15Ga0.85As layer having a thickness of 0.0083 μm.
First N-side barrier layer 23c is a layer that is disposed above second N-side barrier layer 23b and serves as a barrier to a quantum well. First N-side barrier layer 23c may include a doped region in which impurities are intentionally doped, and an undoped region in which no impurities are doped. In this case, the undoped region is disposed in a position closer to well layer 23d than the doped region is. The undoped region of first N-side barrier layer 23c has a thickness of, for example, at least 5 nm. Doping a region of first N-side barrier layer 23c in the vicinity of well layer 23d with impurities causes a reduction in series resistance of semiconductor laser element but waveguide loss increases due to the occurrence of free carrier loss. In contrast, increasing the thickness of the undoped region causes an increase in series resistance of semiconductor laser element 10. In order to reduce the increase in free carrier loss while reducing the increase in series resistance of semiconductor laser element 10, the undoped region may have a thickness of at least 5 nm and at most 40 nm. When a doping concentration of the impurities in N-type guide laser 23a gradually increases with distance from well layer 23d, it is possible to reduce the increase in waveguide loss even when the thickness of the undoped region in first N -side barrier layer 23c is set to at least 20 nm. In the present embodiment, first N-side barrier layer 23c is an undoped Al0.50Ga0.32In0.18As layer having a thickness of 0.0018 μm.
Well layer 23d is a layer that is disposed above first N -side barrier layer 23c and serves as a quantum well. Well layer 23d is disposed between first N-side barrier layer 23c and first P-side barrier layer 23e, and are in contact with each of first N-side barrier layer 23c and first P-side barrier layer 23e. Well layer 23d may have a thickness of at least 0.0060 nm. In the present embodiment, well layer 23d is an undoped In0.135Ga0.865As layer having a thickness of 0.0090 μm.
First P-side barrier layer 23e is a layer that is disposed above well layer 23d and serves as a barrier to a quantum well. First P-side barrier layer 23e may include a doped region in which impurities are intentionally doped, and an undoped region in which no impurities are doped. In this case, the undoped region is disposed in a position closer to well layer 23d than the doped region is. The undoped region of first P-side barrier layer 23e has a thickness of, for example, at least 5 nm. Doping a region of first P-side barrier layer 23e in the vicinity of well layer 23d with impurities causes a reduction in series resistance of semiconductor laser element 10, but waveguide loss increases due to the occurrence of free carrier loss. In contrast, increasing the thickness of the undoped region causes an increase in series resistance of semiconductor laser element 10. In order to reduce the increase in free carrier loss while reducing the increase in series resistance of semiconductor laser element 10, the undoped region may have a thickness of at least 5 nm and at most 40 nm. When a doping concentration of the impurities in P-type guide laser 23g gradually increases with distance from well layer 23d, it is possible to reduce the increase in waveguide loss even when the thickness of the undoped region in first P-side barrier layer 23e is set to at least 20 nm. In the present embodiment, first P-side barrier layer 23e is an undoped Al0.50Ga0.32In0.18As layer having a thickness of 0.0018 μm.
Second P-side barrier layer 23f is a layer that is disposed above first P-side barrier layer 23e and serves as a barrier to a quantum well. Second P-side barrier layer 23f may include a doped region in which impurities are intentionally doped, and an undoped region in which no impurities are doped. In the present embodiment, second P-side barrier layer 23f includes an undoped layer disposed above first P-side barrier layer 23e, and a P-type layer disposed above the undoped layer. The undoped layer is an Al0.15Ga0.85As layer having a thickness of 0.0083 μm. The P-type layer is a P-type Al0.15Ga0.85As layer having a thickness of 0.025 μm. The P-type layer is doped with carbon (C) as impurities.
P-type guide layer 23g is a layer disposed above second P-side barrier layer 23f, and has a refractive index higher than a refractive index of P-side semiconductor layer 24. In the present embodiment, P-type guide layer 23g is a P-type Al0.28Ga0.72As layer having a thickness of 0.22 μm. P-type guide layer 23g is doped with carbon as impurities.
P-side semiconductor layer 24 is an example of a second semiconductor layer of a second conductivity type disposed above active layer 23. Hereinafter, a configuration example of P-side semiconductor layer 24 according to the present embodiment is described with reference to
As stated above, P-side semiconductor layer 24 is exposed in bottom portion 20b of semiconductor stack 10S. Second P-type composition gradient layer 24c or P-type cladding layer 24b may be exposed in bottom portion 20b. Bottom portion 20b may be located on the topmost face of second P-type composition gradient layer 24c or may be located between the bottommost and topmost faces of second P-type composition gradient layer 24c. Additionally, bottom portion 20b may be located on the topmost face of P-type cladding layer 24b or may be located between the bottommost and topmost faces of P-type cladding layer 24b.
P-type cladding layer 24b is a P-type semiconductor layer that is disposed above first P-type composition gradient layer 24a and has a refractive index lower than a refractive index of active layer 23. In the present embodiment, P-type cladding layer 24b is a P-type Al0.70Ga0.30As layer having a thickness of 0.75 μm.
First P-type composition gradient layer 24a is a layer that is disposed above active layer 23 and whose composition varies in accordance with a position in the stacking direction. Bandgap energy of first P-type composition gradient layer 24a has magnitude between bandgap energy in an upper end portion (P-type guide layer 23g) of active layer 23 and bandgap energy of P-type cladding layer 24b. The bandgap energy of first P-type composition gradient layer 24a approaches the bandgap energy of P-type cladding layer 24b as the position in the stacking direction approaches P-type cladding layer 24b. The bandgap energy of first P-type composition gradient layer 24a approaches the bandgap energy of the upper end portion of active layer 23 as the position in the stacking direction approaches active layer 23. Since P-side semiconductor layer 24 includes first P-type composition gradient layer 24a, a rapid change in bandgap energy between active layer 23 and P-type cladding layer 24b is mitigated. Accordingly, it is possible to reduce element resistance of semiconductor laser element 10. In the present embodiment, first P-type composition gradient layer 24a is a P-type Aly1Ga1-y1As layer having a thickness of 0.05 μm. Al composition ratio y1 of first P-type composition gradient layer 24a is 0.28 in the vicinity of an interface with active layer 23, is 0.70 in the vicinity of an interface with P-type cladding layer 24b, and increases as the position in the stacking direction approaches P-type cladding layer 24b.
Second P-type composition gradient layer 24c is a layer that is disposed above P-type cladding layer 24b and whose composition varies in accordance with a position in the stacking direction. Bandgap energy of second P-type composition gradient layer 24c has magnitude between bandgap energy of P-type cladding layer 24b and bandgap energy of P-type contact layer 25. The bandgap energy of second P-type composition gradient layer 24c approaches the bandgap energy of P-type cladding layer 24b as the position in the stacking direction approaches P-type cladding layer 24b. The bandgap energy of second P-type composition gradient layer 24c approaches the bandgap energy of P-type contact layer 25 as the position in the stacking direction approaches P-type contact layer 25. Since P-side semiconductor layer 24 includes second P-type composition gradient layer 24c, a rapid change in bandgap energy between P-type cladding layer 24b and P-type contact layer 25 is mitigated. Accordingly, it is possible to reduce element resistance of semiconductor laser element 10. In the present embodiment, second P-type composition gradient layer 24c is a P-type Aly2Ga1-y2As layer having a thickness of 0.05 μm. Al composition ratio y2 of second P-type composition gradient layer 24c is 0.70 in the vicinity of an interface with P-type cladding layer 24b, is 0.15 in the vicinity of an interface with P-type contact layer 25, and decreases as the position in the stacking direction approaches P-type contact layer 25.
P-type contact layer 25 is a layer disposed above P-side semiconductor layer 24. P-type contact layer 25 is disposed below first P-side electrode 41 and is in contact with first P-side electrode 41. P-type contact layer 25 is a P-type semiconductor layer in which impurities are intentionally doped, for example, a P-type GaAs layer. Examples of impurities with which P-type contact layer 25 is doped include carbon. P-type contact layer 25 has a doping concentration of, for example, at least 1.0×1019 cm−3. In the present embodiment, P-type contact layer 25 is a P-type GaAs layer having a thickness of 0.25 μm.
Insulating film 30 is a film having an electrical insulating property disposed above semiconductor stack 10S, and serves as a current blocking film. As shown in
As shown in
Examples of a method of promoting oxidization of bottom portion 20b include a method of performing plasma treatment on bottom portion 20b before insulating film 30 is provided and a method of using chemical solution that promotes oxidization such as compound solution of tartaric acid and hydrogen peroxide solution, in addition to a method of providing, as insulating film 30, a film including oxygen such as SiO2.
First P-side electrode 41 is a P-side electrode in contact with P-type contact layer 25. First P-side electrode 41 is disposed above ridge portion 20r of semiconductor stack 10S, and is in contact with current injection window 25a of P-type contact layer 25 in opening portion 30a of insulating film 30. In the present embodiment, as shown in
Pad electrode 50 is an electrode in a pad shape disposed above first P-side electrode 41. In the present embodiment, each of the both ends of pad electrode 50 in the resonance direction is located between a corresponding one of two end faces 10F and 10R and ridge portion 20r. As stated above, pad electrode 50 is not disposed in two end faces 10F and 10R. Pad electrode 50 includes, for example, an Au film.
Second P-side electrode 42 is a P-side electrode disposed above pad electrode 50. In the present embodiment, second P-side electrode 42 covers pad electrode 50. Second P-side electrode 42 includes, for example, at least one metal from among Pt, Ti, Cr, Ni, Mo, and Au. In the present embodiment, second P-side electrode 42 includes a Ti layer, a Pt layer stacked on the Ti layer, and an Au layer stacked on the Pt layer.
N-side electrode 60 is an electrode disposed on a lower principal surface of substrate 21 (i.e., out of two principal surfaces of substrate 21 that are opposite to each other, a principal surface on which semiconductor stack 10S is not disposed). N-side electrode 60 includes, for example, an AuGe film, a Ni film, an Au film, a Ti film, a Pt film, and an Au film that are stacked in stated order from a substrate 21 side.
In semiconductor laser element 10 having the above-described configuration, a peak position of a light intensity distribution in the stacking direction is located in N-side semiconductor layer 22. For this reason, it is possible to minimize free carrier loss and improve the use efficiency of injected carrier to active layer 23. As a result, it is possible to cause semiconductor laser element 10 to operate with low voltage driving, low threshold current, and high slope efficiency, and it is possible to achieve light output of several tens of watts with high efficiency and low current driving.
Advantageous effects achieved by semiconductor laser element according to the present embodiment are described below. As stated above, semiconductor laser element 10 according to the present embodiment includes semiconductor stack 10S including ridge portion 20r, and bottom portion 20b surrounds ridge portion 20r as shown in
As shown in
By providing bottom portion 20b in a surrounding area of ridge portion 20r in the transverse direction as shown in
As shown in
By providing bottom portion 20b between ridge portion 20r and end faces 10F and 10R as shown in
Moreover, as with bottom portion 20b according to the present embodiment, distance Db from the top face of active layer 23 to bottom portion 20b may be less than the thickness of P-side semiconductor layer 24. In other words, a portion of P-side semiconductor layer 24 may be removed in bottom portion 20b. Accordingly, it is possible to further suppress the current flowing from ridge portion 20r to the vicinity of end faces 10F and 10R.
When distance Db decreases, an effective refractive index difference (Δn) between the outside and inside of ridge portion 20r increases as shown in
When a length of window region 10w in the resonance direction is greater than a length of bottom portion 20b located between end face 10F and ridge portion 20r, window region 10w is also provided directly below ridge portion 20r. Since such window region 10w located directly below ridge portion 20r is located relatively far from end faces 10F and 10R, an effect of reducing the occurrence of COD in end faces 10F and 10R is not large. Additionally, since a relatively large current flows through window region 10w located directly below ridge portion 20r, carrier injection into window region 10w that does not contribute to amplification of laser light increases. For this reason, the length of window region 10w in the resonance direction may be less than the length of bottom portion 20b, located between end face 10F and ridge portion 20r, in the resonance direction. Since this makes it possible to reduce the carrier injection into window region 10w, it is possible to improve the luminous efficiency and the laser optical output. The length of bottom portion 20b, located between end face 10F and ridge portion 20r, in the resonance direction may be at least 80 μm.
The length of window region 10w in the resonance direction may be, for example, at least 70 μm. This makes it possible to reduce thermal load generated when window region 10w is provided, it is possible to reduce the degradation of crystallinity in a region of active layer 23 outside window region 10w.
Moreover, in the present embodiment, as shown in
In addition, by bringing the ends of pad electrode 50 in the resonance direction close to end faces 10F and 10R, it is possible to improve heat dissipation of end faces 10F and 10R. This makes it possible to reduce deterioration resulting from heat of semiconductor laser element 10. A space between each of the ends of pad electrode 50 in the resonance direction and a corresponding one of end faces 10F and 10R may be at most 15 μm. This makes it possible to further improve the heat dissipation.
A method of manufacturing semiconductor laser element 10 according to the present embodiment is described with reference to
First, as shown in
In the present embodiment, N-side semiconductor layer 22, active layer 23, P-side semiconductor layer 24, and P-type contact layer 25 are stacked on substrate 21 that is an N-type GaAs wafer by growing crystals sequentially using a crystal growth technique based on metalorganic chemical vapor deposition (MOCVD).
N-type buffer layer 22a, first N-type composition gradient layer 22b, N-type cladding layer 22c, and second N-type composition gradient layer 22d are sequentially crystal-grown as N-side semiconductor layer 22 on substrate 21.
N-type guide layer 23a, second N-side barrier layer 23b, first N-side barrier layer 23c, well layer 23d, first P-side barrier layer 23e, second P-side barrier layer 23f, and P-type guide layer 23g are sequentially crystal-grown as active layer 23 on N-side semiconductor layer 22.
First P-type composition gradient layer 24a, P-type cladding layer 24b, and second P-type composition gradient layer 24c are sequentially crystal-grown as P-side semiconductor layer 24 on active layer 23.
Next, as shown in
In the vacancy diffusion method, it is possible to provide window region 10w by performing rapid high-temperature processing on semiconductor stack 10S. For example, by providing a protective film that generates Ga vacancies at the time of high-temperature processing on semiconductor stack 10S in a region in which a window region is provided and then diffusing Ga vacancies by exposing the protective film to extremely high-temperature heat in a range of at least 750° C. and at most 950° C. that is close to a crystal growth temperature, it is possible to disorder the quantum well structure of active layer 23 by interdiffusion of vacancies and group III elements, to achieve a window structure(transparency). As a result, it is possible to increase a band gap of active layer 23 and to cause the region whose quantum well structure is disordered to serve as window region 10w. Additionally, in a region other than window region 10w, it is possible to prevent the quantum well structure from being disordered, by providing a protective film that reduces generation of Ga vacancies at the time of high-temperature processing. It should be noted that although window region 10w is provided by the vacancy diffusion method in the present embodiment, window region 10w may be provided by another method such as the impurity diffusion method.
Then, as shown in
Next, as shown in
It should be noted that it is possible to use, for example, a sulfuric-acid-based etching solution as an etching solution when separation trench 20t is provided. In this case, it is possible to use an etching solution having a ratio of sulfuric acid to hydrogen peroxide solution to water=1:1:10. In addition, an etching solution is not limited to the sulfuric-acid-based etching solution, and may be an organic-acid-based etching solution or an ammonia-based etching solution.
Moreover, separation trench 20t is provided by isotropic wet etching. Accordingly, it is possible to create a constricted structure (i.e., an overhung structure) in a plurality of semiconductor layers by forming an inclined surface on the lateral faces of the plurality of semiconductor layers. An inclination angle of the lateral face of separation trench 20t differs according to an Al composition ratio of an AlGaAs material of each of the plurality of semiconductor layers. It is possible to increase an etching rate by increasing the Al composition ratio of the AlGaAs material. For this reason, in order to form a lateral face having an inclination as shown in
Then, after the mask for separation trench 20t is removed by a hydrofluoric-acid-based etching solution, a SiN film is deposited as insulating film 30 on the entire surface above substrate 21 as shown in
It is possible to use, as etching of insulating film 30, wet etching using a hydrofluoric-acid-based etching solution or dry etching such as reactive ion etching (RIE). Moreover, although insulating film 30 is a SiN film, the present embodiment is not limited to this example. Insulating film 30 may be, for example, a SiO2 film. Here, a technique for providing insulating film 30 that can be employed in the present embodiment may be plasma chemical vapor deposition (hereinafter PCVD). Furthermore, it is possible to use, as source gas for forming insulating film 30, mixed gas of SiH4, CF4, NH3, N2O, N2, and the like.
In the present embodiment, a film formation technique is a PCVD method, and mixed gas of SiH4, NH3, and N2 is used as source gas. Although it is possible to set, as film formation conditions, a SiH4 volume content rate in mixed gas to at least 5% and at most 18%, a temperature of a lower electrode on which a semiconductor substrate is disposed to at least 150° C. and at most 350° C., an intra-chamber pressure to at least 50 Pa and at most 200 Pa, and a RF power to at least 100 W and at most 400 W, the present embodiment is not limited to this example. Film formation conditions may be selected appropriately.
It should be noted that since source gas includes no O2 when a SiN film is used as insulating film 30, the surface of bottom portion is less easily oxidized. When a SiO2 film is used as insulating film 30, mixed gas of SiH4, N2O, and N2 is used as source gas.
After that, as shown in
Specifically, first P-side electrode 41 including a stacked film of a Ti film, a Pt film, and an Au film is provided as a base electrode by an electron beam evaporation method. Subsequently, pad electrode including an Au plated film is provided by an electrolytic plating method. Afterward, pad electrode 50 in the vicinity of end faces is selectively removed using the photolithography technique or the etching technique and a lift-off technique. It should be noted that it is possible to use an iodine solution as an etching solution for etching pad electrode 50 including the Au plated film. Subsequent to that, second P-side electrode 42 including a stacked film of a Ti film, a Pt film, and an Au film is provided on pad electrode 50 by the electron beam evaporation method. As stated above, although first P-side electrode 41 and second P-side electrode 42 are provided over the almost entire length in the resonance direction, pad electrode 50 is not provided in the vicinity of end faces 10F and 10R.
Next, as shown in
Then, though not shown, substrate 21 on which semiconductor stack 10S is provided is separated into bars by, for example, dicing using a blade or cleaving, and chip separation is subsequently performed by further cutting separation trench 20t as a cutting portion. As a result, it is possible to manufacture diced semiconductor laser element 10.
A semiconductor laser element according to each of Variation 1 to Variation 8 is described below. Although a semiconductor laser element according to each of Variation 1 to Variation 3 includes a semiconductor stack similar to semiconductor stack 10S of semiconductor laser element 10 according to the embodiment, the semiconductor laser element differs from semiconductor laser element 10 in part of the layer configuration of semiconductor stack 10S. A semiconductor laser element according to each of Variation 4 to Variation 8 differs from semiconductor laser element 10 according to the embodiment in the configurations of ridge portion 20r, wing portion 20w, and bottom portion 20b of semiconductor stack 10S. Hereinafter, among the configurations of the semiconductor laser elements according to Variation 1 to Variation 8, configurations different from the configuration of semiconductor laser element 10 according to the embodiment are mainly described.
A configuration of a semiconductor laser element according to Variation 1 is described below.
First N-type composition gradient layer 22b of the semiconductor laser element according to Variation 1 is an N-type Alx1Ga1-x1As layer having a thickness of 0.05 μm. Al composition ratio x1 of first N-type composition gradient layer 22b is 0.15 in the vicinity of an interface with N-type buffer layer 22a, is 0.353 in the vicinity of an interface with N-type cladding layer 22c, and increases as the position in the stacking direction approaches N-type cladding layer 22c.
N-type cladding layer 22c of the semiconductor laser element according to Variation 1 is an N-type Al0.353Ga0.647As layer having a thickness of 2.40 μm.
Second N-type composition gradient layer 22d of the semiconductor laser element according to Variation 1 is an N-type Alx2Ga1-x2As layer having a thickness of 0.03 μm. Al composition ratio x2 of second N-type composition gradient layer 22d is 0.353 in the vicinity of an interface with N-type cladding layer 22c, is 0.323 in the vicinity of an interface with active layer 23, and decreases as the position in the stacking direction approaches active layer 23.
N-type guide layer 23a of the semiconductor laser element according to Variation 1 is an N-type Al0.323Ga0.677As layer having a thickness of 0.95 μm.
Second N-side barrier layer 23b of the semiconductor laser element according to Variation 1 includes an N-type layer disposed above N-type guide layer 23a, and an undoped layer disposed above the N-type layer. The N-type layer is an N-type Al0.18Ga0.82As layer having a thickness of 0.0250 μm. The N-type layer is doped with silicon as impurities. The undoped layer is an Al0.18Ga0.82As layer having a thickness of 0.0065 μm.
First N-side barrier layer 23c of the semiconductor laser element according to Variation 1 is an undoped Al0.35Ga0.55In0.10As layer having a thickness of 0.0035 μm.
Well layer 23d of the semiconductor laser element according to Variation 1 is an undoped In0.11Ga0.89As layer having a thickness of 0.0060 μm. First P-side barrier layer 23e of the semiconductor laser element according to Variation 1 is an undoped Al0.35Ga0.55In0.10As layer having a thickness of 0.0035 μm.
Second P-side barrier layer 23f of the semiconductor laser element according to Variation 1 includes an undoped layer disposed above first P-side barrier layer 23e, and a P-type layer disposed above the undoped layer. The undoped layer is an Al0.18Ga0.82As layer having a thickness of 0.0065 μm. The P-type layer is a P-type Al0.18Ga0.82As layer having a thickness of 0.025 μm. The P-type layer is doped with carbon (C) as impurities.
P-type guide layer 23g of the semiconductor laser element according to Variation 1 is a P-type Al0.32Ga0.68As layer having a thickness of 0.1825 μm.
First P-type composition gradient layer 24a of the semiconductor laser element according to Variation 1 is a P-type Aly1Ga1-y1As layer having a thickness of 0.05 μm. Al composition ratio y1 of first P-type composition gradient layer 24a is 0.32 in the vicinity of an interface with active layer 23, is 0.70 in the vicinity of an interface with P-type cladding layer 24b, and increases as the position in the stacking direction approaches P-type cladding layer 24b.
The semiconductor laser element according to Variation 1 having the above configuration achieves the same advantageous effects as semiconductor laser element 10 according to the embodiment. The semiconductor laser element according to Variation 1 is capable of emitting laser light in a wavelength range including 915 nm.
A configuration of a semiconductor laser element according to Variation 2 is described below.
N-type buffer layer 22a of the semiconductor laser element according to Variation 2 is an N-type GaAs layer having a thickness of 0.01 μm.
First N-type composition gradient layer 22b of the semiconductor laser element according to Variation 2 is an N-type Alx1Ga1-x1As layer having a thickness of 0.05 μm. Al composition ratio x1 of first N-type composition gradient layer 22b is 0.15 in the vicinity of an interface with N-type buffer layer 22a, is 0.25 in the vicinity of an interface with N-type cladding layer 22c, and increases as the position in the stacking direction approaches N-type cladding layer 22c.
N-type cladding layer 22c of the semiconductor laser element according to Variation 2 is an N-type Al0.25Ga0.75As layer having a thickness of 1.80 μm.
N-side semiconductor layer 22 of the semiconductor laser element according to Variation 2 does not include second N-type composition gradient layer 22d. In contrast, N-type guide layer 23a in active layer 23 of the semiconductor laser element according to Variation 2 includes: a third N-type guide layer; a second N-type guide layer disposed above the third N-type guide layer; and a first N-type guide layer disposed above the second N-type guide layer. The third N-type guide layer is an N-type Al0.25Ga0.75As layer having a thickness of 0.20 μm. The second N-type guide layer is an N-type Al0.23Ga0.77As layer having a thickness of 0.60 μm. The first N-type guide layer is an N-type Al0.21Ga0.79As layer having a thickness of 0.46 μm.
Second N-side barrier layer 23b of the semiconductor laser element according to Variation 2 includes an N-type layer disposed above N-type guide layer 23a, and an undoped layer disposed above the N-type layer. The N-type layer is an N-type Al0.16Ga0.84As layer having a thickness of 0.0268 μm. The N-type layer is doped with silicon as impurities. The undoped layer is an Al0.16Ga0.84As layer having a thickness of 0.0083 μm.
Second P-side barrier layer 23f of the semiconductor laser element according to Variation 2 is an Al0..16Ga0.84As layer having a thickness of 0.0083 μm.
P-type guide layer 23g of the semiconductor laser element according to Variation 2 is a P-type Alz1Ga1-z1As layer having a thickness of 0.29 μm. Al composition ratio z1 of P-type guide layer 23g is 0.19 in the vicinity of an interface with second P-side barrier layer 23f, is 0.21 in the vicinity of an interface with P-side semiconductor layer 24, and increases as the position in the stacking direction approaches P-side semiconductor layer 24.
First P-type composition gradient layer 24a of the semiconductor laser element according to Variation 2 is a P-type Aly1Ga1-y1As layer having a thickness of 0.05 μm. Al composition ratio y1 of first P-type composition gradient layer 24a is 0.21 in the vicinity of an interface with active layer 23, is 0.70 in the vicinity of an interface with P-type cladding layer 24b, and increases as the position in the stacking direction approaches P-type cladding layer 24b.
P-type cladding layer 24b of the semiconductor laser element according to Variation 2 is a P-type Al0.70Ga0.30As layer having a thickness of 0.70 μm.
The semiconductor laser element according to Variation 2 having the above configuration achieves the same advantageous effects as semiconductor laser element 10 according to the embodiment.
A configuration of a semiconductor laser element according to Variation 3 is described below.
N-type buffer layer 22a of the semiconductor laser element according to Variation 3 is an N-type GaAs layer having a thickness of 0.10 μm.
First N-type composition gradient layer 22b of the semiconductor laser element according to Variation 3 is an N-type Alx1Ga1-x1As layer having a thickness of 0.05 μm. Al composition ratio x1 of first N-type composition gradient layer 22b is 0.15 in the vicinity of an interface with N-type buffer layer 22a, is 0.24 in the vicinity of an interface with N-type cladding layer 22c, and increases as the position in the stacking direction approaches N-type cladding layer 22c.
N-type cladding layer 22c of the semiconductor laser element according to Variation 3 is an N-type Al0.24Ga0.76As layer having a thickness of 1.80 μm.
Second N-type composition gradient layer 22d of the semiconductor laser element according to Variation 3 is an N-type Alx2Ga1-x2As layer having a thickness of 1.00 μm. Al composition ratio x2 of second N-type composition gradient layer 22d is 0.24 in the vicinity of an interface with N-type cladding layer 22c, is 0.22 in the vicinity of an interface with active layer 23, and decreases as the position in the stacking direction approaches active layer 23.
N-type guide layer 23a of the semiconductor laser element according to Variation 3 includes a second N-type guide layer and a first N-type guide layer that is disposed above the second N-type guide layer. The second N-type guide layer is an N-type Alz2Ga1-z2As layer having a thickness of 0.40 μm. Al composition ratio z2 of the second N-type guide layer is 0.22 in the vicinity of an interface with N-side semiconductor layer 22, is 0.19 in the vicinity of an interface with the first N-type guide layer, and decreases as the position in the stacking direction approaches the first N-type guide layer. The first N-type guide layer is an N-type Al0.19Ga0.81As layer having a thickness of 0.09 μm.
Second N-side barrier layer 23b of the semiconductor laser element according to Variation 3 includes an N-type layer disposed above N-type guide layer 23a, and an undoped layer disposed above the N-type layer. The N-type layer is an N-type Al0.16Ga0.84As layer having a thickness of 0.0268 μm. The N-type layer is doped with silicon as impurities. The undoped layer is an Al0.16Ga0.84As layer having a thickness of 0.0083 μm.
Second P-side barrier layer 23f of the semiconductor laser element according to Variation 3 is an Al0.16Ga0.84As layer having a thickness of 0.0083 μm.
P-type guide layer 23g of the semiconductor laser element according to Variation 3 includes a first P-type guide layer and a second P-type guide layer that is disposed above the first P-type guide layer. The first P-type guide layer is a P-type Al0.19Ga0.81As layer having a thickness of 0.01 μm. The second P-type guide layer is a P-type Alz1Ga1-z1As layer having a thickness of 0.28 μm. Al composition ratio z1 of the second P-type guide layer is 0.19 in the vicinity of an interface with the first P-side guide layer, is 0.21 in the vicinity of an interface with P-side semiconductor layer 24, and increases as the position in the stacking direction approaches P-side semiconductor layer 24.
First P-type composition gradient layer 24a of the semiconductor laser element according to Variation 3 is a P-type Aly1Ga1-y1As layer having a thickness of 0.05 μm. Al composition ratio y1 of first P-type composition gradient layer 24a is 0.21 in the vicinity of an interface with active layer 23, is 0.70 in the vicinity of an interface with P-type cladding layer 24b, and increases as the position in the stacking direction approaches P-type cladding layer 24b.
P-type cladding layer 24b of the semiconductor laser element according to Variation 3 is a P-type Al0.70Ga0.30As layer having a thickness of 0.70 μm. The semiconductor laser element according to Variation 3 having the above configuration achieves the same advantageous effects as semiconductor laser element 10 according to the embodiment.
A semiconductor laser element according to Variation 4 is described below with reference to
Semiconductor laser element 110 according to Variation 4 having the above configuration achieves the same advantageous effects as semiconductor laser element 10 according to the embodiment, except for the advantageous effect achieved by wing portions 20w.
A semiconductor laser element according to Variation 5 is described below with reference to
Semiconductor laser element 210 according to Variation 5 having the above configuration achieves the same advantageous effects as semiconductor laser element 10 according to the embodiment. In addition, since bottom portions 20b are disposed on both sides of wing portion 20w in the transverse direction, semiconductor laser element 210 according to Variation 5 is capable of improving adhesiveness of insulating film 30 to semiconductor stack 10S.
A semiconductor laser element according to Variation 6 is described below with reference to
Semiconductor laser element 310 according to Variation 6 having the above configuration achieves the same advantageous effects as semiconductor laser element 10 according to the embodiment. In addition, since bottom portion 20b is disposed around wing portion 20w, semiconductor laser element 310 according to Variation 6 is capable of improving adhesiveness of insulating film 30 to semiconductor stack 10S.
A semiconductor laser element according to Variation 7 is described below with reference to
Semiconductor laser element 410 according to Variation 7 having the above configuration achieves the same advantageous effects as semiconductor laser element 10 according to the embodiment. Moreover, since, for example, by semiconductor laser element 410 according to Variation 7 including dummy ridge portion 420r, stress applied to semiconductor laser element 410 is dispersed to dummy ridge portion 420r when semiconductor laser element 410 is mounted, it is possible to prevent the stress from being concentrated only on ridge portion 20r. For this reason, it is possible to prevent ridge portion 20r from being damaged. Furthermore, since adhesiveness between insulating film 30 and bottom portion 20b is poor when an AlGaAs layer is exposed in bottom portion 20b, insulating film 30 is likely to come off easily in a region in which insulating film 30 is in contact with bottom portion 20b. Since semiconductor laser element 410 according to Variation 7 makes it possible to replace a portion of a region that is between end faces 10F and 10R and ridge portion 20r and to which an AlGaAs layer is exposed with dummy ridge portion 420r including GaAs, semiconductor laser element 410 is capable of improving adhesiveness between insulating film 30 and semiconductor stack 10S.
A semiconductor laser element according to Variation 8 is described below with reference to
As shown in
Semiconductor laser element 510 according to Variation 8 having the above configuration achieves the same advantageous effects as semiconductor laser element 10 according to the embodiment. Moreover, since, for example, by semiconductor laser element 510 according to Variation 8 including dummy ridge portion 520r, stress applied to semiconductor laser element 510 is dispersed to dummy ridge portion 520r when semiconductor laser element 510 is mounted, it is possible to prevent the stress from being concentrated only on ridge portion 20r. For this reason, it is possible to prevent ridge portion 20r from being damaged. Furthermore, since adhesiveness between insulating film 30 and bottom portion 20b is poor when an AlGaAs layer is exposed in bottom portion 20b, insulating film 30 is likely to come off easily in a region in which insulating film 30 is in contact with bottom portion 20b. Since semiconductor laser element 510 according to Variation 8 makes it possible to replace a portion of a region that is between each of end faces 10F and 10R and ridge portion 20r and to which an AlGaAs layer is exposed with dummy ridge portion 520r including GaAs, semiconductor laser element 510 is capable of improving adhesiveness between insulating film 30 and semiconductor stack 10S. Moreover, in semiconductor laser element 510 according to Variation 8, since bottom portion 20b is not in contact with end faces 10F and 10R, an adhesion surface between insulating film 30 and bottom portion 20b having poor adhesiveness is not exposed from each of end faces 10F and 10R. Accordingly, it is possible to further prevent insulating film 30 from coming off.
Although the semiconductor laser element according to the present disclosure has been described based on each of the embodiments, the present disclosure is not limited to the embodiment.
For example, in Variation 1 to Variation 8, distance Db of bottom portion 20b from the top face of active layer 23 may be greater than or equal to the thickness of P-side semiconductor layer 24 or may be less than the thickness of P-side semiconductor layer 24. In other words, P-type contact layer 25 may be exposed in bottom portion 20b, and P-side semiconductor layer 24 may be exposed in bottom portion 20b.
Moreover, forms obtained by various modifications to the respective embodiments that can be conceived by a person skilled in the art as well as forms achieved by arbitrarily combining the constituent elements and functions in the respective embodiments are included in the scope of the present disclosure as long as they do not depart from the essence of the present disclosure.
The semiconductor laser element etc. according to the present disclosure is applicable as a highly efficient light source to, for example, a light source for processing machine.
This is a continuation application of PCT International Application No. PCT/JP2021/047705 filed on Dec. 22, 2021, designating the United States of America, which is based on and claims priority of U.S. Provisional Patent Application No. 63/143,463 filed on Jan. 29, 2021. The entire disclosures of the above-identified applications, including the specifications, drawings and claims are incorporated herein by reference in their entirety.
Number | Date | Country | |
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63143463 | Jan 2021 | US |
Number | Date | Country | |
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Parent | PCT/JP2021/047705 | Dec 2021 | US |
Child | 18358610 | US |