Laser Diode

Abstract

To provide a laser diode of low element resistance.SOLUTION: A laser diode comprises an Al containing nitride semiconductor substrate, and a semiconductor laminate part disposed on the nitride semiconductor substrate. The semiconductor laminate part includes: a first conductivity type clad layer disposed on the nitride semiconductor substrate and including a nitride semiconductor layer of a first conductivity type; a light-emitting layer disposed on the first conductivity type clad layer and formed from a nitride semiconductor including one or more quantum wells; and a second conductivity type clad layer disposed on the light-emitting layer and including a nitride semiconductor of a second conductivity type. At least a portion of the semiconductor laminate part is a mesa structure formed for light resonance and emission and in side faces of the mesa structure, and a side face which is not vertical to a light resonance direction includes a plurality of projections in planar view.SELECTED DRAWING: Figure 1A

Description

[Technical Field]

[0001] The present disclosure relates to laser diodes. [Background technology]

[0002] Nitride semiconductors are suitable as materials for laser diodes because they have a direct transition recombination mode, which allows them to obtain high recombination efficiency and high optical gain. For example, a technology has been disclosed for oscillating a current-injection type laser diode in the ultraviolet region using nitride semiconductors (e.g., Non-Patent Document 1).

[0003] Taking into consideration common technical knowledge about laser diodes, it is preferable that a laser diode that emits ultraviolet light be configured to oscillate at a low oscillation threshold current density. Furthermore, in order to prevent deterioration of element performance due to heat, it is preferable that a laser diode that emits ultraviolet light has oscillation characteristics with lower driving power by reducing element resistance. To reduce element resistance and enable the laser diode to oscillate at low power, it is considered appropriate to configure the electrodes arranged on the mesa structure as close as possible to the side surfaces of the mesa structure. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Zhang et al., Applied Physics Express 12, 124003(2019) Summary of the Invention [Problem to be solved by the invention]

[0005] However, even if such a configuration is applied to a laser diode that emits ultraviolet light, the desired low oscillation threshold current density cannot be obtained. The reason for this is thought to be that near the side surface of the mesa structure, dislocations introduced from the side surface of the mesa structure reach the light-emitting layer directly below the electrode provided on the mesa structure, resulting in the formation of a non-light-emitting region that inhibits optical gain. In view of the above circumstances, an object of the present disclosure is to provide a laser diode that achieves a lower element resistance. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems, a laser diode according to one embodiment of the present disclosure includes a nitride semiconductor substrate containing Al, and a semiconductor laminate portion disposed on the nitride semiconductor substrate, wherein the semiconductor laminate portion has: a first-conductivity-type cladding layer including a nitride semiconductor layer of a first conductivity type disposed on the nitride semiconductor substrate; an emission layer formed of a nitride semiconductor including one or more quantum wells disposed on the first-conductivity-type cladding layer; and a second-conductivity-type cladding layer including a nitride semiconductor of a second conductivity type disposed on the emission layer, at least a portion of the semiconductor laminate portion is a mesa structure formed for optical resonance and emission, and the side surfaces of the mesa structure that are not perpendicular to the optical resonance direction have multiple protrusions in a planar view. It should be noted that the above summary of the invention does not list all of the features of the present disclosure. [Effects of the Invention]

[0007] According to one aspect of the present disclosure, a laser diode with a low oscillation threshold current can be provided. [Brief explanation of the drawings]

[0008] [Figure 1A] FIG. 1 is a schematic plan view illustrating an example of a configuration of a laser diode according to an embodiment of the present disclosure. [Figure 1B] 1 is a cross-sectional view schematically illustrating a configuration example of a laser diode according to an embodiment of the present disclosure. [Figure 2A]3 is a cross-sectional view schematically illustrating a configuration example of a protrusion of a laser diode according to an embodiment of the present disclosure. FIG. [Figure 2B] 3 is a cross-sectional view schematically illustrating a configuration example of a protrusion of a laser diode according to an embodiment of the present disclosure. FIG. [Figure 2C] 3 is a cross-sectional view schematically illustrating a configuration example of a protrusion of a laser diode according to an embodiment of the present disclosure. FIG. [Figure 3] FIG. 10 is a cross-sectional view schematically illustrating another configuration example of a laser diode according to an embodiment of the present disclosure. [Figure 4] FIG. 10 is a cross-sectional view schematically illustrating another configuration example of a laser diode according to an embodiment of the present disclosure. [Figure 5] FIG. 10 is a cross-sectional view schematically illustrating another configuration example of a laser diode according to an embodiment of the present disclosure. [Figure 6] FIG. 10 is a cross-sectional view schematically illustrating another configuration example of a laser diode according to an embodiment of the present disclosure. [Figure 7] FIG. 10 is a cross-sectional view schematically illustrating another configuration example of a laser diode according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0009] The laser diode according to the present disclosure will be described below through embodiments, but the following embodiments do not limit the scope of the invention according to the claims. Also, not all of the combinations of features described in the embodiments are necessarily essential to the solution of the invention.

[0010] For the sake of convenience, "upper" will refer to the second electrode side depicted in the drawings, and "lower" will refer to the substrate side depicted in the drawings. However, "upper" and "lower" are merely defined for convenience and should not be interpreted restrictively.

[0011] 1. Embodiment A laser diode according to an embodiment of the present disclosure will be described.

[0012] (1.1) Structure of ultraviolet laser diode The laser diode according to the present disclosure comprises: The semiconductor laminate comprises a nitride semiconductor substrate containing Al, and a semiconductor laminate portion disposed on the nitride semiconductor substrate, the semiconductor laminate portion having: a first conductivity type cladding layer disposed on the nitride semiconductor substrate and including a nitride semiconductor layer of a first conductivity type; a light emitting layer formed of a nitride semiconductor including one or more quantum wells and disposed on the first conductivity type cladding layer; and a second conductivity type cladding layer disposed on the light emitting layer and including a nitride semiconductor of a second conductivity type, at least a portion of the semiconductor laminate portion is a mesa structure formed for optical resonance and emission, and the side surfaces of the mesa structure that are not perpendicular to the optical resonance direction have a plurality of protrusions in a planar view.

[0013] The reason why the laser diode according to the present disclosure can achieve low element resistance is believed to be that the laser diode has multiple convex portions on the sides of the mesa structure that are not perpendicular to the optical resonance direction (sides that are not the resonator mirror end faces), which suppresses dislocations introduced from the sides of the mesa structure and reduces non-light-emitting regions that inhibit optical gain compared to a configuration that does not have such convex portions. Each component of the ultraviolet laser diode according to the present disclosure will be described below.

[0014] <Nitride semiconductor substrate> The nitride semiconductor substrate (hereinafter sometimes referred to as substrate) contains a nitride semiconductor containing Al. The nitride semiconductor containing Al is, for example, AlN. That is, the substrate is preferably an AlN single crystal substrate. Furthermore, the nitride semiconductor containing Al is not limited to AlN, and may be, for example, AlGaN. For example, when the substrate is a nitride semiconductor single crystal substrate such as AlN or AlGaN, the difference in lattice constant with the nitride semiconductor layer formed on the substrate becomes small, and threading dislocations can be reduced by growing the nitride semiconductor layer in a lattice-matched system. The threading dislocation density of the substrate is 5×10 4 cm -2 In particular, from the viewpoint of reducing the oscillation threshold current, the threading dislocation density is preferably 1×10 3 More than 1×10 4 cm -2 More preferably, it is:

[0015] Here, the "comprises" in the expression "comprises a nitride semiconductor" means that the layer mainly contains a nitride semiconductor, but this expression also includes cases where other elements are included. Specifically, this expression also includes cases where the composition of this layer is slightly modified by adding a small amount of an element other than the nitride semiconductor (for example, a few percent or less of an element such as Ga (when Ga is not the main element), In, As, P, or Sb). The wording "comprises" has a similar meaning when describing the composition of other layers. Furthermore, the small amount of elements contained is not limited to the above.

[0016] The substrate may be doped n-type or p-type with donor or acceptor impurities, or may be a mixed crystal of a nitride semiconductor such as AlN and sapphire (Al2O3), Si, SiC, MgO, Ga2O3, ZnO, GaN, or InN.

[0017] For example, the substrate preferably has a layer thickness of 100 μm or more and 600 μm or less. The crystal plane orientation may be c-plane (0001), a-plane (11-20), or m-plane (10-10), with a c-plane (0001) being more preferred. Furthermore, the crystal may be formed on a plane tilted at some angle (for example, -4° to 4°, preferably -0.4° to 0.4°) from the normal to the c-plane (0001), but is not limited thereto.

[0018] <First conductivity type cladding layer> The first-conductivity-type clad layer is formed on a substrate. Here, for example, in the expression "The first-conductivity-type clad layer is formed on a substrate", the word "on" means that the first-conductivity-type clad layer is formed on one surface of the substrate. Also, when there is another layer further between the substrate and the first-conductivity-type clad layer, it is included in the above expression. In the relationship between other layers as well, the word "above" has the same meaning. For example, when the second-conductivity-type clad layer is formed via an electron blocking layer on the first-conductivity-type waveguide layer described later, it is included in the expression "The second-conductivity-type clad layer is formed on the first-conductivity-type waveguide layer". Also, in the description of this embodiment, "the first conductivity type" and "the second conductivity type" each mean semiconductors showing different conductivity types. For example, when one is n-type conductivity, the other is p-type conductivity.

[0019] The first-conductivity-type clad layer in the laser diode of this embodiment is a layer of a nitride semiconductor containing Al and Ga. The first-conductivity-type clad layer is, for example, Al a Ga (1-a) formed by N (0 < a < 1). Thereby, when forming a material corresponding to the bandgap energy in the deep ultraviolet region as a light-emitting layer, it becomes possible to enhance the crystallinity of the light-emitting layer and improve the light-emitting efficiency. From the viewpoint of realizing high light-emitting efficiency, the nitride semiconductor constituting the first-conductivity-type clad layer is preferably a mixed crystal of AlN and GaN. Also, from the viewpoint of growing with complete strain with respect to the substrate, the first-conductivity-type clad layer is more preferably formed by Al a Ga N (0.6 ≤ a ≤ 0.8).

[0020] The first-conductivity-type clad layer may be doped with an impurity. Examples of the impurity include Si, Ge, C, O, etc. As the impurity, any one of these impurities may be selected, or a plurality of these impurities may be selected. The concentration of the impurity is not particularly limited, but is 1 × 10 17 cm -3 or more and 1 × 10 20 cm -3 ​Preferably, it is 5 x 10 or less. 18 cm -3 5x10 or more 19 cm -3 More preferably, it is:

[0021] From the viewpoints of lattice relaxation within the first conductivity type cladding layer and film resistance, the first conductivity type cladding layer preferably has a layer thickness of 200 nm or more and 800 nm or less, more preferably 300 nm or more and 750 nm or less, and even more preferably 300 nm or more and 500 nm or less.

[0022] <Light-emitting layer> The light emitting layer is provided above the first conductivity type cladding layer, and the light emitting layer preferably has an emission wavelength of 210 nm or more and 360 nm or less. The light-emitting layer has one or more quantum well layers. In the quantum well layers, materials may be appropriately selected depending on the desired emission wavelength. For example, Al is used as the material for the quantum well layer when the emission wavelength is in the ultraviolet region. b Ga 1-b N(0≦b≦0.8) and so on.

[0023] The light-emitting layer has a structure in which the quantum well layer is sandwiched between layers formed of a material different from that of the quantum well layer, either above or below, or both above and below. Examples of layers formed of a material different from that of the quantum well layer include Al layers having a thickness of 1 nm to 20 nm. c Ga 1-c Examples include the N(0.5≦c<0.7) layer. The light-emitting layer may be partially doped with impurities, such as Si and C. The light-emitting layer may have a structure in which no impurities are intentionally doped (an undoped layer).

[0024] <Waveguide layer> From the perspective of optical confinement, the laser diode of the present embodiment may include a first conductive type waveguide layer disposed between the first conductive type clad layer and the light emitting layer for confining light in the light emitting layer, and a second conductive type waveguide layer disposed between the second conductive type clad layer and the light emitting layer for confining light in the light emitting layer. Thereby, the waveguide layer is formed above and below the light emitting layer so as to sandwich the light emitting layer, and has the effect of confining the light emitted from the light emitting layer within the light emitting layer. That is, the waveguide layer is preferably composed of two layers, namely, a first conductive type waveguide layer disposed on the first conductive type clad layer side with respect to the light emitting layer and a second conductive type waveguide layer disposed on the second conductive type clad layer side with respect to the light emitting layer.

[0025] From the perspective of optical confinement, the waveguide layer is preferably a nitride semiconductor containing Al and Ga having a bandgap higher in energy than the light emitting layer. The waveguide layer preferably has an Al composition and a film thickness that increase the overlap between the electric field intensity distribution of the light standing in the device and the light emitting layer. In particular, the film thickness ratio between the first conductive type waveguide layer and the second conductive type waveguide layer can take various values depending on the optical confinement in the light emitting layer and the Al composition of AlGaN in the first conductive type clad layer and the second conductive type clad layer.

[0026] From the perspective of carrier confinement in the light emitting layer, when the light emitting layer is Al b Ga (1-b) N(0 < b < 1) and the waveguide layer is Al d Ga (1-d) N(0 < d < 1), it is more preferable that b < d and d ≧ b + 0.05. For example, when the light emitting layer having an emission wavelength of 265 nm is taken as an example, b = 0.52, and d is preferably 0.57 or more. Also, from the perspectives of optical confinement and sheet resistance, the total film thickness of the first conductive type waveguide layer and the second conductive type waveguide layer is preferably 70 nm or more and 150 nm or less.

[0027] Although it is preferable that the Al compositions of the first-conductivity-type waveguide layer and the second-conductivity-type waveguide layer are each uniform in the film thickness direction, this is not a strict requirement. In order to avoid light absorption by a metal (for example, the second electrode) present above the second-conductivity-type contact described later, the Al composition of the second-conductivity-type waveguide layer may be higher than that of the first-conductivity-type waveguide layer. For the same purpose, the film thickness of the second-conductivity-type waveguide layer may be thicker than that of the first-conductivity-type waveguide.

[0028] When the first-conductivity-type waveguide layer is an n-type conductive semiconductor layer, in order to obtain the same conductivity type as the first-conductivity-type cladding layer, impurities other than N such as V group elements other than N such as P, As, Sb, and impurities such as H, C, O, F, Mg, Si may be mixed, but this is not a strict requirement.

[0029] <Second-conductivity-type cladding layer> The second-conductivity-type cladding layer is provided on the light-emitting layer. The second-conductivity-type cladding layer has a second-conductivity-type nitride semiconductor layer. The second-conductivity-type cladding layer is formed of, for example, Al e Ga 1-e N(0 < e < 1). Also, when a waveguide layer (second-conductivity-type waveguide layer) is provided on the light-emitting layer, the second-conductivity-type cladding layer is formed in the shape of the waveguide layer (second-conductivity-type waveguide layer). As a result, the second-conductivity-type cladding layer can be easily lattice-matched to the light-emitting layer or the waveguide layer, and the threading dislocation density can be suppressed.

[0030] The second-conductivity-type cladding layer has conductivity sufficient to inject carriers (electrons or holes) into the light-emitting layer, and if it is possible to increase the overlap between the electric field strength distribution of the standing optical mode in the device and the light-emitting layer (that is, increase the optical confinement), the conductivity type is not particularly limited. The second-conductivity-type cladding layer may be, for example, p-type AlGaN doped with Mg in part. When the second-conductivity-type cladding layer is a p-type conductive semiconductor layer, impurities such as V group elements other than N such as P, As, Sb, and impurities such as C, H, F, O, Mg, Si may be mixed, but the types of impurity elements are not limited to this.

[0031] It is more preferable that the entire or a part of the p-type clad layer does not contain p-type impurities such as Mg, B, Be, Si, Li, etc. Since the p-type clad layer does not contain p-type impurities, the oscillation threshold current density of the ultraviolet laser diode can be reduced as compared with the conventional ultraviolet laser diode.

[0032] From the viewpoint of more efficiently injecting carriers into the light-emitting layer, the p-type clad layer is an AlGaN compositionally graded layer in which the Al composition f decreases in the direction away from the upper surface of the substrate. f Ga (1-f) It is preferable to include a p-type vertical conduction layer which is a compositionally graded layer formed of AlGaN and a p-type lateral conduction layer containing AlGaN (0 < g ≦ 1). g Ga (1-g) N(0<g≦1). Hereinafter, the p-type vertical conduction layer and the p-type lateral conduction layer will be described.

[0033] (p-type vertical conduction layer) The p-type vertical conduction layer is a layer that constitutes the region on the light-emitting layer side of the p-type clad layer. The p-type vertical conduction layer is a layer containing AlGaN. The p-type vertical conduction layer may be a layer in which the Al composition ratio continuously decreases from 1.0 in the direction away from the interface between the light-emitting layer and the p-type clad layer. By the inclination of the Al composition in the p-type clad layer, it serves as a light confinement, a carrier injection into the light-emitting layer, and an electron blocking layer, and the effect of reducing the oscillation threshold current density of the laser diode can be obtained.

[0034] ​​​​The profile (gradient) of the Al composition f in the p-type vertical conduction layer may decrease continuously or discontinuously. Here, "decreasing discontinuously" means that the Al composition f is the same (constant in the film thickness direction) in a part of the p-type vertical conduction layer film. That is, the p-type vertical conduction layer may include a portion where the Al composition f does not decrease in the direction away from the substrate, but does not include an increasing portion. By including such a composition gradient layer in the p-type cladding layer, the p-type cladding layer serves as an optical confinement, a carrier injection into the light-emitting layer, and an electron blocking layer, so that an effect of lowering the oscillation threshold current density of the ultraviolet laser diode 100 is expected.

[0035] From the viewpoint of lattice matching, the film thickness of the p-type vertical conduction layer is preferably 500 nm or less. Further, from the viewpoints of optical confinement in the light-emitting layer and carrier injection, the film thickness of the p-type vertical conduction layer is more preferably 250 nm or more and 450 nm or less, and even more preferably 300 nm or more and 400 nm or less.

[0036] (p-type lateral conduction layer) The p-type lateral conduction layer is a layer that constitutes a region on the opposite side of the light-emitting layer in the p-type cladding layer and is formed on the p-type vertical conduction layer. The p-type lateral conduction layer contains Al g Ga 1-g N (0 < g ≦ 1). Here, the Al composition g on the surface of the p-type lateral conduction layer facing the p-type vertical conduction layer is preferably greater than the minimum value of the Al composition f of the p-type vertical conduction layer. For the purpose of controlling the longitudinal resistivity of the p-type lateral conduction layer, impurities such as H, Mg, Be, Zn, Si, and B can be intentionally incorporated. The amount of the incorporated impurities is, for example, 1×10 19 cm -3 or more and 5×10 21 cm -3 depending on the net electric field amount induced on the surface and inside of the p-type lateral conduction layer.

[0037] The thickness of the second conductivity type lateral conduction layer is preferably 20 nm or less, more preferably 10 nm or less, and even more preferably 5 nm or less, from the viewpoint of facilitating quantum transmission of carriers through the second conductivity type lateral conduction layer.

[0038] When a second-conductivity-type contact layer (described later) is provided on the second-conductivity-type lateral conduction layer, the Al composition at the interface between the second-conductivity-type lateral conduction layer and the second-conductivity-type contact layer is preferably smaller than the Al composition in the second-conductivity-type contact layer and is completely strained with respect to the substrate. Such a second-conductivity-type lateral conduction layer can improve lateral conductivity by induced holes at the interface due to a negative net internal electric field accumulated at the surface and inside near the surface of the second-conductivity-type lateral conduction layer.

[0039] The second conductivity type vertical conduction layer has the function of generating carriers (for example, holes when the second conductivity type vertical conduction layer is formed of a p-type semiconductor) by the polarization doping effect and efficiently injecting the carriers into the active layer in the light emitting layer. Therefore, by providing the second conductivity type vertical conduction layer between the light emitting layer and the second conductivity type contact layer, the carrier injection efficiency of the laser diode can be increased and the threshold voltage can be reduced. The second-conductivity-type lateral conduction layer has the effect of spreading the hole distribution in the lateral direction, which is narrowed by the electric field concentrated under the electrode. This effect allows the second-conductivity-type lateral conduction layer to improve the carrier injection efficiency, just like the second-conductivity-type vertical conduction layer.

[0040] (middle class) Between the second conductivity type vertical conduction layer and the second conductivity type waveguide layer, an Al composition h increases in the direction away from the top surface of the substrate from the viewpoint of improving conductivity and / or forming the second conductivity type lateral conduction layer and the second conductivity type contact layer with complete strain. h Ga (1-h)An intermediate layer composed of N (0 < h ≤ 1.0) can be provided. The intermediate layer between the second-conductive-type vertical conduction layer and the second-conductive-type waveguide layer may be a mixed crystal that is not a bandgap that does not absorb light of a desired emission wavelength, and preferably has a film thickness of 50 nm or less, and may be undoped.

[0041] <Second-conductive-type contact layer> The laser diode of this embodiment may further include a second-conductive-type contact layer disposed on the second-conductive-type cladding layer. The nitride semiconductor constituting the second-conductive-type contact layer is preferably formed of, for example, GaN, AlN, or InN and mixed crystals containing them, and more preferably a nitride semiconductor containing GaN.

[0042] The second-conductive-type contact layer may be mixed with impurities other than N such as V group elements other than N such as P, As, Sb, and impurities such as C, H, F, O, Mg, Si, Be. From the versatility of the source gas, the impurity contained in the second-conductive-type contact layer is preferably Mg. From the viewpoint of reducing contact resistance, the concentration of Mg is 8×10 19 cm -3 or more and 5×10 21 cm -3 or less, and more preferably 5×10 20 cm -3 or more and 以5×10 21 cm -3 or less.

[0043] Also, the layer thickness of the second-conductive-type contact layer is preferably 1 nm or more and 20 nm or less. The thinner the layer thickness of the second-conductive-type contact layer, the higher the carrier injection efficiency of the laser diode, and the thicker the layer thickness, the lower the carrier injection efficiency.

[0044] <First electrode> The first electrode is provided on the first conductivity type cladding layer. The first electrode is preferably formed of a first conductive material that is electrically connected to the first conductivity type cladding layer. Examples of the first conductive material include an alloy containing any of Mo, Nb, Zr, Ti, Al, W, Ni, Au, V, and In. Using an alloy containing any of V, Ti, Al, Ni, and Au as the first conductive material can reduce contact resistance.

[0045] <Second electrode> The second electrode is provided on the second conductivity type cladding layer. The second electrode is preferably formed of a second conductive material that is electrically connected to the second conductivity type cladding layer. Examples of the second conductive material include Ti, Pt, Ni, Pd, Au, Pt, Co, Cu, Ni, Ta, and Ru, or alloys containing any of these. Using an alloy containing Ti, Pt, Ni, Au, or Pd as the second conductive material can reduce contact resistance.

[0046] <Mesa structure and resonator> The mesa structure is formed to electrically separate the second conductivity type layer from the first conductivity type layer. The mesa structure is a structure in which a portion of the semiconductor laminate is removed. Here, the "semiconductor laminate" refers to at least the first conductivity type cladding layer, the light emitting layer, and the second conductivity type cladding layer, and also includes the above-mentioned waveguide layers (first conductivity type waveguide layer and second conductivity type waveguide layer), the intermediate layer, and the second conductivity type contact layer, if any.

[0047] The mesa structure preferably has a cavity parallel to the (1-100) crystal orientation plane of the substrate in a plan view, enabling an edge-emitting laser diode that emits light in the <1-100> direction. This is because, when obtaining the cavity mirror end faces of the laser cavity by various methods such as cleavage or etching, the atomically flat (1-100) plane is the easiest to form. In other words, it is preferable that the mesa structure has a cavity in which the mesa end faces are parallel to the (1-100) crystal orientation plane of the substrate in a plan view, and that the edge-emitting laser diode emits light in the <1-100> direction.

[0048] The mesa structure can be formed by etching the nitride semiconductor layer stack using inductively coupled plasma (ICP) etching or similar. Depending on the etching conditions, a large number of dislocations are generated from the side of the mesa structure and propagate toward the interior of the mesa structure. This is because the nitride semiconductor layer stack grows pseudomorphically, lattice-matched to the substrate, and strain accumulates in the nitride semiconductor layer stack. The strain is partially released during the device process, including the formation of the mesa structure, but the release of strain is accompanied by the generation of dislocations in the mesa structure. The generated dislocation lines typically originate from the side of the mesa structure.

[0049] If dislocations in the mesa structure extend to the area below the second electrode, the oscillation threshold current significantly deteriorates. For this reason, it is preferable to provide the second electrode inside the mesa structure, beyond the maximum area of ​​dislocations occurring near the side surface of the mesa structure. This prevents dislocations that occur as the mesa structure is released from reaching the light-emitting layer directly below the second electrode, allowing the oscillation threshold current density to reach the optimum level inherent to the structure. The device resistance of a laser diode is determined by the maximum distance D between the second electrode and the side surface of the mesa structure. From the viewpoint of reducing the device resistance, it is preferable to achieve a smaller D. Therefore, it is necessary to suppress the maximum range of dislocations generated near the side surface of the mesa structure.

[0050] Through extensive research, the applicants have found that specifying the shape of the mesa structure in a plan view makes it possible to suppress the maximum range of dislocations generated near the side surfaces of the mesa structure. The mesa structure preferably has a rectangular shape having long and short sides in a plan view, with the long sides parallel to the <1-100> direction, and the convex portions preferably protrude in at least one of the <11-20> and <-1-120> directions in a plan view. That is, the convex portions are preferably provided on the side surfaces of the mesa structure other than the surfaces on which the resonator mirror end faces are formed. Providing the convex portions makes it possible to concentrate the strain stress of the mesa structure at the tips of the convex portions. Therefore, by intentionally controlling the origin of dislocations introduced into the mesa structure during the stress release process during mesa structure formation, it is possible to efficiently cause dislocation annihilation and suppress the spread of the generated dislocations.

[0051] From the viewpoint of achieving sufficient stress concentration at the top of the protrusions and efficiently generating dislocation pair annihilation, the height of the protrusions in a plan view is preferably 1 μm or more and 11 μm or less, and more preferably 1 μm or more and 3.5 μm or less. If the height of the protrusions is within the above range, it is possible to prevent the unevenness on the side surfaces of the protrusions from being minute, resulting in insufficient stress concentration, or the distance from the bottom to the top of the protrusions from being large, resulting in a decrease in the frequency of dislocation meetings and an expansion of the maximum range of dislocations.

[0052] Furthermore, from the viewpoint of achieving sufficient stress concentration at the apex of the convex portion, the minimum angle formed by the line segments connecting the bottom and apex of the convex portion in a planar view (hereinafter sometimes referred to as the angle of the convex apex) is preferably 1 degree or more and 130 degrees or less, and more preferably greater than 1 degree and 120 degrees or less. When the minimum angle of the convex apex is within the above range, the convex portion is less likely to be damaged, and sufficient stress concentration at the apex of the convex portion can be achieved by suppressing insufficient stress concentration due to minute unevenness on the side surface of the convex portion.

[0053] Furthermore, from the viewpoint of suppressing dislocation propagation toward the inside of the mesa, the distance between the apexes of the multiple protrusions, which are the starting points for dislocation generation, is preferably 1 μm or more and 10 μm or less, and more preferably 1 μm or more and 6 μm or less. When the distance between the apexes of the protrusions is within the above-mentioned range, the protrusions can be easily formed, and generated dislocations can be efficiently merged to suppress dislocation propagation toward the inside of the mesa.

[0054] (1.2) Laser diode manufacturing method The laser diode of this embodiment is manufactured through a process of forming each layer on a substrate.

[0055] (Formation of substrate) The substrate is formed by a general substrate growth method such as a vapor phase growth method such as sublimation or hydride vapor phase epitaxy (HVPE) or a liquid phase growth method.

[0056] (Formation of semiconductor laminate) Each layer of the semiconductor laminate formed on the substrate can be formed by, for example, molecular beam epitaxy (MBE), hydride vapor phase epitaxy (HVPE), or metal organic chemical vapor deposition (MOCVD). Here, among the layers formed on the substrate, the nitride semiconductor layer can be formed using, for example, an Al raw material containing trimethylaluminum (TMAl), a Ga raw material containing trimethylgallium (TMGa) or triethylgallium (TEGa), or an N raw material containing ammonia (NH3). Laser diodes are manufactured through a process of removing unnecessary portions of each layer of a semiconductor laminate formed on a substrate by etching, which can be performed by, for example, inductively coupled plasma (ICP) etching.

[0057] (Electrode formation) Laser diodes can be manufactured through a process of forming electrodes. Electrodes such as the first electrode and the second electrode can be formed by, for example, resistance heating evaporation, electron gun evaporation, or sputtering, but are not limited to these methods. The electrodes can be formed as a single layer or as a multi-layer stack. After the electrodes are formed, they can be heat-treated in an oxygen, nitrogen, or air atmosphere. Finally, the substrate on which the layers have been formed through the above-described steps is diced into individual pieces to manufacture the laser diodes.

[0058] 2. Examples of laser diodes Next, the laser diode of this embodiment will be described in more detail with reference to the drawings. The detailed configuration of each layer in each of the following specific examples is as described above.

[0059] (3.1) First embodiment FIG. 1A is a plan view schematic diagram showing the planar configuration of a laser diode 1 according to the first embodiment, and FIG. 1B is a cross-sectional view schematic diagram showing the cross-sectional configuration of a plane perpendicular to the optical resonance direction of the laser diode 1 shown in FIG. 1A. In Figures 1A and 1B, <1-100><11-20> <0001> <-1-120> indicates the crystal orientation.

[0060] 1A, the laser diode 1 of this embodiment includes a substrate 10 containing Al and a semiconductor laminate portion 20 disposed on the substrate 10. The laser diode 1 also includes a first electrode and a second electrode (not shown). The semiconductor laminate 20 has a first conductivity type cladding layer 21 including a first conductivity type nitride semiconductor layer, a light emitting layer 22 formed of a nitride semiconductor including one or more quantum wells, and a second conductivity type cladding layer 23 including a second conductivity type nitride semiconductor layer. A part of the first conductivity type cladding layer 21, the light emitting layer 22, and the second conductivity type cladding layer 23 form a mesa structure 201 for optical resonance and emission.

[0061] 1A, among the side surfaces of the mesa structure 201, the side surfaces parallel to the optical resonance direction D1 have multiple convex portions in a planar view. The multiple convex portions may be provided on all side surfaces that are not perpendicular to the optical resonance direction D1 as shown in FIG. 1A, or may be provided on one side surface. Furthermore, the multiple convex portions may be provided over the entire region of the side surface of the mesa structure 201, or may be provided only in a partial region.

[0062] The plurality of protrusions will be described in detail with reference to FIGS. 2A to 2C. 2A to 2C are schematic plan views showing examples of the shapes of multiple protrusions, each showing the distance W between the apexes of the protrusions, the height H of the protrusions (the distance from the base of the protrusion to the apex of the protrusion), and the minimum angle φ formed by the line segment connecting the base of the side surface to the apex of the protrusion. The pattern of the multiple protrusions may be a continuous arrangement of triangular protrusions in a plan view as shown in Fig. 2A, or protrusions with arc-shaped tops in a plan view as shown in Fig. 2B, or protrusions with triangular tops in a plan view arranged at intervals as shown in Fig. 2C. From the viewpoint of achieving sufficient stress concentration at the tops of the protrusions, it may be preferable that the tops of the protrusions are not flat, as shown in all of Figs. 2A to 2C.

[0063] (3.2) Second embodiment 3 is a schematic diagram for explaining a laser diode 2 according to the second embodiment. FIG. 3 is a schematic cross-sectional view of the laser diode 2. The laser diode 2 differs from the laser diode 1 according to the first embodiment in that it has a semiconductor laminate 20A that further includes a waveguide layer 24 of a first conductivity type and a waveguide layer 25 of a second conductivity type. In such a laser diode 2, the light confinement effect in the light emitting layer 22 is improved, and the light emission intensity is improved.

[0064] (3.3) Third embodiment 4 is a schematic diagram for explaining a laser diode 3 according to the third embodiment. FIG. 4 is a schematic cross-sectional view of the laser diode 3. The laser diode 3 differs from the laser diode 2 according to the second embodiment in that it has a semiconductor laminate portion 20B including a second conductivity type contact layer 26 disposed on a second conductivity type cladding layer 23. In such a laser diode 3, the efficiency of carrier injection into the light-emitting layer 22 is improved, and the light-emitting efficiency is improved.

[0065] The second-conductivity-type contact layer 26 may be combined with, for example, the laser diode 2 according to the second embodiment. That is, the laser diode may have the second-conductivity-type contact layer 26 disposed on the second-conductivity-type cladding layer 23 of the laser diode 2 (not shown).

[0066] (3.4) Fourth embodiment 5 is a schematic diagram for explaining a laser diode 4 according to the fourth embodiment. FIG. 5 is a schematic cross-sectional view of the laser diode 4. The laser diode 4 differs from the laser diode 1 according to the first embodiment in that it has a semiconductor laminate portion 20C including a second conductivity type cladding layer 23 composed of a second conductivity type vertical conduction layer 23A and a second conductivity type horizontal conduction layer 23B, and a second conductivity type contact layer 26. In such a laser diode 4, the efficiency of carrier injection into the light-emitting layer 22 is improved, and the light-emitting efficiency is improved.

[0067] (3.5) Fifth embodiment 6 is a schematic diagram for explaining a laser diode 5 according to the fifth embodiment. FIG. 6 is a schematic cross-sectional view of the laser diode 5. The laser diode 5 differs from the laser diode 1 according to the first embodiment in that it has a semiconductor laminate 20D including a first conductivity type waveguide layer 24, a second conductivity type waveguide layer 25, a second conductivity type cladding layer composed of a second conductivity type vertical conductive layer 23A and a second conductivity type lateral conductive layer 23B, and an intermediate layer 27 provided between the second conductivity type vertical conductive layer 23A and the second conductivity type waveguide layer 25. In the laser diode 5, the carrier conductivity in the intermediate layer 27 is improved, and the second conductivity type lateral conduction layer 23B and the second conductivity type contact layer 26 are formed with complete strain, thereby improving the carrier lateral conduction.

[0068] (3.6) Sixth embodiment 7 is a schematic diagram for explaining a laser diode 6 according to the sixth embodiment. FIG. 7 is a schematic cross-sectional view of the laser diode 6. The laser diode 6 differs from the laser diode 1 according to the first embodiment in that it further includes a first-conductivity-type waveguide layer 24, a second-conductivity-type waveguide layer 25, and a second-conductivity-type contact layer 26, and the mesa structure of the laser diode 6 is a two-stage structure, and has a semiconductor laminate portion 20E including a mesa structure 201 including a first-conductivity-type cladding layer 21 and a mesa structure 203 not including the first-conductivity-type cladding layer 21.

[0069] 4.Effects The laser diode of the present disclosure described above has the following advantages. (1) The laser diode has a mesa structure for optical resonance and emission formed in at least a part of the semiconductor laminate, and has a plurality of protrusions on the side surfaces that are not perpendicular to the optical resonance direction. This makes it possible to concentrate the strain stress of the mesa structure at the tip of the protrusion, thereby controlling the origin of dislocations introduced into the mesa structure during the stress release process when the mesa structure is formed.

[0070] (2) In the laser diode, the distance between the tops of the plurality of protrusions in plan view is preferably 1 μm or more and 10 μm or less. This makes it possible to efficiently merge the generated dislocations and suppress the propagation of dislocations toward the inside of the mesa. (3) In the laser diode, it is preferable that the height of the convex portion in a plan view is 1 μm or more and 11 μm or less. This reduces the frequency of association of the generated dislocations, thereby suppressing the expansion of the maximum range of dislocations.

[0071] (4) In the laser diode, the minimum angle formed by the line segments connecting the bottom and top of the convex portion in a plan view is 1 degree or more and 120 degrees or less. This allows sufficient stress concentration at the top of the projection. (5) In the laser diode, the mesa structure preferably has a resonator in which the end faces parallel to the (1-100) crystal orientation plane of the nitride semiconductor substrate are resonator mirror end faces, and the laser diode is an edge-emitting ultraviolet laser diode that emits light in the <1-100> direction. This allows the resonator mirror end faces of the laser resonator to be easily formed on atomically flat (1-100) surfaces.

[0072] (6) In the laser diode, it is preferable that the mesa structure has a rectangular shape having long and short sides in plan view, the long sides are parallel to the <1-100> direction, and the convex portion protrudes in at least one of the <11-20> direction and the <-1-120> direction in plan view. This allows the provision of a convex portion that can reduce the maximum range of dislocations by concentrating the strain stress of the mesa structure on the side surfaces other than the surface on which the resonator mirror end faces are formed. (7) In the laser diode, the nitride semiconductor substrate is preferably an AlN single crystal substrate. This reduces the difference in lattice constant with the nitride semiconductor layer formed above the substrate, and the nitride semiconductor layer can be grown in a lattice-matched system, thereby reducing threading dislocations.

[0073] (8) In the laser diode, it is preferable to provide a first conductivity type waveguide layer and a second conductivity type waveguide layer above and below the light emitting layer, which confine light in the light emitting layer. This improves the effect of confining light in the light-emitting layer, thereby improving the luminous efficiency.

[0074] (9) The laser diode further comprises a second conductivity type contact layer containing GaN on the second conductivity type cladding layer, and the second conductivity type cladding layer is Al f Ga 1-fIt includes N (0.1 ≦ f ≦ 1) and has a composition gradient in which the Al composition f decreases as it moves away from the nitride semiconductor substrate, and has a second-conductive-type vertical conduction layer with a film thickness of less than 0.5 μm, and Al g Ga 1-g It preferably has a second-conductive-type lateral conduction layer containing N (0 < g ≦ 1). Thereby, carriers can be more efficiently injected into the light-emitting layer to improve the light-emitting efficiency.

[0075] (10) In the laser diode, it is preferably provided with an intermediate layer formed of Al h Ga 1-h N (0 < h ≦ 1.0), which is disposed between the second-conductive-type vertical conduction layer and the second-conductive-type waveguide layer. Thereby, the second-conductive-type lateral conduction layer and the second-conductive-type contact layer can be formed with complete strain to improve the conductivity of carriers. (11) In the laser diode, the film thickness of the second-conductive-type vertical conduction layer is preferably 250 nm or more and 450 nm or less. Thereby, the light confinement effect on the light-emitting layer is improved, the carrier injection effect is improved, and the light-emitting efficiency of the laser diode is improved.

[0076] (12) In the laser diode, it is preferable that a part or all of the regions including the interface with the second-conductive-type waveguide layer in the second-conductive-type vertical conduction layer are regions not doped with impurities. Thereby, the diffusion of impurities can be suppressed, carriers can be efficiently injected into the light-emitting layer, and the oscillation efficiency can be increased.

[0077] (13) In the laser diode, the first-conductive-type cladding layer is formed of Al a Ga 1-a N (0.6 < a ≦ 0.8), and it is preferable that the second-conductive-type vertical conduction layer and the second-conductive-type lateral conduction layer are formed with complete strain with respect to the nitride semiconductor substrate. The first-conductive-type cladding layer is Al a Ga 1-aBy forming with N(0.6 < a ≤ 0.8), the second-conductivity-type vertical conduction layer and the second-conductivity-type horizontal conduction layer can be formed with perfect strain with respect to the substrate, and the conductivity of carriers can be improved. (14) In the laser diode, it is preferable that the Al composition g on the surface of the second-conductivity-type horizontal conduction layer facing the second-conductivity-type vertical conduction layer is larger than the minimum value of the Al composition f. Thereby, carriers can be diffused in the lateral direction, and the injection efficiency of carriers can be enhanced.

Example

[0078] Hereinafter, examples and comparative examples of the present disclosure will be described.

[0079] <Example 1> An (0001) plane AlN single crystal substrate with a thickness of 550 μm was used as the substrate, and annealing treatment was performed on this substrate using a metalorganic chemical vapor deposition (MOCVD) apparatus. The annealing treatment was carried out as one set including annealing for 5 minutes in an NH3 atmosphere and annealing for 5 minutes in a H2 atmosphere under an environment of 1300 °C, and two sets of treatments were performed.

[0080] Next, an AlN layer, which is a homoepitaxial layer, was formed as a buffer layer on the substrate. The AlN layer was formed with a thickness of 500 nm under an environment of 1200 °C. At this time, the ratio (V / III ratio) of the supply rate of the group III element source gas to the supply rate of the nitrogen source gas was 50. Also, the degree of vacuum in the chamber where annealing was performed was 50 mbar. The growth rate of the AlN layer at this time was 0.5 μm / hr. Also, trimethylaluminum (TMAl) was used as the Al source. Also, ammonia (NH3) was used as the N source.

[0081] On the AlN layer formed as described above, a first-conductivity-type cladding layer was formed. The first-conductivity-type cladding layer is an n-type AlGaN layer (Al: 70%, that is, Al 0.70 Ga 0.30The first conductivity type cladding layer was formed to a thickness of 350 nm under the conditions of a temperature of 1080°C, a degree of vacuum of 50 mbar, and a V / III ratio of 4000. The growth rate of the first conductivity type cladding layer was 0.4 μm / hr. Trimethylaluminum (TMAl) was used as the Al source, triethylgallium (TEGa) was used as the Ga source, ammonia (NH3) was used as the N source, and monosilane (SiH4) was used as the Si source.

[0082] Next, an n-type waveguide layer, which is a first conductivity type waveguide layer, was formed on the first conductivity type cladding layer. The n-type waveguide layer was an n-type AlGaN layer (Al: 63%, i.e., Al 0.63 Ga 0.37 The n-type waveguide layer was formed to a thickness of 60 nm under the conditions of a temperature of 1080°C, a degree of vacuum of 50 mbar, and a V / III ratio of 4000. The growth rate of the n-type waveguide layer was 0.35 μm / hr. Trimethylaluminum (TMAl) was used as the Al source, triethylgallium (TEGa) was used as the Ga source, and ammonia (NH3) was used as the N source.

[0083] Next, a light-emitting layer was formed on the n-type waveguide layer. The light-emitting layer was formed to have a multi-quantum well structure in which quantum well layers and barrier layers were stacked three times. Here, the quantum well layer was an AlGaN layer (Al: 52%, i.e., Al) with a thickness of 3.0 nm. 0.52 Ga 0.48 The barrier layer having a thickness of 6.0 nm was an AlGaN layer (Al: 63%, i.e., Al 0.63 Ga 0.37 N layer). The light-emitting layer was formed under conditions of a vacuum of 50 mbar and a V / III ratio of 4000. The growth rate of the quantum well layer was 0.18 μm / hr, and the growth rate of the barrier layer was 0.15 μm / hr.

[0084] Next, a p-type waveguide layer, which is a second conductive type waveguide layer, was formed on the light emitting layer. The p-type waveguide layer was an AlGaN layer containing no dopant (Al: 63%, i.e., Al 0.63 Ga 0.37 The p-type waveguide layer was formed to a thickness of 60 nm at a temperature of 1080°C, a vacuum of 50 mbar, and a V / III ratio of 4000. The growth rate of the p-type waveguide layer was 0.35 μm / hr. Trimethylaluminum (TMAl) was used as the Al source, and triethylgallium (TEGa) was used as the Ga source.

[0085] Next, a second-conductivity-type cladding layer was formed on the p-type waveguide layer. The second-conductivity-type cladding layer had a layered structure including a second-conductivity-type vertical conduction layer and a second-conductivity-type lateral conduction layer, and was a graded layer with a gradient Al composition ratio. The second-conductivity-type vertical conduction layer was a 20-nm-thick p-type AlGaN layer with an Al composition distribution ranging from Al = 0.63 to 1.0 in the direction away from the substrate. The second-conductivity-type lateral conduction layer was a 320-nm-thick p-type AlGaN layer with an Al composition distribution ranging from Al = 1.0 to 0.7 in the direction away from the substrate. The second-conductivity-type cladding layer was formed at a temperature of 1080°C, a vacuum of 50 mbar, and a V / III ratio of 4000. The growth rate of the second-conductivity-type cladding layer was 0.3 to 0.5 μm / hr. Trimethylaluminum (TMAl) was used as the Al source. In addition, triethylgallium (TEGa) was used as the Ga source material.

[0086] Next, a p-type contact layer, which is a second conductivity type contact layer, was formed on the second conductivity type cladding layer. Here, the p-type contact layer was formed from an AlGaN layer and a GaN layer. The AlGaN layer was a p-type nitride semiconductor layer with a thickness of 30 nm, using Mg as a dopant impurity and with an Al composition distribution that varied from Al = 0.7 to 0.4 in the direction away from the substrate. The GaN layer was formed from GaN (i.e., Al: 0%) with a thickness of 10 nm.

[0087] The p-type contact layer was formed at a temperature of 950° C., under a vacuum of 150 mbar, with a V / III ratio of 3650. The growth rate of the p-type contact layer was 0.2 μm / hr.

[0088] In this way, a semiconductor laminate was formed on an AlN substrate. Reciprocal lattice mapping measurements were performed on this semiconductor laminate using XRD, and it was found that the semiconductor laminate had undergone pseudomorphic growth without relaxation up to the p-type contact layer.

[0089] The semiconductor laminated portion formed as described above was annealed in an N2 atmosphere at 700°C for 10 minutes or more to further reduce the resistance of the p-type contact layer. A resist pattern (a photoresist mask for IPC etching) was formed on the p-type contact layer using photolithography to create multiple protrusions at the mesa boundary in the <1-100> direction. Next, the n-type cladding layer was exposed by dry etching using an ICP with a gas containing Cl2 and BCl3. The n-type cladding layer was formed into a rectangular region elongated in the <1-100> direction in plan view. The ICP conditions were: antenna power 320 W, bias power 30 W, automatic pressure regulation (APC: Adaptive Pressure Control valve) 2 Pa, process pressure 600 Pa, and gas flow rates of Cl2 gas 20 sccm and BCl3 gas 5 sccm.

[0090] The formed mesa structure had a length of 600 μm in the <1-100> direction and a length of 40 μm in the <11-20> direction. Here, the length of the mesa structure in the <1-100> direction is the distance between the cavity mirror end faces in a plan view, and the length in the <11-20> direction is the distance between the side faces of the mesa structure.

[0091] On the p-type contact layer of the mesa structure, Ni and Au films were sequentially deposited in the shape of rectangles elongated in the <1-100> direction to form multiple second electrodes, each 5 μm wide and 600 μm long. Monochromatic cathode luminescence measurement was performed on the mesa structure at the emission wavelength, and the width of the dislocation generation region around the mesa structure, which becomes the non-emitting region, was confirmed to be 5.6 μm. From the viewpoint of reducing the oscillation threshold of the laser diode, the second electrode was placed 5.6 μm away from the side of the mesa structure so that the second electrode and the dislocation generation region around the mesa structure would not overlap.

[0092] In addition, in the region where the n-type cladding layer of the mesa structure was exposed, V, Al, Ni, Ti, and Au were deposited in order in a rectangular shape elongated in the <1-100> direction to form multiple electrode metal regions to serve as first electrodes. Furthermore, within the electrode metal regions, the substrate was divided into stripes by multiple cleavage in the <11-20> direction, forming individual laser diodes. The final length of the mesa structure in the <1-100> direction was 600 μm.

[0093] When the shape of the side surface of the mesa structure in the <1-100> direction (the side surface other than the cavity mirror end face) was measured in a plan view, the distance between the apexes of the convex portions was 1.0 μm, the height of the convex portions was 1.0 μm, and the minimum angle between the line segments connecting the bottom and top of the convex portions was 20 degrees. The element resistance of the laser diode was 5.4 Ω.

[0094] <Example 2> A laser diode was obtained in the same manner as in Example 1, except that the shape of the side surface of the mesa structure was changed by changing the shape of the photoresist mask. The planar shape of the side surface (not the cavity mirror end surface) of the mesa structure of the obtained laser diode in the <1-100> direction was measured. The distance between the apexes of the convex portions was 6 μm, the height of the convex portions was 1 μm, and the minimum angle between the line segments connecting the bottom and top of the convex portions was 20 degrees. The width of the non-light-emitting region around the mesa structure was measured and found to be 10.5 μm. When the second electrode was placed 10.5 μm away from the side surface of the mesa structure so that it did not overlap with the dark line region around the mesa structure, the element resistance of the laser diode was 7 Ω.

[0095] Example 3 A laser diode was obtained in the same manner as in Example 1, except that the shape of the side surface of the mesa structure was changed by changing the shape of the photoresist mask. The planar shape of the side surface (the side surface other than the cavity mirror end face) of the mesa structure of the obtained laser diode in the <1-100> direction was measured. The distance between the apexes of the convex portions was 12 μm, the height of the convex portions was 1 μm, and the minimum angle between the line segments connecting the bottom and top of the convex portions was 20 degrees. The width of the non-light-emitting region around the mesa structure was measured and found to be 11.4 μm. When the second electrode was positioned 11.4 μm away from the side surface of the mesa structure so that it did not overlap with the dark line region around the mesa structure, the device resistance of the laser diode was 7.4 Ω.

[0096] Example 4 A laser diode was obtained in the same manner as in Example 1, except that the shape of the side surface of the mesa structure was changed by changing the shape of the photoresist mask. The planar shape of the side surface (not the cavity mirror end surface) of the mesa structure of the obtained laser diode in the <1-100> direction was measured. The distance between the apexes of the convex portions was 5 μm, the height of the convex portions was 3.5 μm, and the minimum angle between the line segments connecting the bottom and top of the convex portions was 20 degrees. The width of the non-light-emitting region around the mesa structure was measured and found to be 9.3 μm. When the second electrode was positioned 9.3 μm away from the side surface of the mesa structure so that it did not overlap with the dark line region around the mesa structure, the device resistance of the laser diode was 6.6 Ω.

[0097] <Example 5> A laser diode was obtained in the same manner as in Example 1, except that the shape of the side surface of the mesa structure was changed by changing the shape of the photoresist mask. The planar shape of the side surface (not the cavity mirror end surface) of the mesa structure of the obtained laser diode in the <1-100> direction was measured. The distance between the apexes of the convex portions was 5 μm, the height of the convex portions was 10 μm, and the minimum angle between the line segments connecting the bottom and top of the convex portions was 20 degrees. The width of the non-light-emitting region around the mesa structure was measured and found to be 11.3 μm. When the second electrode was positioned 11.3 μm away from the side surface of the mesa structure so that it did not overlap with the dark line region around the mesa structure, the device resistance of the laser diode was 7.3 Ω.

[0098] Example 6 A laser diode was obtained in the same manner as in Example 1, except that the shape of the side surface of the mesa structure was changed by changing the shape of the photoresist mask. The planar shape of the side surface (not the cavity mirror end surface) of the mesa structure of the obtained laser diode in the <1-100> direction was measured. The distance between the apexes of the convex portions was 5 μm, the height of the convex portions was 12 μm, and the minimum angle between the line segments connecting the bottom and top of the convex portions was 20 degrees. The width of the non-light-emitting region around the mesa structure was measured and found to be 11.6 μm. When the second electrode was positioned 11.6 μm away from the side surface of the mesa structure so that it did not overlap with the dark line region around the mesa structure, the device resistance of the laser diode was 7.4 Ω.

[0099] Example 7 A laser diode was obtained in the same manner as in Example 1, except that the shape of the side surface of the mesa structure was changed by changing the shape of the photoresist mask. The planar shape of the side surface (the side surface other than the cavity mirror end face) of the mesa structure of the obtained laser diode in the <1-100> direction was measured. The distance between the apexes of the convex portions was 5 μm, the height of the convex portions was 1 μm, and the minimum angle between the line segments connecting the bottom and top of the convex portions was 10 degrees. The width of the non-light-emitting region around the mesa structure was measured and found to be 5.4 μm. When the second electrode was placed 5.4 μm away from the side surface of the mesa structure so that it did not overlap with the dark line region around the mesa structure, the element resistance of the laser diode was 5.3 Ω.

[0100] Example 8 A laser diode was obtained in the same manner as in Example 1, except that the shape of the side surface of the mesa structure was changed by changing the shape of the photoresist mask. The planar shape of the side surface (the side surface other than the cavity mirror end face) of the mesa structure of the obtained laser diode in the <1-100> direction was measured. The distance between the apexes of the convex portions was 5 μm, the height of the convex portions was 1 μm, and the minimum angle between the line segments connecting the bottom and top of the convex portions was 60 degrees. The width of the non-light-emitting region around the mesa structure was measured and found to be 7.9 μm. When the second electrode was placed 7.9 μm away from the side surface of the mesa structure so that it did not overlap with the dark line region around the mesa structure, the element resistance of the laser diode was 6.1 Ω.

[0101] Example 9 A laser diode was obtained in the same manner as in Example 1, except that the shape of the side surface of the mesa structure was changed by changing the shape of the photoresist mask. The planar shape of the side surface (the side surface other than the cavity mirror end face) of the mesa structure of the obtained laser diode in the <1-100> direction was measured. The distance between the apexes of the convex portions was 5 μm, the height of the convex portions was 1 μm, and the minimum angle between the line segments connecting the bottom and top of the convex portions was 100 degrees. The width of the non-light-emitting region around the mesa structure was measured to be 9.5 μm. When the second electrode was positioned 9.5 μm away from the side surface of the mesa structure so that it did not overlap with the dark line region around the mesa structure, the device resistance of the laser diode was 6.7 Ω.

[0102] Example 10 A laser diode was obtained in the same manner as in Example 1, except that the shape of the side surface of the mesa structure was changed by changing the shape of the photoresist mask. The planar shape of the side surface (the side surface other than the cavity mirror end face) of the mesa structure of the obtained laser diode in the <1-100> direction was measured. The distance between the apexes of the convex portions was 1 μm, the height of the convex portions was 1 μm, and the minimum angle between the line segments connecting the bottom and top of the convex portions was 130 degrees. The width of the non-light-emitting region around the mesa structure was measured to be 11.2 μm. When the second electrode was positioned 11.2 μm away from the side surface of the mesa structure so that it did not overlap with the dark line region around the mesa structure, the element resistance of the laser diode was 7.3 Ω.

[0103] <Comparative Example 1> A laser diode was obtained in the same manner as in Example 1, except that the shape of the side surface of the mesa structure was changed by changing the shape of the photoresist mask. The planar shape of the side surface (the side surface other than the cavity mirror end face) in the <1-100> direction of the mesa structure of the obtained laser diode was measured, and no protrusions were found. The width of the non-light-emitting region around the mesa structure was measured and found to be 12 μm. When the second electrode was placed 12 μm away from the side surface of the mesa structure so that it did not overlap with the dark line region around the mesa structure, the element resistance of the laser diode was 7.5 Ω. Table 1 below shows the evaluation results of each example and each comparative example.

[0104] [Table 1]

[0105] As shown in Table 1, the laser diodes of Examples 1 to 10, which have convex portions on the side surfaces of the mesa structure of the laser diode, had lower element resistance compared to the laser diode of Comparative Example 1, which did not have convex portions on the side surfaces of the mesa structure. Furthermore, the laser diodes of Examples 1 and 2, in which the distance between the tops of the convex portions formed on the side surfaces of the mesa structure was 1 μm or more and 10 μm or less, had an even lower element resistance than the laser diode of Example 3, in which the distance between the tops of the convex portions exceeded 10 μm.

[0106] Furthermore, the laser diodes of Examples 7 to 9, in which the minimum angle between the line segments connecting the bottom and top of the convex portion is greater than 1 degree and less than 120 degrees, had an even lower element resistance than the laser diode of Example 10, in which the minimum angle exceeded 120 degrees. Thus, it was found that in order to reduce the element resistance of the laser diode, it is preferable to provide a convex portion on the side surface of the mesa structure, and it is even more preferable to adjust the shape of the convex portion (distance between vertices, height, angle of the vertex in a planar view).

[0107] Although the embodiments of the present disclosure have been described above, the technical scope of the present disclosure is not limited to the technical scope described in the above-described embodiments. Various modifications and improvements can be made to the above-described embodiments, and it is clear from the claims that such modifications and improvements can also be included in the technical scope of the present disclosure. [Explanation of symbols]

[0108] 10 Substrate 20 Semiconductor laminated section 21 First conductive type cladding layer 22 Light-emitting layer 23 Second conductivity type cladding layer 23A Second conductivity type vertical conductive layer 23B Second conductivity type lateral conduction layer 24 First conductivity type waveguide layer 25 Second conductivity type waveguide layer 26 Second conductivity type contact layer 27 Middle Class 28 Convex part 31 1st electrode 32 2nd electrode 201 Mesa structure including first conductivity type cladding layer Side of SS mesa structure End face of ES mesa structure

Claims

1. a nitride semiconductor substrate containing Al; a semiconductor laminate portion disposed on the nitride semiconductor substrate; Equipped with The semiconductor laminate portion is a first conductivity type cladding layer including a first conductivity type nitride semiconductor layer disposed on the nitride semiconductor substrate; a light emitting layer formed of a nitride semiconductor including one or more quantum wells and disposed on the first conductive type cladding layer; a second conductivity type cladding layer including a second conductivity type nitride semiconductor disposed on the light emitting layer; having At least a portion of the semiconductor laminate is a mesa structure including at least the first conductive type cladding layer, the mesa structure being formed for optical resonance and emission; The side surface of the mesa structure that is not perpendicular to the optical resonance direction has a plurality of protrusions. Laser diode.

2. The distance between the tops of the plurality of protrusions in a plan view is 1 μm or more and 10 μm or less.

2. The laser diode of claim 1.

3. The height of the convex portion in a plan view is 1 μm or more and 11 μm or less.

3. The laser diode according to claim 1 or 2.

4. In a plan view, the minimum angle between the line segments connecting the bottom and the top of the protrusion is 1 degree or more and 120 degrees or less.

4. A laser diode according to claim 1.

5. The mesa structure has a resonator in which the end faces parallel to the (1-100) crystal orientation plane of the nitride semiconductor substrate are resonator mirror end faces, and is an edge-emitting ultraviolet laser diode that emits light in the <1-100> direction.

5. A laser diode according to claim 1.

6. The mesa structure has a rectangular shape having long sides and short sides in a plan view, the long sides being parallel to the <1-100> direction, The convex portion protrudes in at least one of the <11-20> direction and the <-1-120> direction in a plan view.

6. A laser diode according to claim 1.

7. The nitride semiconductor substrate is an AlN single crystal substrate.

7. A laser diode according to claim 1.

8. a first conductivity type waveguide layer disposed between the first conductivity type cladding layer and the light emitting layer to confine light to the light emitting layer; a second conductive type waveguide layer disposed between the second conductive type cladding layer and the light emitting layer to confine light to the light emitting layer; Equipped with 8. A laser diode according to claim 1.

9. a second conductive type contact layer disposed on the second conductive type cladding layer and formed of a nitride semiconductor containing GaN; The second conductive type cladding layer is made of Al ｆ G １－ｆ a second conductivity type vertical conduction layer having a thickness of less than 0.5 μm, the second conductivity type vertical conduction layer including N (0.1≦f≦1), the Al composition e of which decreases with increasing distance from the nitride semiconductor substrate; ｇ G １－ｇ N (0<g≦1), 9. The laser diode of claim 8.

10. an Al layer disposed between the second conductive type vertical conduction layer and the second conductive type waveguide layer; ｈ G １－ｈ N (0<h≦1.0), 10. The laser diode of claim 9.

11. The thickness of the second conductive type vertical conductive layer is 250 nm or more and 450 nm or less.

11. The laser diode according to claim 9 or 10.

12. a part or all of a region of the second conductive type vertical conduction layer including an interface with the second conductive type waveguide layer is a region that is not doped with impurities; 12. A laser diode according to any one of claims 9 to 11.

13. The first conductive type cladding layer is made of Al ａ G １－ａ N (0.6<a≦0.8), the second conductive type vertical conduction layer and the second conductive type lateral conduction layer are formed with complete strain with respect to the nitride semiconductor substrate; 13. A laser diode according to any one of claims 9 to 12.

14. the Al composition g of the second conductive type lateral conduction layer at a surface facing the second conductive type vertical conduction layer is greater than a minimum value of the Al composition f of the second conductive type vertical conduction layer; 14. A laser diode according to any one of claims 9 to 13.

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