Laser diode with a cross-conduction layer

Abstract

A laser diode (1) comprising: an AlN single-crystal substrate (11); an n-type cladding layer (12) formed on the substrate (11) and comprising a nitride semiconductor layer with n-type conductivity; a light-emitting layer (14) formed on the n-type cladding layer (12) and comprising one or more quantum wells; a p-type cladding layer (20) formed on the light-emitting layer (14) and comprising a nitride semiconductor layer with p-type conductivity; and a p-type contact layer (18) formed on the p-type shell layer (20) comprising a nitride semiconductor comprising GaN; wherein the p-type shell layer (20) comprises a p-type longitudinal conduction layer (16) comprising AlsGas1-sN (0.3 ≤ s ≤ 1), having a composition gradient such that the Al composition s decreases with increasing distance from the substrate (11), and having a film thickness of less than 0.5 µm;and a p-type cross-conducting layer (17) comprising AltGa1-tN (0.3 < t ≤ 1), wherein, at a surface of the p-type cross-conducting layer (17) adjacent to the p-type longitudinal-conducting layer (16), the Al composition t is greater than a minimum value of the Al composition s.;

Description

CROSS REFERENCE TO RELATED APPLICATIONThe present application claims priority to Japanese Patent Application No. 2019-177788 filed on Sep. 27, 2019, the entire contents of which are incorporated herein by reference.TECHNICAL FIELDThe present disclosure relates to a laser diode.BACKGROUNDNitride semiconductors containing Al and Ga are suitable as materials for laser diodes because they achieve high recombination performance and high optical gain due to their form of direct junction recombination. Particularly, in an Al x Ga 1-x N solid solution system having a high Al composition, in order to obtain an emission wavelength in the ultraviolet region having a wavelength of 300 nm or less, the emission power, the lifetime, and the optical gain of the laser diode largely depend on the crystal defect density. By growing Al x Ga 1-x N-mixed crystals on an AlN single crystal substrate introduced in recent years, a good nitride semiconductor having a reduced defect density can be obtained. This can greatly improve the characteristics of laser diodes. However, in an Al x Ga 1-x N mixed crystal system having a high Al composition, it is difficult to achieve p-type conductivity in Al x Ga 1-x N mixed crystals by doping with impurities. In this connection, for example, Patent Literature (PTL) 1 describes a method of using a gradient layer to improve charge carrier injection efficiency.Citation ListPatent LiteraturePTL 1: JP 2018-532265 APTL 2: US 2017 / 0 309 781 A1PTL 3: US 2019 / 0 103 509 A1PTL 4: US 2013 / 0 099 141 A1PTL 5: U.S. Pat. No. 6,031,858 AUS 2017 / 0 309 781 A1 describes light emitting devices containing graded layers with compositional offset at one or both end points of the graded layer to promote the formation of two dimensional carrier gases and polarization doping and thereby improve device performance.US 2019 / 0 103 509 A1 describes a heterostructure for an optoelectronic device. The heterostructure includes an active region containing at least one quantum well and at least one barrier, and an electron blocking layer located adjacent the active region, the electron blocking layer comprising a graded composition region. An asymmetric p-type superlattice layer is adjacent to the electron blocking layer, wherein the p-type superlattice comprises at least one superlattice period comprising a set of wells and a set of barriers. The thickness of at least one of the following elements: each well in the group of wells or each barrier in the group of barriers varies along a length of the p-type superlattice.US 2013 / 0 099 141 A1 describes a light emitting device comprising a p-side, an n-side and an active layer between the p-side and the n-side. The p-side includes a p-side contact, an electron blocking layer, a separate p-side confinement heterostructure (p-SCH), and a p-confinement / current spread region disposed between the p-SCH and the p-side contact. The n-side comprises an n-side contact and an n-side separate inclusion heterostructure (n-SCH). The active layer is configured to emit light in a wavelength range, wherein the p-side and the n-side have asymmetric optical transmission characteristics with respect to the wavelength range emitted by the active layer.US 6 031 858 A describes a semiconductor laser which realizes continuous oscillation in a fundamental transverse mode at a low operating voltage by transverse mode control. This semiconductor laser is fabricated by sequentially forming on a substrate of sapphire the following layers in the order: an n-type GaN contact layer, an n-type GaAlN cladding layer, an MQW active layer, a p-type GaAlN cladding layer, the laser comprising a double heterostructure comprising a ridge in the form of a stripe formed in the cladding layer, and a light-limiting layer formed in a region except for the ridge portion of the cladding layer on the double heterostructure, wherein a refractive index of the light-limiting layer is larger than that of a p-type GaAlN cladding layer.SUMMARY(Technical Problem)Here, the composition gradient layer including the composition discontinuity described above has a large ratio (ratio of transverse resistance to series resistance) between the electrical resistance (transverse resistance) in the in-plane direction and the electrical resistance (series resistance) in the vertical direction. The vertical direction corresponds to the stacking direction of the layers in the laser diode. The in-plane direction is the direction along the surface of a layer that is perpendicular to the vertical direction. In a laser diode, high longitudinal conductivity and a low ratio of transverse resistance to longitudinal resistance are simultaneously required for the cladding layer (in particular the p-type cladding layer), since a high current density must be injected uniformly over the electrode region. At the same time, the cladding layer must not have any increased internal losses, since the optical mode is absorbed in the electrodes.The present disclosure aims to provide a laser diode capable of achieving high longitudinal conductivity and low ratio of transverse to longitudinal resistance and suppressing increase in internal losses.(Solution of Problem)The above problem is solved by the subject matter of the independent claims. Examples and technical descriptions of apparatuses, products, and / or methods in the specification and / or the drawings, which are not covered by the claims, are not illustrated as embodiments of the invention, but as background or examples useful for understanding the invention. A laser diode according to an example includes an AlN single crystal substrate; an n-type cladding layer formed on the substrate and including a nitride semiconductor layer having n-type conductivity; a light emitting layer formed on the n-type cladding layer and including one or more quantum wells; a p-type cladding layer formed on the light emitting layer and including a nitride semiconductor layer having p-type conductivity; and a p-type contact layer formed on the p-type cladding layer and including a nitride semiconductor including GaN. The p-type cladding layer includes a p-type longitudinal conduction layer including Al s Ga 1-s N (0.3≤s≤1), having a composition gradient such that an Al composition s decreases as the distance from the substrate increases, and has a film thickness of less than 0.5 μm; and a p-type transverse conduction layer including AltGa 1-t N (0<t≤1). Here, the term "on" in the phrase "an n-type cladding layer formed on the substrate and comprising a nitride semiconductor layer having n-type conductivity" means that the n-type cladding layer is formed over the substrate, but also includes the case where another layer is additionally present between the substrate and the n-type cladding layer. The term "on" also has the same meaning with respect to the relationships between other layers.(Advantageous Effect)According to the present disclosure, a laser diode capable of achieving high longitudinal conductivity and low ratio of shunt to series resistance and suppressing increase in internal losses can be provided.BRIEF DESCRIPTION OF THE DRAWINGSIn the accompanying drawings: FIG. 1 is a cross-sectional view showing the configuration of a laser diode according to an embodiment.DETAILED DESCRIPTION<Konfiguration of Laser Diode>As illustrated in FIG. 1, the laser diode 1 of the present embodiment includes a substrate 11, an n-type cladding layer 12, an n-type waveguide layer 13, a light emitting layer 14, a p-type waveguide layer 15, a p-type cladding layer 20, and a p-type contact layer 18. the p-type cladding layer 20 has a p-type longitudinal guide layer 16 and a p-type transverse guide layer 17. In order to inject holes into the light emitting layer 14, the laser diode 1 includes a p-type longitudinal guide layer 16 including Al s Ga 1-s N having an Al composition s that decreases as the distance from the upper surface of the substrate 11 increases, and a p-type transverse guide layer 17, the AltGa comprises 1-t N (minimum value of t>s) on a surface adjacent to the p-type longitudinal conduction layer 16. Here, the minimum value of s refers to the smallest value of s that can be occupied by the p-type longitudinal conduction layer 16 with Al s Ga 1-s N (0.3≤s≤1) having a composition gradient. A p-type longitudinal conductive layer 16 comprising Al s Ga 1-s having such a gradient that the Al composition s decreases as the distance from the substrate 11 increases can acquire p-type conductivity. The gradient of the Al composition s generates an internal electric field toward the upper surface (for example, in the vertical direction) of the substrate 11. the p-type longitudinal conductive layer 16 therefore has a higher longitudinal conductivity than an Al s Ga 1-s- solid solution comprising a single Al composition s, and is suitable for the laser diode 1. On the other hand, since the transverse resistance in the layer having an Al composition with a gradient is much higher than the longitudinal resistance, the ratio of the transverse resistance to the longitudinal resistance tends to be larger. Here, the upper surface of the substrate 11 refers to the intersection with the directly overlying layer (the n-type cladding layer 12 in the example of FIG. 1 ) among the layers stacked on the substrate 11.(Substrate)The substrate 11 preferably has a low dislocation density in the plane, and is such that a nitride semiconductor including Al and Ga can be grown on the top surface of the substrate 11. An embodiment in which the effect of the present disclosure can be maximized is a good quality layer having an in-plane dislocation density of 5×10 4 cm -2 or less among the various layers of the laser diode 1. especially, in crystals having an in-plane dislocation density of 5×10 4 cm -2 or less, carrier scattering caused by dislocations is reduced, thereby decreasing the series resistance. This results in a further reduction in the ratio of transverse resistance to longitudinal resistance. Therefore, the substrate 11 needs to have a defect density (for example, 1×10 3 cm 2 to 1×10 4 cm 2) that is even lower than the above defect density. Among the various substrates 11, a substrate 11 with which an Al s Ga 1-s N solid solution having a defect density of 1×10 4 cm -2 or less can be obtained on an AlN single crystal substrate 11 is preferable, but this example is not limiting. The threading dislocation density of the substrate 11 can be measured, for example, by measuring the etch pit density after performing KOH-NaOH eutectic etching at 450° C. for 5 minutes.The substrate 11 includes, consists essentially of, or is composed of various materials (such as SiC, Si, MgO, Ga 2 O 3, aluminum oxide, ZnO, GaN, InN, and / or sapphire) on which an Al u Ga 1-u N material (0≤u≤1.0) can be formed, for example, by epitaxial growth. The substrate 11 may be covered with a homoepitaxial layer comprising, consisting essentially of, or being composed of the same material present in or on the substrate 11, for example AlN.Except for N, the substrate 11 may contain impurities such as other Group V elements, for example, P, As or Sb, or H, C, O, F, Mg, Si and the like, which are mixed for example to achieve conductivity, but these elements are not limiting.The laser diode 1 according to the present disclosure may be formed on a surface that is preferably, but not exclusively, a (0001) surface or a surface inclined at a certain angle (for example, -4° to 4°, preferably -0.4° to 0.4°) to the normal of the (0001) surface.The various layers of a multilayer film structure on the substrate 11 may be formed by a variety of different techniques, such as metal organic chemical vapor deposition (MOCVD), deposition techniques such as halide vapor phase epitaxy (HVPE), epitaxy methods such as molecular beam epitaxy (MBE), and the like.(P-type cladding layer)The p-type cladding layer 20 includes a nitride semiconductor layer having p-type conductivity. The p-type cladding layer 20 is preferably completely strained with respect to the substrate 11. A layer of the laser diode 1 formed to be completely strained can suppress an increase in density of threading dislocations, thereby maximizing the effects of the present disclosure. The term "fully strained with respect to the substrate 11" means that the layer constituting a part of the multilayer film has extremely low strain relaxation with respect to the substrate 11 with a lattice relaxation rate of 5% or less. The lattice relaxation rate can be given by the reciprocal lattice coordinates of the diffraction peaks of the substrate 11 and the reciprocal lattice coordinates of the diffraction peaks of one of the asymmetric planes such as the (105), (114), or (205) planes for which sufficient diffraction intensity can be obtained by X-ray diffraction measurement of the asymmetric plane.(P-type longitudinal conductive layer)The p-type longitudinal conduction layer 16 is a layer comprising Al s Ga 1-s N with such a gradient that the Al composition s decreases in a direction away from the upper surface of the substrate 11 to obtain a p-type conductivity. The layer thickness and the range of the Al composition s of the p-type longitudinal conduction layer 16 are components of a band gap that does not absorb light of the desired emission wavelength, and the Al composition and the layer thickness can be limited to increase the overlap between the intensity distribution of the electric field of the light mode stationary in the device and the light emitting layer 14 (for example, to increase the light confinement). When the emission wavelength of the light emitting layer 14 is 210 nm or more and 300 nm or less, a layer comprising Al s Ga 1-s N is preferably used so that the Al composition s decreases in a direction away from the upper surface of the substrate 11 in a range of, for example, 0.3 or more and or 1.0 less, and the film thickness is preferably 250 nm or more and 450 nm or less, more preferably 300 nm or more and 400 nm or less. By suitably controlling the film thickness, the internal loss of the laser diode 1 can be reduced.From the viewpoint of proper light confinement and formation of a p-type cladding layer under full stress, it may be advantageous that the Al composition s of the p-type longitudinal conduction layer is greater than 0.35 and 1.0 or less.The internal loss of the laser diode 1 can be measured, for example, by a known method such as the variable stripe length method (VSLM).The p-type longitudinal conductive layer 16 does not need to have a uniform change in the Al composition with respect to the layer thickness. For example, in order to increase the light confinement, a configuration may be adopted in which the variation of the Al composition decreases asymptotically or stepwise as the light emitting layer 14 approaches.For reasons such as suppression of diffusion of impurities, the p-type longitudinal line layer 16 preferably does not include impurities such as H, Mg, Be, Zn, Si or B in a region near the p-type waveguide layer 15, that is, the p-type longitudinal line layer 16 is preferably in an undoped state. The term "undoped" as used herein means that the above elements are not intentionally introduced as elements into the process of forming the target layer. This is not the case when elements in the range of 10 16 cm -3 or less, for example from raw materials or manufacturing plants, are mixed in. The amount of a mixed element can be determined by a technique such as secondary electron ion mass spectrometry. The term "undoped" has substantially the same meaning in the present application. The region of the p-type longitudinal guide layer 16 to be in an undoped state includes at least the boundary with the p-type waveguide layer 15. For example, the entire region of the longitudinal p-type conductor layer 16 may be in the undoped state. As another example, 50% of the p-type longitudinal conduction layer 16 in a region closer to the p-type waveguide layer 15 than to the transverse p-type conductor layer 17 may be in an undoped state. As another example, about 10% of the p-type longitudinal guide layer 16 in a region near the p-type waveguide layer 15 may be in an undoped state.Between the p-type longitudinal guide layer 16 and the p-type waveguide layer 15, an intermediate layer of Al v Ga 1-v N (0<v≤1.0) may be provided so that the Al composition v increases in the direction away from the upper surface of the substrate 11 to improve the conductivity, for example, and / or to form the transverse p-type guide layer 17 and the p-type contact layer 18 with complete deformation. The intermediate layer between the p-type longitudinal guide layer 16 and the p-type waveguide layer 15 may be a mixed crystal that serves as a band gap and does not absorb light of a desired emission wavelength. In addition, the intermediate layer preferably has a layer thickness of 50 nm or less, and may be undoped.For example, the series resistance of the p-type series line layer 16 may be calculated with the resistance value Rs' that results as Rs'=Rs-Rn by subtracting the resistance Rn contributed by the n-type cladding layer 12 from the series resistance Rs of the laser diode 1 in an embodiment of the present application. From the surface A of the p-type electrode in contact with the p-type contact layer 18 of the laser diode 1 and the film thickness T of the p-type cladding layer 20, the series resistance of the p-type cladding layer 20 can be calculated as Rs' × A / T. The resistance value R of the n-type cladding layer 12 can be determined by, for example, a transmission line measurement method or a non-contact resistance measurement using eddy current.(P-type cross-conduction layer)The p-type cross-conduction layer 17 may be thin to facilitate quantum transfer of carriers passing through the p-type cross-conduction layer 17. The film thickness is, for example, 20 nm or less or 10 nm or less, preferably 5 nm or less.Impurities such as H, Mg, Be, Zn, Si or B may be intentionally mixed in the p-type cross-conduction layer 17 to control, for example, the series resistance of the p-type cross-conduction layer 17. The amount of the impurities to be mixed may be, for example, 1×10 18 cm -3 to 5×10 21 cm -3 depending on the strength of the electric field induced at the surface and inside the p-type cross-conduction layer 17. The amount of the mixed impurities may also be between 1×10 19 cm -3 and 5×10 21 cm -3.The Al composition of the p-type cross-conduction layer 17 at the interface with the p-type contact layer 18 is preferably in the range of 0.9 or more to 1.0 or less, and complete deformation with respect to the substrate 11 is preferably achieved. In such a p-type cross-conduction layer 17, the net internal electric field generated at the surface and on the inner side near the surface of the p-type cross-conduction layer 17 becomes negative, thereby inducing holes, resulting in an improvement in the cross conductivity. The distribution of the Al composition of the p-type cross-conduction layer 17 in the region of the laser diode 1 is preferably limited to 5% or less. Such a p-type cross-conduction layer 17 can achieve higher cross-conductivity due to the decreased carrier scattering due to the composition distribution.The p-type cross-conduction layer 17 is preferably formed as Al t Ga 1-t N having an Al composition t of 0.9 ≤ t ≤ 1.0 by keeping Al y Ga 1-y N comprising an Al composition y smaller than the Al composition t of the final p-type cross-conduction layer 17 in a high temperature state so that the Al and Ga raw materials are not supplied.(N-type cladding layer)The n-type cladding layer 12 includes a nitride semiconductor layer having n-type conductivity. The n-conducting cladding layer 12 is preferably formed such that it is completely strained with respect to the substrate 11. In order to form the n-type cladding layer 12 so as to be completely strained with respect to the substrate 11, an intermediate layer having a uniformly varying Al composition may be present at the interface between the n-type cladding layer 12 and the substrate 11, and the Al composition and the film thickness of the n-type cladding layer 12 may be limited. The Al composition of the n-type cladding layer 12 may be limited to achieve a low contact resistance to a suitable electrode (for example, 1×10 -6 Ωcm 2 to 1×10 -3 Ωcm 2, preferably 1×10 -6 Ωcm 2 to 1×10 -4 Ωcm 2). In an embodiment of the n-type cladding layer 12, the Al composition may be 0.6 to 0.8 and the thickness may be 0.3 μm to 0.5 μm in consideration of the above limitations.The n-type cladding layer 12 may be a graded layer such that the Al composition increases in a direction away from the substrate 11 for purposes such as controlling the longitudinal conductivity thereof. In this case, the aforementioned limitation of the Al composition can be similarly represented as an Al composition obtained by averaging the Al composition at each position in the layer thickness direction in the n-type cladding layer over the layer thickness of the n-type cladding layer 12.Other than N, the n-type cladding layer 12 may be incorporated with impurities such as Group V elements other than N, for example, P, As or Sb, or H, C, O, F, Mg, Ge, Si and the like to control, for example, the longitudinal conductivity of the layer, but these elements are not limitative. The appropriate amount of the impurity mixed is limited by the Al composition of the n-type cladding layer 12. The amount is preferably 1×10 19 cm -3 to 1×10 20 cm -3.(Waveguide layer)The waveguide layer is a nitride semiconductor comprising Al and Ga having a band gap which does not absorb light of the desired emission wavelength, and the Al composition and film thickness can be limited to increase the overlap between the electric field intensity distribution of light stationary in the device and the light emitting layer 14. For example, in the case of a light-emitting layer 14 having a wavelength of 260 nm to 280 nm, the Al composition is preferably 0.55 to 0.65, and the layer thickness is preferably 70 nm to 150 nm.The waveguide layer may be composed of two layers: a part (n-type waveguide layer 13) on the n-type cladding layer 12 side of the light emitting layer 14 and a part (p-type waveguide layer 15) on the p-type cladding layer 20 side of the light emitting layer 14. The p-type waveguide layer 15 may be formed between the p-type cladding layer 20 and the light emitting layer 14. The film thickness ratio of the n-type waveguide layer 13 and the p-type waveguide layer 15 may be various values depending on the light inclusion in the light emitting layer 14 and the Al composition of the n-type cladding layer 12 and the p-type cladding layer 20. The Al composition of the p-type waveguide layer 15 may be higher than the Al composition of the n-type waveguide layer 13 to avoid light absorption in the metal present on the p-type contacts. For the same reason, the layer thickness of the p-type waveguide layer 15 may be greater than the layer thickness of the n-type waveguide. Except for N, the n-type waveguide layer 13 may contain impurities such as V group elements other than N, for example, P, As, or Sb or H, C, O, F, Mg, Si, and the like, for example, to achieve the same conductivity as the n-type cladding layer 12, but these elements are not limiting.A composition gradient layer comprising Al w Ga 1-w N such that the Al composition w decreases in the direction away from the upper surface of the substrate 11 may be provided between the n-type waveguide layer 13 and the n-type cladding layer 12 for purposes such as improving the longitudinal conductivity. The intermediate layer between the n-type waveguide layer 13 and the n-type cladding layer 12 preferably has a layer thickness of 10 nm or less.A graded composition layer comprising Al x Ga 1-x N such that the Al composition x increases in the direction away from the upper surface of the substrate 11 may be provided between the p-type waveguide layer 15 and the p-type cladding layer 20 for purposes such as improving the longitudinal conductivity. The intermediate layer between the p-type waveguide layer 15 and the p-type cladding layer 20 preferably has a sufficiently small layer thickness (for example, 30 nm or less, or 20 nm or less) so as not to impair light confinement in the waveguide layer.An electron blocking layer having a band gap larger than that of the p-type waveguide layer 15 may be provided within the p-type waveguide layer 15, between the p-type waveguide layer 15 and the light emitting layer 14, between the p-type waveguide layer 15 and the p-type longitudinal guide layer 16, or in a part of the p-type waveguide layer 15. The electron blocking layer may be 30 nm or less, 20 nm or less, preferably 15 nm or less, in order to facilitate the penetration of holes into the electron blocking layer.(Light-Emitting Layer)The light emitting layer 14 may include a single quantum well or multiple quantum wells disposed between the n-type waveguide layer 13 and the p-type waveguide layer 15. The number of quantum wells may be 3, 2 or 1, depending on the longitudinal conductivity of the n-type cladding and the p-type cladding.For example, in order to reduce the effect of crystal defects in the light emitting layer 14, all or part of the light emitting layer 14 may be intentionally mixed with elements such as Si, Sb, P, or the like in an amount of 1×10 -15 cm -3 or more.(P-type contact layer)The p-type contact layer 18 may be formed on the p-type cladding layer 20 and may be a nitride semiconductor including GaN. Except for N, the p-type contact layer 18 may contain impurities such as V group elements other than N, for example, P, As, or Sb, or H, C, O, F, Mg, Ge, Si, and the like to reduce the contact resistance, but these elements are not limited. For example, 1×10 20 cm -3 to 1×10 22 cm -3 Mg may be mixed.The electrical contact to the laser diode 1 of the present disclosure may be made by an electrode layer disposed on the p-contact layer 18 and an electrode layer disposed in contact with the n-cladding layer 12. For example, an electrode layer may be disposed on the back surface of the substrate 11. Alternatively, in one or more regions near the p-type contact layer 18, various upper layers of the laser diode 1 may be removed by, for example, chemical etching or dry etching to expose the n-type cladding layer 12, and an electrode may be disposed on the exposed n-type cladding layer 12.(Electrode Layer)The electrode layer disposed on the p-type contact layer 18 may be made of a metal including Ni, Pt, Au, B and / or Pd.The n-type cladding layer 12 or the electrode layer disposed on the back surface of the substrate 11 may be a metal comprising V, Al, Au, Ti, Ni and / or Mo. The metal layer in contact with the substrate 11 is preferably a metal comprising V or Ti.EXAMPLESThe laser diode 1 of Examples 1 to 4 was fabricated to have the same layer structure as the laser diode 1 of the above embodiment. Examples 5 and 6, Comparative Examples 1 and 2, and Reference Examples 1 to 5 are also shown below.[Example 1]As Example 1, the nitride semiconductor laser diode 1 depicted below was fabricated. For manufacturing the laser diode 1, MOCVD was used, and as raw materials, trimethylgallium (TMG), triethylgallium (TEG), trimethylaluminium (TMA), ammonia (NH 3), silane (SiH 4) and biscyclopentadienylmagnesium (CpMg 2) were used. A 0.2 m μ thick homoepitaxial layer comprising AlN was formed by reacting TMA and NH 3 in an H atmosphere 2 at 1200° C. on a surface inclined by 0.1° to 0.3° relative to the

[0001] plane of an AlN single crystal substrate 11.An AlGaN intermediate layer having a film thickness of 30 nm and an Al composition decreasing uniformly from 1.0 to 0.7 in the direction away from the upper surface of the substrate 11 and an n-type cladding layer 12 made of Al 0.7 Ga 0.3 N having a film thickness of 0.35 μm and doped with 5 cm×10 19-3 Si were stacked in this order on a homoepitaxial layer comprising AlN by reacting TMA, TMG, NH 3 and SiH 4 in an H atmosphere 2 at 1055 C°. The homoepitaxial AlN layer, the intermediate layer and the n-type cladding layer 12 were formed so as to be completely deformed with respect to the substrate 11 by being formed at a speed of 0.3 μm / h to 0.6 μm / h.An n-type waveguide layer 13 having a film thickness of 60 nm and comprising Al 0,63 Ga 0,37 N and a light emitting layer 14 comprising a multilayer quantum well layer having a total thickness of 30 nm were stacked on the n-type cladding layer 12 in this order by reacting TMA, TMG and NH 3 in an H atmosphere 2 at 1055° C. During the formation of a part of the barrier layer of the light emitting layer 14, the light emitting layer was doped with 3×10 19 cm -3 of Si by incorporating SiH 4 as a raw material. Further, on the light emitting layer 14, a p-type waveguide layer 15 having a layer thickness of 50 nm and comprising Al 0.62 Ga 0.38 N was formed. The n-type waveguide layer 13, the light emitting layer 14, and the p-type waveguide layer 15 were formed to be completely deformed with respect to the substrate 11 by being formed at a speed of 0.4 μm / hr.An AlGaN intermediate layer having a film thickness of 20 nm and an Al composition uniformly increasing from 0.62 to 1.0 in the direction away from the upper surface of the substrate 11 and a p-type longitudinal guide layer 16 having a film thickness of 0.32 μm and an Al composition decreasing from 1.0 to 0.3 in the direction away from the upper surface of the substrate 11 were stacked on the p-type waveguide layer 15 in this order by reacting TMA, TMG and NH 3 in an H atmosphere 2 at 1055 C°. The longitudinal p-type conductor layer 16 was formed to be completely deformed with respect to the substrate 11 by being formed at a speed of 0.3 μm / h to 0.5 μm / h. The entire region of the p-type longitudinal conductive layer 16 was in an undoped state.On the p-type longitudinal wiring layer 16, a p-type transverse wiring layer 17 having a layer thickness of 3 nm and comprising Al 0.45 Ga 0.05 N was formed. In addition, the supply of TMA and TMG materials was stopped at 1055 C° and a state in which only CpMg 2 was supplied was maintained for 10 minutes or longer (annealing) to convert the p-type cross-conduction layer 17 into an Al 0.97 Ga 0.03 N layer doped with 1×10 20 cm -3 Mg. By this conversion method, the p-type interconnection layer 17 was formed so as to be completely strained with respect to the substrate 11.The XRD measurement of the (002) plane revealed that the dispersion of the Al composition of the p-type cross conduction layer 17 in the region corresponding to the region of the laser diode 1 was 3.5%. Confirmation of atomic arrangement by means of transmission images in the <11-20> direction of a transmission electron microscope at multiple locations revealed that the p-type cross-conduction layer 17 was completely strained with respect to the substrate 11.A p-type contact layer 18 having a layer thickness of 20 nm and comprising GaN doped with 5×10 20 cm -3 Mg was formed on the p-type cross-conduction layer 17 by reaction of TMG, CpMg 2 and NH 3 in an H atmosphere 2 at 9407 C.In the nitride semiconductor laser diode 1 fabricated as described above, the resistance of the p-type layer was further reduced by annealing at 700 C° for 10 minutes or longer in an N atmosphere 2. By dry etching with a gas comprising Cl 2 the n-type cladding layer 12 was exposed in a rectangular region parallel to <11-20> direction and stretched in <11-20> direction. In addition, a passivation layer including SiO 2 was formed on the surface of the nitride semiconductor laser diode 1.A plurality of rectangular electrode metal regions (p-type electrodes) including Ni or Au which are parallel to the <11-20> direction and elongated in the <11-20> direction were formed on the p-type contact layer 18. A plurality of rectangular electrode metals (n-type electrodes) including V, Al, Ni, Ti or Au, which are parallel to the <11-20> direction and extend in the <11-20> direction, were formed in the region where the n-type cladding layer 12 was exposed. In addition, the substrate 11 was divided into stripes within the electrode metal region by multiple columns parallel to the <1-100> direction.Resonators of length Yμm (Y = 50, 100, 150, 200, 250, 300, 350, 400μm) were formed with a plurality of natural cleavage planes parallel to the <1-100> direction as end faces and with the long edges perpendicular to the cleavage direction. Using these resonators with different lengths Y μm, the dependence of the excitation length was determined with rectangular laser spots of a length of 500 μm and a width of 15 μm. Calculations based on VSLM revealed that the internal loss is 10 cm -1.For the laser diode 1 manufactured as described above, the total series resistance of the laser diode 1 was measured by evaluating the forward voltage characteristic with the nearest p-type and n-type electrodes. Moreover, by measuring the resistance between a plurality of n-type electrodes based on the TLM method, the longitudinal and transverse resistances of the n-type cladding layer 12 were obtained. Since the n-type cladding layer 12 is a homogeneous mixed crystal, the longitudinal and transverse resistances coincide. From the above measurement data, the longitudinal conductivity of the p-type cladding layer 20 was calculated to be 0.13 Ω -1 cm -1. In addition, by measuring the resistance between a plurality of p-type electrodes based on the TLM method, the transverse resistance of the p-type cladding layer 20 was obtained. The ratio of the transverse resistance to the longitudinal resistance of the p-type cladding layer 20 was 1.5.The lattice relaxation rates calculated from the XRD diffraction intensity peaks in the (205) plane of the substrate 11 and the XRD diffraction intensity peaks in the (205) plane of each film of the laser diode 1 manufactured as described above were all less than 4%.[Example 2]A laser diode 1 was fabricated by a similar method as in Example 1, except that the film thickness of the p-type longitudinal conduction layer 16 was set to 0.21 μm.For the laser diode 1 manufactured as described above, the lattice relaxation rate calculated by the method described in Example 1 was 4% or less.The longitudinal conductivity of the p-type cladding layer 20 was 0.17 Ω -1 cm -1, calculated by the method described in Example 1. The ratio of the transverse resistance to the longitudinal resistance of the p-type cladding layer 20 was 1.9 calculated by the method described in Example 1. The internal loss by VSLM was 20 cm -1, as measured by the method described in Example 1.[Example 3]A laser diode 1 was fabricated by a similar method as in Example 1, except that the film thickness of the p-type longitudinal conduction layer 16 was set to 0.25 μm.For the laser diode 1 fabricated as described above, the lattice relaxation rates calculated by the method described in Example 1 were all 4% or less.The longitudinal conductivity of the p-type cladding layer 20 was 0.15 Ω -1 cm -1, calculated by the method described in Example 1. The ratio of the transverse resistance to the longitudinal resistance of the p-type cladding layer 20 was 1.9 calculated by the method described in Example 1. The internal loss by VSLM was 15 cm -1, as measured by the method described in Example 1.[Example 4]A laser diode 1 was fabricated by a similar method as in Example 1, except that the film thickness of the p-type longitudinal conduction layer 16 was set to 0.45 μm.For the laser diode 1 fabricated as described above, the lattice relaxation rates calculated by the method described in Example 1 were all 4% or less.The longitudinal conductivity of the p-type cladding layer 20 was 0.11 Ω -1 cm -1, calculated by the method described in Example 1. The ratio of the transverse resistance to the longitudinal resistance of the p-type cladding layer 20 was 1.4 calculated by the method described in Example 1. The internal loss by VSLM was 9 cm -1, as measured by the method described in Example 1.[Example 5]A laser diode 1 was produced by a similar method to that of Example 1 except for the method of producing a p-type cross-conduction layer 17 described below.A p-type transverse conduction layer 17 having a film thickness of 3 nm and comprising Al 0,97 Ga 0,03 N doped with 3×10 20 cm -3 Mg was formed on the p-type longitudinal conduction layer 16 by reacting TMA, TMG, Cp 2 Mg and NH 3 in an H atmosphere 2 at 940° C. in a similar manner to the various layers of the laser diode 1.For the laser diode 1 fabricated as described above, the lattice relaxation rates calculated by the method described in Example 1 were all 4% or less.The longitudinal conductivity of the p-type cladding layer 20 was 0.13 Ω -1 cm -1, calculated by the method described in Example 1. The ratio of the transverse resistance to the longitudinal resistance of the p-type cladding layer 20 was 2.9 calculated by the method described in Example 1. The internal loss by VSLM was 11 cm -1, as measured by the method described in Example 1.[Example 6]A laser diode 1 was fabricated by a similar method as in Example 1, except that the Mg concentration in the p-type cross-conduction layer 17 was set to 1×10 16 cm -3.For the laser diode 1 fabricated as described above, the lattice relaxation rates calculated by the method described in Example 1 were all 4% or less.The longitudinal conductivity of the p-type cladding layer 20 was 0.11 Ω -1 cm -1, calculated by the method described in Example 1. The ratio of the transverse resistance to the longitudinal resistance of the p-type cladding layer 20 was 1.6 calculated by the method described in Example 1. The internal loss by VSLM was 10 cm -1, as measured by the method described in Example 1.[Comparative Example 1]A laser diode 1 identical to that of Example 1 was fabricated except that the p-type longitudinal conduction layer 16 is made of Al 0.7 Ga 0.3 N (no composition gradient) having a layer thickness of 0.32 μm.For the laser diode 1 fabricated as described above, the lattice relaxation rates calculated by the method described in Example 1 were all 4% or less.For the laser diode 1 fabricated as described above, the longitudinal conductivity of the p-type cladding layer 20 was 0.06 Ω -1 cm -1, calculated by the method described in Example 1. The ratio of the transverse resistance to the longitudinal resistance of the p-type cladding layer 20 was 11.3 calculated by the method described in Example 1. The internal loss by VSLM was 31 cm -1, as measured by the method described in Example 1.[Comparative Example 2]A laser diode 1 having no p-type shunt line layer 17 was fabricated by setting the p-type shunt line layer 16 in Example 1 to Al 0,7 Ga 0,3 N (no composition gradient) having a layer thickness of 0.32 μm, and after forming the p-type shunt line layer 16, the procedures from the formation of the p-type contact layer 18 were performed.For the laser diode 1 fabricated as described above, the lattice relaxation rates calculated by the method described in Example 1 were all 4% or less.For the laser diode 1 fabricated as described above, the longitudinal conductivity of the p-type cladding layer 20 was 0.07 Ω -1 cm -1, calculated by the method described in Example 1. The ratio of the transverse resistance to the longitudinal resistance of the p-type cladding layer 20 was 16.4 calculated by the method described in Example 1. The internal loss by VSLM was 31 cm -1, as measured by the method described in Example 1.[Reference Example 1]A laser diode 1 having no p-type shunt line layer 17 was fabricated by performing a similar process as in Example 1 up to the fabrication of the p-type longitudinal line layer 16 and then the process from the formation of the p-type contact layer 18.For the laser diode 1 fabricated as described above, the lattice relaxation rates calculated by the method described in Example 1 were all 4% or less.For the laser diode 1 fabricated as described above, the longitudinal conductivity of the p-type cladding layer 20 was 0.14 Ω -1 cm -1, calculated by the method described in Example 1. The transverse to longitudinal resistance ratio of the p-type cladding layer 20 was 26.7 as calculated by the method described in Example 1. The internal loss by VSLM was 10 cm -1, as measured by the method described in Example 1.[Reference Example 2]In order to intentionally stress relief the structure of the laser diode, a laser diode 1 was fabricated by a similar method as in Example 1, except that the film thickness of the p-type longitudinal conduction layer 16 was set to 0.8 μm.For the laser diode 1 fabricated as described above, the lattice relaxation rates calculated by the method described in Example 1 were all 30%.For the laser diode 1 fabricated as described above, the longitudinal conductivity of the p-type cladding layer 20 was 0.02 Ω -1 cm -1, calculated by the method described in Example 1. The ratio of the transverse resistance to the longitudinal resistance of the p-type cladding layer 20 was 6.1 calculated by the method described in Example 1. The internal loss by VSLM was 17 cm -1, as measured by the method described in Example 1.[Reference Example 3]A laser diode 1 was fabricated by a similar method as in Example 1, except that the film thickness of the p-type longitudinal conduction layer 16 was set to 0.5 μm.For the laser diode 1 fabricated as described above, the lattice relaxation rates calculated by the method described in Example 1 were all 20%.For the laser diode 1 fabricated as described above, the longitudinal conductivity of the p-type cladding layer 20 was 0.04 Ω -1 cm -1, calculated by the method described in Example 1. The ratio of the transverse resistance to the longitudinal resistance of the p-type cladding layer 20 was 9.7 calculated by the method described in Example 1. The internal loss by VSLM was 8 cm -1, as measured by the method described in Example 1.[Reference Example 4]A laser diode 1 was fabricated by the same method as in Example 1, except that the p-type longitudinal conduction layer 16 had a thickness of 0.32 μm and was stacked so that the Al composition decreased from 1.0 to 0.1 in the direction away from the upper surface of the substrate 11.For the laser diode 1 fabricated as described above, the lattice relaxation rates calculated by the method described in Example 1 were all 4% or less.For the laser diode 1 fabricated as described above, the longitudinal conductivity of the p-type cladding layer 20 was 0.13 Ω -1 cm -1, calculated by the method described in Example 1. The ratio of the transverse resistance to the longitudinal resistance of the p-type cladding layer 20 was 1.5 as calculated by the method described in Example 1. The internal loss by VSLM was 27 cm -1, as measured by the method described in Example 1.[Reference Example 5]A laser diode 1 was fabricated by the same method as in Example 1, except that the p-type longitudinal conduction layer 16 had a thickness of 0.32 μm and was stacked so that the Al composition decreased from 1.0 to 0.2 in the direction away from the upper surface of the substrate 11.For the laser diode 1 fabricated as described above, the lattice relaxation rates calculated by the method described in Example 1 were all 4% or less.For the laser diode 1 fabricated as described above, the longitudinal conductivity of the p-type cladding layer 20 was 0.13 Ω -1 cm -1, calculated by the method described in Example 1. The ratio of the transverse resistance to the longitudinal resistance of the p-type cladding layer 20 was 1.5 as calculated by the method described in Example 1. The internal loss by VSLM was 19 cm -1, as measured by the method described in Example 1.The above-described configurations, manufacturing conditions, and evaluation results for the laser diodes 1 of Examples 1 to 6, Comparative Examples 1 and 2, and Reference Examples 1 to 5 are summarized in the following Table 1. [Table 1] Table 1] [Table 1] Table 1]Example 11.0 / 0.30,320,973Annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing1×10 20cm -34% or less100,131,5Example 21.0 / 0.30,210,973Annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing1×10 20cm -34% or less200,171,9Example 31.0 / 0.30,250,973Annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing1×10 20cm -34% or less150,151.9Example 41.0 / 0.30,450,973Annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing1×10 20cm -34% or less90,111,4Example 51.0 / 0.30,320,973stack stacks stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack stack3×10 20cm -34% or less110,132,9Example 61.0 / 0.30,320,973Annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing1×10 19 cm -34% or less100,111,6Comparative Example 10.7 / 0.7 (No composition gradient)0,320,973Annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing1×10 20 cm 34% or less310,0611,3Comparative Example 20.7 / 0.7 (No composition gradient)0,32--N / A (no film formed)-4% or less310,0716,4Reference Example 11.0 / 0.30,32--N / A (no film formed)-4% or less100,1426,7Reference Example 21.0 / 0.30,80,973Annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing1×10 20cm -330%170,026,1Reference Example 31.0 / 0.30,50,973Annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing1×10 20cm -320%80,049,7Reference Example 41.0 / 0.10,320,973Annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing1×10 20cm -34% or less270,131,5Reference Example 11.0 / 0.20,320,973Annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing annealing1×10 20cm -34% or less190,131,5(Comparison)The laser diodes 1 of Examples 1 to 6 have a longitudinal conductivity of 0.11 or more and 0.17 or less, a ratio of transverse resistance to longitudinal resistance of 1.5 or more and 2.9 or less, and an internal loss of 9 cm -1 or more and 20 cm -1 or less. The laser diodes 1 of Comparative Examples 1, 2 have a longitudinal conductivity of 0.06 or more and 0.07 or less, a ratio of transverse resistance to longitudinal resistance of 11.3 or more and 16.7 or less, and an internal loss of 31 cm -1.The laser diodes 1 of Comparative Examples 1, 2 have a structure that does not use a composition gradient layer as the p-type longitudinal conduction layer 16. Therefore, the longitudinal conductivity is low. Moreover, in Comparative Example 2, the resistance ratio is further increased compared to Comparative Example 1 because of the absence of the p-type cross conduction layer 17. None of the comparative examples can achieve properties that simultaneously exhibit the low internal loss, high longitudinal conductivity, and low ratio of shunt to series resistance as exhibited by the laser diode 1 of Examples 1 to 6.Furthermore, the laser diode s1 of Reference Examples 1 to 5 is to be examined. The laser diode 1 of Reference Example 1 comprises a composition gradient layer as a p-type shunt layer as in Comparative Example 1 but does not have a p-type shunt layer 17. the laser diode 1 of Reference Example 1 cannot achieve a low ratio of shunt resistance to series resistance as compared with Examples 1 to 6. The laser diodes 1 of Reference Examples 2 and 3 contain, as the p-type longitudinal conduction layer 16, a composition gradient layer as in Comparative Example 1, but the layer thickness of the p-type longitudinal conduction layer 16 is 0.5 μm or more. The laser diodes 1 of Reference Examples 2 and 3 cannot achieve high longitudinal conductivity or low ratio of transverse resistance to longitudinal resistance compared with Examples 1 to 6. The laser diodes 1 of Reference Examples 4 and 5 contain a composition gradient layer as a p-type longitudinal conduction layer, but the minimum value of the Al composition is less than 0.3. The laser diodes 1 of Reference Examples 4 and 5 cannot achieve low internal losses as compared with Examples 1 to 6. The laser diodes 1 of Reference Examples 1 to 5 cannot be said to have characteristics having low internal loss, high longitudinal conductivity, and a low ratio of shunt to series resistance at the same time, as compared with Examples 1 to 6.(Variation)As described above, each laser diode 1 of Examples 1 to 6 has a low internal loss, a high longitudinal conductivity and, at the same time, a low ratio of transverse resistance to longitudinal resistance. In order to further examine the relationship with the oscillation, the oscillation state was measured using variants in which the configuration of the quantum well layer included in the light emitting layer 14 and the configuration of the p-type longitudinal conduction layer 16 were changed in comparison with Example 1. In the production of the variants below, a laser diode 1 was first cut with an electrode along the <11-20> direction in order to form a 400 μm long laser cavity. After an atomically flat (1-100) facet was obtained by cleavage, a highly reflective coating (90% or more reflectivity) composed of an HfO 2 / SiO 2- multilayer film was applied to both sides of the cleaved surfaces. The electrical characteristics were measured at room temperature under 50 ns pulse current injection with a period of 0.5 ms (duty cycle 0.01 %).[Variant 1]As Variant 1, a laser diode 1 having a similar configuration to that of Example 1 was produced, except that the light-emitting layer 14 contained a single quantum well layer having a total layer thickness of 7.5 nm. The laser diode 1 of Variation 1 oscillated and had an oscillation threshold of 60 kA / cm 2.[Variant 2]As Variant 2, a laser diode 1 having a similar configuration to that of Example 1 was produced, except that the light-emitting layer 14 comprises a single quantum well layer having a total layer thickness of 9 nm. The laser diode 1 of Variation 2 oscillated and had an oscillation threshold of 25 kA / cm 2.[Variant 3]As Variant 3, a laser diode 1 having a similar configuration to that of Example 1 was produced, except that the light-emitting layer 14 comprises a single quantum well layer having a total layer thickness of 15 nm. The laser diode of the 1 variation oscillated 3 and had an oscillation threshold of 9 kA / cm 2.[Variant 4]As Variant 4, a laser diode 1 having a similar configuration to that of Example 1 was produced, except that the light emitting layer 14 contained a single quantum well layer having a total layer thickness of 9 nm and a portion of the p-type longitudinal conduction layer 16 from the interface with the p-type waveguide layer 15 to 10 nm in the thickness direction was in an undoped state. Here, the portion of the p-type conductive layer 16 that was not in the undoped state was doped with 1.3×10 19 cm -3 Mg. The film thickness of the p-type longitudinal conductive film 16 was 0.32 μm as in Example 1. The laser diode 1 of the variation 4 oscillated and had an oscillation threshold of 30 kA / cm 2.[Variant 5]As Variant 5, a laser diode 1 having a similar configuration to that of Example 1 was produced, except that the light emitting layer 14 contained a single quantum well layer having a total layer thickness of 9 nm and a portion of the p-type longitudinal conduction layer 16 from the interface with the p-type waveguide layer 15 to 50 nm in the thickness direction was in an undoped state. Here, the non-undoped portion of the p-type conductive layer 16 was doped with 1.3×10 19 cm -3 Mg. The laser diode 1 of Variation 5 oscillated and had an oscillation threshold of 20 kA / cm 2.[Variant 6]As Variant 6, a laser diode 1 having a similar configuration to that of Example 1 was produced, except that the light emitting layer 14 contained a single quantum well layer having a total layer thickness of 9 nm and a portion of the p-type longitudinal conduction layer 16 from the interface with the p-type waveguide layer 15 to 100 nm in the thickness direction was in an undoped state. Here, the portion of the p-type conductive layer 16 that was not in the undoped state was doped with 1.3×10 19 cm -3 Mg. The laser diode 1 of Variation 6 oscillated and had an oscillation threshold of 18 kA / cm 2.The above-described configurations and evaluation results for the laser diodes 1 of Variations 1 to 6 are summarized in the following Table 2. [Table 2] [Table 2]Variation 17.51 LayerTotal area0.3260Variation 29.01 LayerTotal area0.3225Variation 315.01 LayerTotal area0.329Variation 49.01 Layer100.3230Variation 59.01 Layer500.3220Variation 69.01 Layer1000.3218The laser diodes 1 of the variants 1 to 6 oscillate with a low oscillation threshold. The oscillation threshold of variant 3 is, for example, 9 kA / cm 2.In the manufacture of the laser diode 1, convex hexagonal pyramidal hills (HPH) sometimes formed after the epitaxial growth, which deteriorated the characteristics of the laser diode 1. The HPH density was 6×10 3 cm -2, for example, and deterioration of the characteristics was observed by the emission peak of the wavelength shifted toward a longer wavelength. It is considered that HPHs are mainly formed in the vicinity of threading dislocations in the AlN single crystal substrate. In the laser diodes 1 of the variations, contact between the HPHs and the p-type electrode was avoided and laser oscillation was achieved by suppressing generation of threading dislocations.(Others)The present disclosure is not limited to the above-mentioned embodiments and examples. A person skilled in the art could modify the design of each embodiment, and such modified embodiments are included within the scope of the present disclosure.REFERENCE CHARACTER LIST1 Laser diode 11 Substrate 12 N-type cladding layer 13 N-type waveguide layer 14 Light emitting layer 15 P-type waveguide layer 16 P-type longitudinal line layer 17 P-type transverse line layer 18 P-type contact layer 20 P-type cladding layer

Claims

A laser diode (1) comprising: an AlN single crystal substrate (11); an n-type cladding layer (12) formed on the substrate (11) and comprising a nitride semiconductor layer having n-type conductivity; a light emitting layer (14) formed on the n-type cladding layer (12) and comprising one or more quantum wells; a p-type cladding layer (20) formed on the light emitting layer (14) and comprising a nitride semiconductor layer having p-type conductivity; and a p-type contact layer (18) formed on the p-type cladding layer (20) and comprising a nitride semiconductor comprising GaN; wherein the p-type cladding layer (20) comprises a p-type longitudinal conduction layer (16) comprising Al s Ga s1-s N (0.3 ≤ s ≤ 1), having a composition gradient such that the Al composition s decreases with increasing distance from the substrate (11), and having a film thickness of less than 0.5 μm; and a p-type transverse conduction layer (17) comprising Al t Ga 1-t N (0.3 < t ≤ 1), wherein, at a surface of the p-type transverse conduction layer (17) adjacent to the p-type longitudinal conduction layer (16), the Al composition t is greater than a minimum value of the Al composition s.The laser diode (1) according to claim 1, wherein the p-type cladding layer (20) comprises Al s Ga 1-s N (0.35 < s ≤ 1).The laser diode (1) according to claim 1 or 2, wherein the p-type cross-conduction layer (17) has a layer thickness of 20 nm or less.The laser diode (1) according to any one of claims 1 to 3, further comprising: an n-type waveguide layer (13) formed between the n-type cladding layer (12) and the light emitting layer (14) and configured to include light in the light emitting layer (14); and a p-type waveguide layer (15) formed between the p-type cladding layer (20) and the light emitting layer (14) and configured to include light in the light emitting layer (14).The laser diode (1) according to claim 4, further comprising an intermediate layer formed between the p-type longitudinal guide layer (16) and the p-type waveguide layer (15), comprising Al v Ga 1-v N (0 < v ≤ 1.0), and having such a composition gradient that an Al composition v increases as the distance from the substrate (11) increases.The laser diode (1) according to claim 4 or 5, wherein the p-type longitudinal guide layer (16) is undoped in a region including an interface with the p-type waveguide layer (15).The laser diode (1) according to any one of claims 1 to 6, wherein the emission wavelength of the light emitting layer (14) is 210 nm or more and 300 nm or less.The laser diode (1) according to any one of claims 1 to 7, wherein a film thickness of the p-type longitudinal conduction layer (16) is 250 nm or more and 450 nm or less.Laser diode (1) according to any of claims 1 to 8, wherein the p-type longitudinal conduction layer (16) and the p-type transverse conduction layer (17) are fully strained with respect to the substrate (11).

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