Nitride semiconductor laminate, method for manufacturing nitride semiconductor element, and nitride semiconductor element

Abstract

In a nitride semiconductor element, deterioration of a cladding layer is suppressed, and carrier injection efficiency is improved. A nitride semiconductor laminate forming a nitride semiconductor element is obtained by forming a first conductivity type cladding layer including a nitride semiconductor of a first conductivity type on an Al-containing nitride semiconductor substrate, forming a light-emitting layer from a nitride semiconductor including one or more quantum wells on the first conductivity type cladding layer, and forming a second conductivity type cladding layer on the light-emitting layer. Forming a part of a second conductivity type cladding layer containing a nitride semiconductor of a second conductivity type under the conditions that the wafer temperature is 900 DEG C to 1000 DEG C (inclusive) and the reactor pressure is 15 mbar to 350 mbar (inclusive); and forming a semiconductor laminated part on the nitride semiconductor substrate by forming the remainder of the second conductivity-type cladding layer under the conditions that the wafer temperature is 1030 DEG C to 1100 DEG C inclusive and the reactor pressure is 15 mbar to 350 mbar inclusive.

Description

Technical Field

[0001] This disclosure relates to a method for manufacturing a nitride semiconductor laminate and a nitride semiconductor device, as well as the nitride semiconductor device itself. Background Technology

[0002] Conventionally, nitride semiconductors have been used as materials for forming light-emitting diodes (LEDs) and laser diodes (LDs). Nitride semiconductors exhibit a direct recombination mechanism, making them suitable as materials for LEDs and LDs due to their ability to achieve high recombination efficiency and high optical gain. As an example of a laser diode using such a nitride semiconductor, a technique for oscillating a current-injection type laser diode in the ultraviolet region has been disclosed (e.g., Non-Patent Document 1).

[0003] Existing technical documents

[0004] Non-patent literature

[0005] Non-patent literature 1: Zhang et al., Applied Physics Express 12, 124003 (2019) Summary of the Invention

[0006] The problem that the invention aims to solve

[0007] While the aforementioned nitride semiconductor devices, such as laser diodes, can improve the injection efficiency of charge carriers (electrons or holes), the degradation of the coating layer is not sufficiently suppressed.

[0008] The purpose of this disclosure is to provide a method for manufacturing a nitride semiconductor laminate and a nitride semiconductor device that can simultaneously suppress the degradation of the cladding layer and improve the carrier injection efficiency, as well as the nitride semiconductor device itself.

[0009] means for solving problems

[0010] To address the aforementioned problems, in one embodiment of the method for manufacturing a nitride semiconductor stack disclosed herein, a first conductivity type cladding layer comprising a nitride semiconductor of a first conductivity type is formed on an Al-containing nitride semiconductor substrate. A light-emitting layer is formed on the first conductivity type cladding layer by a nitride semiconductor comprising one or more quantum wells. A portion of a second conductivity type cladding layer comprising a nitride semiconductor of a second conductivity type is formed under conditions of a wafer temperature of 900°C or higher and 1000°C or lower, and a reactor pressure of 15 mbar or higher and 350 mbar or lower. The remaining portion of the second conductivity type cladding layer is formed under conditions of a wafer temperature of 1030°C or higher and 1100°C or lower, and a reactor pressure of 15 mbar or higher and 350 mbar or lower, thereby forming a semiconductor stack on the nitride semiconductor substrate.

[0011] In another aspect of the manufacturing method of the nitride semiconductor device disclosed herein, after the semiconductor stack is formed by the above-described manufacturing method of the nitride semiconductor stack, unwanted portions of each layer of the semiconductor stack are removed by etching, electrodes are formed on the semiconductor stack, and the nitride semiconductor substrate on which each layer of the semiconductor stack is formed is divided into single pieces by cutting.

[0012] Furthermore, another aspect of the nitride semiconductor device disclosed herein includes an Al-containing nitride semiconductor substrate and a semiconductor stack disposed on the nitride semiconductor substrate. The semiconductor stack includes: a first conductivity type cladding layer comprising a first conductivity type nitride semiconductor; a light-emitting layer disposed on the first conductivity type cladding layer and formed of a nitride semiconductor comprising one or more quantum wells; and a second conductivity type cladding layer disposed on the light-emitting layer and formed of a second conductivity type Al-containing nitride semiconductor. The surface of the second conductivity type cladding layer has a vortex-shaped stepped structure with platforms and height differences, other than a straight line when viewed from above.

[0013] It should be noted that the above description of the invention does not list all the features of the invention disclosed herein.

[0014] Invention Effects

[0015] According to this disclosure, a method for manufacturing a nitride semiconductor stack and a nitride semiconductor device that can simultaneously suppress the degradation of the cladding layer and improve the carrier injection efficiency can be provided, as well as the nitride semiconductor device itself. Attached Figure Description

[0016] Figure 1 This is a diagram illustrating a configuration example of the Al composition in a nitride semiconductor device according to an embodiment of the present disclosure.

[0017] Figure 2A This is an AFM photograph showing the structure of the upper surface of the second conductivity type cladding layer of a nitride semiconductor device according to an embodiment of the present disclosure.

[0018] Figure 2B This is an SEM image showing the structure of the upper surface of the second conductivity type cladding layer of a nitride semiconductor device according to an embodiment of the present disclosure.

[0019] Figure 3 This is an AFM photograph showing the structure of the upper surface of the second conductivity type cladding layer of a conventional nitride semiconductor device.

[0020] Figure 4 This is a plan view illustrating a configuration example of a nitride semiconductor device according to an embodiment of the present disclosure.

[0021] Figure 5 This is a cross-sectional schematic diagram illustrating a configuration example of a nitride semiconductor device according to an embodiment of the present disclosure.

[0022] Figure 6 This is a cross-sectional schematic diagram illustrating a configuration example of a nitride semiconductor device according to an embodiment of the present disclosure.

[0023] Figure 7 This is a cross-sectional schematic diagram illustrating a configuration example of a nitride semiconductor device according to an embodiment of the present disclosure. Detailed Implementation

[0024] The nitride semiconductor device of this disclosure will now be described through embodiments, but these embodiments do not limit the invention as claimed. Furthermore, not all combinations of features described in the embodiments are necessarily necessary for the solution of the invention.

[0025] Furthermore, in the following description, "up" and "down" do not necessarily refer to the vertical direction relative to the ground. That is, the directions of "up" and "down" are not limited to the direction of gravity. "Up" and "down" are merely convenient expressions to define the relative positional relationship of the surface, film, and substrate, etc., and do not limit the technical concept of the present invention. For example, if the paper is rotated 180 degrees, then "up" naturally becomes "down," and "down" becomes "up."

[0026] 1. First Implementation Method

[0027] The nitride semiconductor device of the first embodiment of this disclosure will be described. For example, the nitride semiconductor device of this embodiment is a laser diode.

[0028] The following explanation addresses the case where the nitride semiconductor element is a laser diode.

[0029] (1.1) Structure of a laser diode

[0030] The laser diode of this embodiment includes an Al-containing nitride semiconductor substrate and a semiconductor stack disposed on the nitride semiconductor substrate. The semiconductor stack includes: a first conductivity type cladding layer comprising a first conductivity type nitride semiconductor; a light-emitting layer disposed on the first conductivity type cladding layer and formed of a nitride semiconductor containing one or more quantum wells; and a second conductivity type cladding layer disposed on the light-emitting layer and formed of a second conductivity type Al-containing nitride semiconductor. The surface of the second conductivity type cladding layer has a vortex-shaped stepped structure with platforms and height differences, other than a straight line when viewed from above.

[0031] The following is a detailed description of each layer of the laser diode.

[0032] <Nitride Semiconductor Substrate>

[0033] The nitride semiconductor substrate (hereinafter, sometimes referred to as substrate) comprises an Al-containing nitride semiconductor. The Al-containing nitride semiconductor is, for example, AlN. That is, the substrate is preferably an AlN single-crystal substrate. However, the Al-containing nitride semiconductor is not limited to AlN; for example, it can also be AlGaN. For example, when the substrate is an AlN, AlGaN, or other nitride semiconductor single-crystal substrate, the lattice constant difference between the substrate and the nitride semiconductor layer formed on the upper side of the substrate becomes smaller. By growing the nitride semiconductor layer in a lattice-matched system, through-dislocations can be reduced.

[0034] The preferred through-dislocation density of the substrate is 5 × 10⁻⁶. 4 cm -2 The following is a further consideration. Specifically, from the viewpoint of increasing luminescence intensity and decreasing oscillation threshold current, a penetration dislocation density of 1 × 10⁻⁶ is more preferable. 3 cm -2 Above and 1×10 4 cm -2 the following.

[0035] It should be noted that as long as the substrate contains an Al-containing nitride semiconductor, it can also be formed on a heterogeneous substrate. For example, AlN can be grown on a sapphire (Al2O3) substrate.

[0036] Here, the term "containing nitride semiconductors" means that the layer primarily contains nitride semiconductors, but also includes other elements. Specifically, it includes cases where the composition of the layer is slightly altered by adding small amounts of elements other than nitride semiconductors (e.g., adding less than a few percent of Ga (where Ga is not the main element), In, As, P, or Sb). The term "containing" has the same meaning in descriptions of the composition of other layers. Furthermore, the small amounts of elements included are not limited to those mentioned above.

[0037] As an example, the substrate preferably has a layer thickness of 100 μm or more and 600 μm or less. Furthermore, regarding surface orientation, examples include: c-plane (0001), a-plane (11-20), m-plane (10-10), etc., with a c-plane (0001) substrate being more preferred. Additionally, it can be formed on a surface tilted at a certain angle (e.g., -4° to 4°, preferably -0.4° to 0.4°) measured from the normal direction of the c-plane (0001), but is not limited thereto.

[0038] <Buffer Layer>

[0039] A buffer layer may be formed on the substrate, i.e., between the substrate and the first conductivity cladding layer. The buffer layer is preferably formed on the entire surface of the substrate. By having a buffer layer, a nitride semiconductor layer with small lattice constant difference and thermal expansion coefficient difference and few defects can be formed on the buffer layer.

[0040] The buffer layer is preferably an Al-containing nitride semiconductor layer, such as AlN or AlGaN nitride semiconductors. Alternatively, the buffer layer may contain impurities such as C, Si, Fe, or Mg.

[0041] The buffer layer has a thickness of, for example, a few μm. Specifically, the thickness of the buffer layer is preferably greater than 10 nm and less than 10 μm. When the thickness of the buffer layer is greater than 10 nm, the crystallinity of nitride semiconductors such as AlN becomes higher. In addition, when the thickness of the buffer layer is less than 10 μm, cracks are less likely to occur in the buffer layer formed by crystal growth across the entire surface of the wafer.

[0042] <First conductive coating layer>

[0043] A first conductive cladding layer is formed on a substrate. Here, the phrase "on..." in the statement "a first conductive cladding layer is formed on a substrate" refers to the first conductive cladding layer being formed on one surface of the substrate. Furthermore, the presence of other layers between the substrate and the first conductive cladding layer is also included in the above description. The phrase "on..." has the same meaning in relationships between other layers. For example, the case described later, where a second conductive cladding layer is formed on the first conductive waveguide layer with an electron blocking layer in between, is also included in the statement "a second conductive cladding layer is formed on the first conductive waveguide layer."

[0044] In addition, in the description of this embodiment, "first conductivity type" and "second conductivity type" refer to semiconductors that exhibit different conductivity types, for example, one being n-type conductivity and the other being p-type conductivity.

[0045] The first conductivity cladding layer is a layer containing an Al and Ga nitride semiconductor. For example, the first conductivity cladding layer is made of Al... a Ga (1-a) N (0 < a < 1) is formed. Therefore, when a material corresponding to the bandgap energy in the deep ultraviolet region is formed as the luminescent layer, the crystallinity of the luminescent layer can be improved, thus increasing the luminous efficiency. From the viewpoint of achieving high luminous efficiency, the nitride semiconductor constituting the first conductivity cladding layer is preferably a mixture of AlN and GaN. Furthermore, from the viewpoint of growing the first conductivity cladding layer and each layer formed on the uppermost layer on the substrate in a fully strained manner, the first conductivity cladding layer is more preferably made of Al... a Ga (1-a)N (0.65 < a ≤ 0.9) is formed.

[0046] For purposes such as controlling longitudinal conductivity, the first conductive coating layer can be a gradient layer where the Al composition increases as it moves further away from the substrate. In this case, the aforementioned limitation on the Al composition can be obtained by averaging the Al composition at positions along the thickness direction within the first conductive coating layer within a range of its film thickness.

[0047] When the first conductive coating layer is an n-type conductive semiconductor layer, it may contain impurities such as Group V elements other than N (e.g., P, As, Sb), C, H, F, O, Mg, and Si, but the types of elements used as impurities are not limited to these. From the viewpoints of reducing resistance and ease of obtaining raw materials, the impurity contained in the first conductive coating layer is preferably Si, and the impurity concentration is preferably 5 × 10⁻⁶. 18 cm -3 Above and 5×10 19 cm -3 .

[0048] Furthermore, the resistivity of the first conductive coating layer is preferably 1×10⁻⁶. -3 Ωcm or more and 5×10 -3 Below Ωcm. Therefore, carrier injection can be performed efficiently.

[0049] From the viewpoints of lattice relaxation within the first conductive coating layer and film resistance, the first conductive coating layer preferably has a thickness of 250 nm or more and 800 nm or less, and more preferably has a thickness of 300 nm or more and 450 nm or less.

[0050] <Emitting Layer>

[0051] The light-emitting layer is a layer containing Al and Ga nitride semiconductors. From the viewpoint of achieving high luminous efficiency, the nitride semiconductor contained in the light-emitting layer is preferably, for example, a mixed crystal of AlN and GaN, such as Al... b Ga (1-b) N (0 < b < 1) is formed. The luminescent layer may contain impurities such as P, As, Sb and other Group V elements other than N, C, H, F, O, Mg, Si and other elements, but the types of elements used as impurities are not limited to these.

[0052] Furthermore, the light-emitting layer can employ a multi-quantum-well structure or a single-quantum-well structure. Although the number of quantum well structures varies depending on the longitudinal conductivity of the first and second conductive coating layers, it is preferably any one of 1 to 5.

[0053] In the laser diode of this embodiment, it is preferable that the potential fluctuation α of the nitride semiconductor layer is 130 meV or more and 350 meV or less. The nitride semiconductor layer represented by such α can be not only a light-emitting layer, but also a first conductive waveguide layer or a second conductive waveguide layer, described later. When the α of the light-emitting layer, the first conductive waveguide layer, or the second conductive waveguide layer is 130 meV or more and 350 meV or less, the recombination of locally present charge carriers can occur effectively, thereby improving the luminous efficiency.

[0054] Here, "potential fluctuation of the nitride semiconductor layer" is an indicator used to define the distribution state of Ga in the planar direction of the nitride semiconductor layer, and "α, which indirectly represents the potential fluctuation," is an indicator of the deviation of the uniformity of the alloy in the planar direction of the nitride semiconductor layer. In the case of α being (approximately) 30 meV, it indicates that Ga is uniformly distributed in the planar direction of the nitride semiconductor layer, that is, Al and Ga are uniformly arranged.

[0055] Such potential fluctuations manifest as the full width at half maximum (FWHM) of the emission spectrum of the nitride semiconductor layer. That is, the closer the nitride semiconductor layer is to a perfectly homogeneous crystal, the narrower the FWHM of the emission spectrum. On the other hand, the possible values ​​of the FWHM of the emission spectrum vary depending on the Al composition of the nitride semiconductor. Therefore, the potential fluctuations of the nitride semiconductor layer are evaluated using α, which represents the deviation of the FWHM from the uniform state of each Al composition. The Al composition x of the nitride semiconductor layer and the FWHM of the emission spectrum at the emission wavelength can be expressed by the formula FWHM(meV) = αx + 10meV. Here, a larger α indicates a greater degree of deviation from the uniform state, i.e., the presence of segregation or localization of elements such as Ga.

[0056] Furthermore, at the interface between the trap layer and the barrier layer in the light-emitting layer, the thickness of the region where the Al concentration distribution gradually changes is preferably 0.3 nm or more and 0.6 nm or less.

[0057] This improves carrier confinement and increases luminescence intensity.

[0058] Waveguide layer

[0059] From the viewpoint of light confinement in a laser diode, the laser diode of this embodiment may include a waveguide layer formed above and below the light-emitting layer, with the light-emitting layer sandwiched in between, and thus confining the light emitted from the light-emitting layer within the light-emitting layer. Preferably, the waveguide layer consists of two layers: a first conductive waveguide layer disposed between a first conductive cladding layer and the light-emitting layer, and a second conductive waveguide layer disposed between a second conductive cladding layer and the light-emitting layer.

[0060] That is, the laser diode of this embodiment may include, for example, a first conductive waveguide layer disposed between a first conductive cladding layer and a light-emitting layer to confine light in the light-emitting layer; and a second conductive waveguide layer disposed between a second conductive cladding layer and a light-emitting layer to confine light in the light-emitting layer.

[0061] From the viewpoint of light confinement, the waveguide layer is preferably a nitride semiconductor containing Al or Ga, having a band gap with higher energy than the light-emitting layer. The waveguide layer preferably has an Al composition and film thickness that increases the overlap between the electric field intensity distribution of the standing wave light within the device and the light-emitting layer. From the viewpoint of confining charge carriers within the light-emitting layer, Al is used in the light-emitting layer. b Ga (1-b) N (0 < b < 1), waveguide layer uses Al c Ga (1-c) When N (0 < c < 1), b < c, and more preferably c ≥ b + 0.05. For example, in the case of an emitting layer with an emission wavelength of 265 nm, b is preferably 0.52 and c is preferably 0.57 or more.

[0062] Furthermore, from the viewpoint of light confinement and layer resistance, the total thickness of the waveguide layer (the sum of the thicknesses of the first conductive waveguide layer and the second conductive waveguide layer) is preferably 70 nm or more and 150 nm or less.

[0063] The waveguide layer can contain impurities such as P, As, Sb (excluding N), Group V elements, C, H, F, O, Mg, and Si, but the types of elements used as impurities are not limited to these. From the perspective of reducing resistance and the ease of obtaining raw materials, the impurity contained in the first conductive waveguide layer is preferably Si, and the impurity concentration is preferably 5 × 10⁻⁶. 18 cm -3 Above and 5×10 19 cm -3 .

[0064] The Al composition of the first conductive waveguide layer and the second conductive waveguide layer is preferably uniform in the thickness direction, but is not limited thereto. To avoid light absorption by the metal (e.g., the second electrode) present above the second conductive cladding layer (described later), the Al composition of the second conductive waveguide layer may be higher than that of the first conductive waveguide layer. For the same purpose, the thickness of the second conductive waveguide layer may be greater than that of the first waveguide.

[0065] <Second conductive coating layer>

[0066] A second conductivity cladding layer is formed on the light-emitting layer, and it is a nitride semiconductor layer containing Al and Ga with a second conductivity type. The second conductivity cladding layer is, for example, made of Al... dGa (1-d) N (0.1≤d≤1) is formed. Specifically, a second conductivity cladding layer is formed on the second conductivity waveguide layer. As a result, the second conductivity cladding layer can easily match the lattice of the light-emitting layer or the waveguide layer, and can suppress the penetration dislocation density.

[0067] The second conductivity cladding layer possesses sufficient conductivity to inject charge carriers (electrons or holes) into the light-emitting layer. The conductivity type is not particularly limited as long as the overlap between the electric field intensity distribution of the standing wave optical mode within the device and the light-emitting layer is increased (i.e., the light confinement is increased). For example, the second conductivity cladding layer can be p-type AlGaN doped with Mg. Furthermore, the second conductivity cladding layer can contain impurities such as Group V elements other than N (P, As, Sb), C, H, F, O, Mg, and Si, but the types of impurities are not limited to these.

[0068] From the perspective of more efficiently injecting charge carriers into the light-emitting layer, the second conductive coating layer is composed of a gradually decreasing Al composition (d) as it moves away from the substrate. d Ga (1-d) The composition of the N (0.1≤d≤1) layer is a gradient layer, but in a portion of the second conductive coating layer, the Al composition d increases as it moves away from the substrate.

[0069] The second conductive cladding layer preferably has a compositional gradient where the Al composition d decreases from 1 to 0.7 as it moves away from the nitride semiconductor substrate. The distribution (gradual change) of the Al composition d in the second conductive cladding layer can decrease continuously or intermittently. Here, "intermittent decrease" means that a portion of the film in the second conductive cladding layer contains a portion with the same Al composition d (constant in the film thickness direction). That is, the second conductive cladding layer may also include portions where the Al composition d does not decrease in the direction away from the substrate (portions where the Al composition d is constant or increases).

[0070] From the viewpoint of lattice matching, the thickness of the second conductive coating layer is preferably 500 nm or less. Furthermore, from the viewpoint of light confinement, it is more preferably 250 nm or more and 500 nm or less.

[0071] Figure 1 The diagram shows the Al composition (in bold lines) and impurity composition (in solid lines) of each layer of the laser diode. It should be noted that... Figure 1 The diagram shows a structure without a buffer layer as an example.

[0072] like Figure 1As shown, the second conductive cladding layer is composed in a gradient such that the Al composition d decreases as it moves away from the substrate. Impurities such as carbon or oxygen are doped into a portion of the second conductive cladding layer. For example, impurities are also doped into the interface gradient portion where the Al composition increases on the second conductive waveguide layer, where the concentration distribution increases discontinuously at the starting point of this composition gradient layer (the interface on the second conductive waveguide layer side).

[0073] Previously, second conductive cladding layers were mostly formed from almost undoped nitride semiconductors for purposes such as suppressing impurity diffusion and thus improving implantation efficiency. However, by including a large number of impurities in a portion of the second conductive cladding layer, the second conductive cladding layer can simultaneously suppress degradation and improve implantation efficiency.

[0074] Furthermore, the second conductive coating layer preferably has a region where the concentration distribution of carbon or oxygen contained in the second conductive coating layer varies discontinuously with distance from the substrate at least once. That is, it is preferable that the impurity concentration distribution has a region bulging towards a higher concentration. By having such a discontinuous region, the second conductive coating layer has a portion that achieves the effect of suppressing the degradation of the second conductive coating layer and the remaining portion that achieves the effect of improving the injection efficiency of charge carriers (electrons or holes) into the light-emitting layer. In this case, the concentration distribution of carbon or oxygen in the second conductive coating layer gradually changes with a steep slope, improving the effect of improving the injection efficiency of charge carriers into the light-emitting layer, and the second conductive coating layer can simultaneously achieve the effects of suppressing the degradation of the second conductive coating layer and improving the injection efficiency of charge carriers into the light-emitting layer. Generally, when the impurity concentration distribution has a region that bulges towards higher concentration, it is disadvantageous in terms of carrier injection efficiency into the luminescent layer. However, depending on the thickness of the second coating layer, setting a region where the carbon or oxygen concentration distribution gradually changes with a steep slope is advantageous in terms of overall carrier injection efficiency into the luminescent layer.

[0075] Here, "a region where the concentration distribution decreases discontinuously with distance from the substrate (nitride semiconductor substrate)" refers to a region where the impurity concentration (the impurity concentration measured at a measurement point in that region) differs from the impurity concentration in the surrounding areas (the impurity concentration measured at measurement points in adjacent regions) by more than a factor of two. For example, such as Figure 1 As shown, region P exhibits a sharp change in the concentration distribution of impurities.

[0076] As described above, the second conductive coating layer has a region P in which the concentration distribution of impurities decreases discontinuously. This region P, where the concentration distribution decreases discontinuously, preferably exists in a region of the second conductive coating layer measuring 1 nm or more and 110 nm or less from the substrate side, and more preferably in a region of the second conductive coating layer measuring 5 nm or more and 110 nm or less from the substrate side. Therefore, the degradation of the second conductive coating layer can be suppressed without hindering the improvement of carrier injection efficiency into the light-emitting layer.

[0077] Furthermore, the region closer to the substrate side in the second conductive coating layer, where the concentration distribution of impurities decreases discontinuously compared to the region P, is preferably made of Al. e Ga (1-e) N (0.8≤e≤1.0) is formed. Thus, the degradation of the second conductivity coating layer can be suppressed without hindering the improvement of carrier injection efficiency into the light-emitting layer.

[0078] The carbon concentration in the region closer to the substrate side of region P, where the concentration distribution of impurities decreases discontinuously compared to the second conductive coating layer, is preferably 1 × 10⁻⁶. 17 cm -3 Above and 1×10 18 cm -3 Similarly, in the second conductive coating layer, the oxygen concentration in the region closer to the substrate side than the region P where the impurity concentration distribution decreases discontinuously is preferably 1 × 10⁻⁶. 17 cm -3 Above and 1×10 18 cm -3 Therefore, layers that effectively suppress the degradation of the second conductivity type coating layer and improve the carrier injection efficiency into the light-emitting layer are respectively formed. Thus, it is possible to more effectively combine the effects of suppressing the degradation of the second conductivity type coating layer in the laser diode and improving the carrier injection efficiency into the light-emitting layer.

[0079] As mentioned above, Figure 1 The second conductive coating layer of the embodiment shown contains Al d Ga (1-d) N (0.1≤d≤1) and has a compositional gradient where the Al composition d decreases with increasing distance from the nitride semiconductor substrate. Furthermore, at least a portion of the second conductivity cladding layer is a compositional discontinuity region Q where the Al composition is discontinuous in the direction away from the substrate, and in this discontinuity region Q, the Al composition d increases with increasing distance from the substrate. By having the compositional discontinuity region Q in this way, the laser diode can simultaneously suppress the degradation of the second conductivity cladding layer and improve the carrier injection efficiency into the light-emitting layer.

[0080] The discontinuous region Q preferably exists in a region of the second conductive coating layer that is 1 nm or more and 110 nm or less from the nitride semiconductor substrate side, more preferably in a region of the second conductive coating layer that is 5 nm or more and 110 nm or less from the nitride semiconductor substrate side. That is, the starting point of the discontinuous region Q preferably coincides with the starting point of region P. By having the discontinuous region Q on the nitride semiconductor substrate side of the second conductive coating layer, the degradation of the second conductive coating layer can be suppressed without hindering the improvement of the carrier injection efficiency into the light-emitting layer.

[0081] Furthermore, the discontinuous region Q preferably has a compositional gradient where the Al composition d increases by 0.002 or more but less than 0.05 as it moves away from the substrate. By forming the discontinuous region Q with such a compositional gradient, layers that achieve the effect of suppressing the degradation of the second conductivity type cladding layer and layers that achieve the effect of improving the injection efficiency of charge carriers into the light-emitting layer are formed. Therefore, it is possible to more effectively combine the effects of suppressing the degradation of the second conductivity type cladding layer in the laser diode and improving the injection efficiency of charge carriers into the light-emitting layer.

[0082] Furthermore, the interface on the substrate side of the second conductive cladding layer (i.e., the interface with the second conductive waveguide layer) preferably contains 1×10 17 cm -3 Above and 5×10 19 cm -3 The hydrogen content is as follows. Preferably, the hydrogen content in at least a portion of the second conductive coating layer is higher than in other regions of the second conductive coating layer. It should be noted that while the second conductive coating layer contains trace amounts of hydrogen overall, the second conductive coating layer of the laser diode in this embodiment includes regions (these regions) that locally contain high concentrations of hydrogen. Therefore, the laser diode can compensate for point defects and simultaneously suppress the degradation of the second conductive coating layer and improve the carrier injection efficiency into the light-emitting layer.

[0083] The region containing hydrogen at a higher concentration than other regions of the second conductive coating layer is preferably a region of the second conductive coating layer measuring 1 nm or more and 110 nm or less from the substrate side, more preferably a region of the second conductive coating layer measuring 5 nm or more and 110 nm or less from the substrate side. This allows for the compensation of point defects and suppresses the degradation of the second conductive coating layer without hindering the improvement of carrier injection efficiency into the light-emitting layer.

[0084] Furthermore, the full width at half maximum (FWHM) of the hydrogen concentration distribution in the region containing hydrogen at a higher concentration than other regions of the second conductive coating layer is preferably 5 nm or more and 10 nm or less. This effectively compensates for point defects and improves the carrier injection efficiency into the light-emitting layer.

[0085] Additionally, the interface on the substrate side of the second conductive coating layer may contain 1×10 17 cm -3 Above and 5×10 19 cm -3 The following refers to silicon. Silicon may be contained in at least a portion of the second conductive coating at a higher concentration than in other regions of the second conductive coating. The region containing silicon at a higher concentration than in other regions of the second conductive coating is preferably a region of the second conductive coating measuring 1 nm or more and 110 nm or less from the substrate side, more preferably a region of the second conductive coating measuring 5 nm or more and 110 nm or less from the substrate side.

[0086] like Figure 2A As shown, the surface of the aforementioned second conductive coating layer has a vortex-like step-terrace structure with platforms and elevation differences, in addition to a straight line shape when viewed from above. One example of the vortex-like step-terrace structure is a shape based on a hexagon with a portion of its outline gradually shortening. Another example of the vortex-like step-terrace structure is a shape based on a circle with its radius gradually shortening, or a shape based on a mixture of hexagons and straight lines with the length of its sides gradually shortening. Here, for comparison, in Figure 3 The diagram shows a linear, stepped structure with platforms and elevation differences when viewed from above. This allows for a better balance between suppressing the degradation of the second conductivity cladding layer in the laser diode and improving the efficiency of carrier injection into the emitting layer.

[0087] This second conductive coating is formed by growing it at a lower temperature than before (described in detail later), thereby transforming the linear step structure into a vortex-like step structure. Here, Figure 2A This is an atomic force microscopy (AFM) image showing a swirling, stepped structure. Figure 2B This is a scanning electron microscope (SEM) image showing a circular stepped structure. Compared to circular or linear stepped structures formed on the surface of the second conductive coating, the formation of a vortex-shaped stepped structure results in a higher luminescence efficiency of the second conductive coating. This is believed to be due to Ga segregation during the film growth process of the vortex-shaped stepped structure, thereby improving the current injection efficiency.

[0088] The height of the vortex-shaped stepped structure is preferably above 0.2 nm and below 0.4 nm.

[0089] Furthermore, the preferred distribution density of the vortex-shaped step structure is 1×10⁻⁶.7 cm -2 Above and 5×10 8 cm -2 the following.

[0090] This results in a greater ability to suppress the degradation of the second conductive coating layer and improve current injection efficiency.

[0091] It should be noted that when a second conductive cladding layer is formed by conventional methods after forming a nitride semiconductor layer with a vortex-like stepped structure, a vortex-like stepped structure also appears on the surface of the second conductive cladding layer. Therefore, the vortex-like stepped structure on the surface of the second conductive cladding layer can be confirmed by observing its surface shape. However, when a second conductive contact layer (described later) is formed on the second conductive cladding layer, the vortex-like stepped structure no longer appears on the surface of the second conductive contact layer. However, for example, the vortex-like stepped structure on the surface of the second conductive cladding layer can be confirmed by removing only the second conductive contact layer using sulfur hexafluoride (SF6) gas, exposing the second conductive contact layer, and observing it using SEM or similar methods.

[0092] <Interface Gradient Section>

[0093] The laser diode in this embodiment may have an interface gradient section on the light-emitting layer (second conductive waveguide), the interface gradient section comprising Al g Ga (1-g) N (0.1≤g≤1), and the Al composition g increases as one moves away from the nitride semiconductor substrate. By providing an interface gradient section like in this embodiment, the electric field is relaxed, thereby improving the degradation suppression effect.

[0094] Furthermore, the film thickness of the interface gradient section is preferably 2 nm or more and 5 nm or less, and more preferably 2 nm or more and 3 nm or less. In this case, the degradation suppression effect is further improved.

[0095] <Second conductive contact layer>

[0096] The semiconductor stack of the laser diode in this embodiment may further include a second conductive contact layer disposed on the second conductive cladding layer. The nitride semiconductor constituting the second conductive contact layer is preferably formed of GaN, AlN, or InN and mixed crystals containing them, and more preferably a nitride semiconductor containing GaN.

[0097] When the second conductive contact layer is a p-type contact layer, impurities such as P, As, Sb (excluding N), Group V elements, C, H, F, O, Mg, Si, and Be can be mixed in. Considering the versatility of the raw material gas, Mg is preferably the impurity contained in the second conductive contact layer. From the viewpoint of reducing contact resistance, the concentration of Mg is preferably 8 × 10⁻⁶. 19 cm -3 Above and 5×10 21 cm -3 The following is more preferably 5×10 20 cm -3 Above and 5×10 21 cm -3 the following.

[0098] Furthermore, the thickness of the second conductive contact layer is preferably 1 nm or more and 20 nm or less. The thinner the second conductive contact layer, the higher the carrier injection efficiency of the light-emitting layer; conversely, the thicker the second conductive contact layer, the lower the carrier injection efficiency.

[0099] <Electron blocking layer>

[0100] In this embodiment, the semiconductor stack of the laser diode may have an electron blocking layer with a band gap larger than that of the light-emitting layer above the light-emitting layer. The electron blocking layer may be disposed, for example, on the light-emitting layer, or inside the second conductive waveguide layer, between the second conductive waveguide layer and the light-emitting layer, or between the second conductive waveguide layer and the second conductive cladding layer.

[0101] In order to facilitate quantum penetration of charge carriers (holes) through the electron blocking layer, the thickness of the electron blocking layer is preferably less than 30 nm, and more preferably less than 20 nm.

[0102] <Electrode>

[0103] A laser diode can emit light or oscillate by injecting current using a second electrode disposed on a second conductive cladding layer and a first electrode disposed on a first conductive cladding layer. In this case, the first electrode is formed in electrical contact with the first conductive cladding layer, and the second electrode is formed in electrical contact with the second conductive cladding layer.

[0104] Regarding the first electrode, for example, the electrode can be disposed on the back side of the substrate. Alternatively, the first electrode can be disposed on a first conductive cladding layer exposed by, for example, removing the upper layer of the first conductive cladding layer of the semiconductor stack through chemical etching or dry etching. That is, the first electrode is disposed in a region of the first conductive cladding layer where no mesa structure is formed.

[0105] When the first conductive coating layer is an n-type coating layer, the first electrode is formed from metals such as Al, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zr, their mixed crystals, or conductive oxides such as ITO or Ga2O3.

[0106] When the first conductive coating layer is a p-type coating layer, the first electrode is formed from metals such as Ni, Au, Pt, Ag, Rh, Pd, Pt, Cu, Al, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Co, Ir, Zr, their mixed crystals, or conductive oxides such as ITO or Ga2O3.

[0107] When the second conductive coating layer is an n-type coating layer, the second electrode is formed from metals such as Al, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zr, their mixed crystals, or conductive oxides such as ITO or Ga2O3.

[0108] When the second conductive coating layer is a p-type coating layer, the second electrode is formed from metals such as Ni, Au, Pt, Ag, Rh, Pd, Pt, Cu, Al, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Co, Ir, Zr, their mixed crystals, or conductive oxides such as ITO or Ga2O3.

[0109] There are no restrictions on the configuration area and shape of the first and second electrodes, as long as they are electrically contacted with the first conductive coating layer and the second conductive coating layer (or the second conductive contact layer if a second conductive contact layer is present).

[0110] (1.2) Manufacturing methods of nitride semiconductor laminates and nitride semiconductor devices

[0111] The laser diode, which is a nitride semiconductor element in this embodiment, can be manufactured by forming a nitride semiconductor stack, which is manufactured through a process of forming each layer of nitride semiconductor layer on a substrate, into a single wafer. Hereinafter, a method for manufacturing a nitride semiconductor stack and a method for manufacturing a laser diode, which is an example of a method for manufacturing a nitride semiconductor element, will be described.

[0112] (1.2.1) Method for manufacturing nitride semiconductor laminate

[0113] (Substrate formation)

[0114] The substrate is formed using conventional substrate growth methods such as sublimation, hydride vapor phase growth (HVPE), and liquid phase growth.

[0115] (Formation of semiconductor stack)

[0116] The individual layers of the semiconductor stack formed on the substrate can be formed, for example, by molecular beam epitaxy (MBE), hydride vapor phase growth (HVPE), or metal-organic chemical vapor phase growth (MOCVD).

[0117] Here, the nitride semiconductor layers formed on the substrate can be formed, for example, using an Al material containing trimethylaluminum (TMAl), a Ga material containing trimethylgallium (TMGa) or triethylgallium (TEGa), or an N material containing ammonia (NH3).

[0118] A semiconductor stack is formed on a substrate. At this time, an organometallic gas is introduced into the semiconductor stack formation space. First, a first conductivity type cladding layer comprising a nitride semiconductor of a first conductivity type is formed on the substrate.

[0119] Next, a first conductive waveguide layer based on a nitride semiconductor such as AlGaN is formed on the first conductive cladding layer, and then a light-emitting layer is formed from a nitride semiconductor (AlGaN, etc.) containing one or more quantum wells. Then, a second conductive waveguide layer based on a nitride semiconductor such as AlGaN is formed on the light-emitting layer.

[0120] At this time, the formation of the first conductive waveguide layer, the light-emitting layer, and the second conductive waveguide layer is preferably performed under the condition that -2Tw+2050<Vw<-2Tw+2350 (850℃<Tw<970℃) is satisfied when the wafer temperature is set to Tw and the reactor pressure is set to Vw.

[0121] This allows the formation of a light-emitting layer with Ga unevenly distributed along the planar direction of the nitride semiconductor layer. Similarly, a first conductivity waveguide and a second conductivity waveguide with Ga unevenly distributed along the planar direction of the nitride semiconductor layer can also be formed. This results in localized carrier presence, increasing the recombination ratio and improving luminous efficiency.

[0122] Next, a second conductive cladding layer is formed on the second conductive waveguide layer.

[0123] First, before forming part of the second conductive coating layer, the inflow of organometallic gas is temporarily stopped to interrupt the growth of the nitride semiconductor layer, and the film formation conditions are changed.

[0124] Next, preferably, the conditions are changed to a wafer temperature of 900°C or higher and 1000°C or lower, and a reactor pressure of 15 mbar or higher and 350 mbar or lower, and the flow of organometallic gas is started again, thereby forming part of the second conductivity type coating layer by the second conductivity type nitride semiconductor.

[0125] After a portion of the second conductive coating layer has been formed, but before the remainder of the second conductive coating layer has been formed, the inflow of the organometallic gas is temporarily stopped again to interrupt the growth of the nitride semiconductor layer, and the film formation conditions are changed.

[0126] Next, the conditions were changed to a wafer temperature of 1030°C or higher and 1100°C or lower, and a reactor pressure of 15 mbar or higher and 350 mbar or lower, and the flow of organometallic gas was started again, thereby forming the remaining part of the second conductive coating layer.

[0127] By forming the first conductive cladding layer, the first conductive waveguide layer, the light-emitting layer, and the second conductive waveguide layer in the manner described above, the recombination ratio of charge carriers can be increased and the point defects in each layer can be reduced, thereby improving degradation suppression and luminescence efficiency.

[0128] Furthermore, by setting the wafer temperature at which a portion of the second conductive cladding layer is formed to be lower than the wafer temperature at which the remaining portion of the second conductive cladding layer is formed, at least one region can be formed in which the carbon or oxygen concentration distribution in both the portion of the second conductive cladding layer and the remaining portion of the second conductive cladding layer decreases discontinuously with distance from the substrate. That is, the portion of the second conductive cladding layer can be formed with a higher carbon or oxygen content compared to the remaining portion of the second conductive cladding layer. Therefore, the second conductive cladding layer can simultaneously suppress degradation and improve implantation efficiency.

[0129] Furthermore, by setting the reactor pressure when forming a portion of the second conductive coating layer to a lower pressure than the reactor pressure when forming the remainder of the second conductive coating layer, the portion of the second conductive coating layer can be formed in a manner that contains more carbon or oxygen as impurities compared to the remainder of the second conductive coating layer.

[0130] Furthermore, by temporarily halting the inflow of the organometallic gas before forming a portion of the second conductive cladding layer, hydrogen and silicon are locally present at the substrate-side interface of the second conductive cladding layer. This is because, for example, when using hydrogen (H2) as the carrier gas, hydrogen (H) tends to be locally present in the uppermost layer of the nitride semiconductor layer that interrupts growth (e.g., the interface between the second conductive waveguide layer and the second conductive cladding layer, and a portion of the second conductive cladding layer). Therefore, for laser diodes, the effect of suppressing the degradation of the second conductive cladding layer and improving the efficiency of carrier injection into the light-emitting layer can be further enhanced.

[0131] Previously, when the growth of a nitride semiconductor layer was interrupted, some elements (e.g., Ga in the case of AlGaN) would detach, so growth interruption was avoided as much as possible. However, by interrupting the growth and actively introducing hydrogen, so that hydrogen is locally present at the interface between the second conductive waveguide layer and the second conductive cladding layer, and in a portion of the second conductive cladding layer, it is possible to achieve V III The -H3 method compensates for point defects in the interface, thereby improving the degradation suppression effect.

[0132] Furthermore, conventionally, when the second conductivity cladding layer is a p-type semiconductor layer, it is preferable not to include silicon that becomes an n-type impurity. However, by interrupting the growth process and actively introducing silicon, so that silicon from the raw material or substrate is locally present at the interface between the second conductivity waveguide layer and the second conductivity cladding layer, as well as in a portion of the second conductivity cladding layer, point defects at the interface can be compensated, thereby improving the degradation suppression effect.

[0133] It should be noted that, as described above, in this embodiment, by setting the wafer temperature when forming a portion of the second conductive cladding layer to a lower temperature than the wafer temperature when forming the remaining portion of the second conductive cladding layer, at least one region is formed in which the carbon or oxygen concentration distribution in the portion of the second conductive cladding layer and the remaining portion of the second conductive cladding layer decreases discontinuously with distance from the substrate. However, this manufacturing method is not limited to this. For example, the flow rate of the organometallic gas may be intentionally varied during the formation of the second conductive cladding layer to form a region in which the carbon or oxygen concentration distribution decreases discontinuously with distance from the substrate.

[0134] In addition, depending on the needs, an intermediate layer can be formed between the second conductive cladding layer and the second conductive waveguide layer using nitride semiconductors such as AlGaN, or a second conductive contact layer can be formed on the second conductive cladding layer using nitride semiconductors such as GaN, or an electron blocking layer can be formed above the light-emitting layer.

[0135] (1.2.2) Manufacturing method of nitride semiconductor device (laser diode)

[0136] (The formation of the countertop structure)

[0137] Laser diodes are manufactured through a process (mesa structure formation process) in which unwanted portions of each layer of a semiconductor stack are removed by etching on a substrate. The removal of unwanted portions of each layer of the semiconductor stack can be performed, for example, by inductively coupled plasma (ICP) etching.

[0138] In the process of forming the table structure, unwanted portions of each layer of the conductor stack are removed by etching, thereby exposing a portion of the first conductive cladding layer.

[0139] (Electrode formation)

[0140] Furthermore, laser diodes can be manufactured through an electrode formation process. Electrodes such as the first and second electrodes are formed, for example, by various methods of metal deposition via electron beam evaporation (EB), such as resistance heating evaporation, electron gun evaporation, or sputtering, but are not limited to these methods. Each electrode can be formed as a single layer or stacked in multiple layers.

[0141] In addition, each electrode can be heat-treated in an oxygen, nitrogen, or air atmosphere after the metal layer is formed.

[0142] (Mono-chip)

[0143] Finally, the substrate with each layer formed by the above process is cut into individual pieces to manufacture nitride semiconductor devices (laser diodes).

[0144] Specifically, a first electrode is formed on the surface of the first conductive cladding layer. A second electrode is formed on the uppermost layer (e.g., the second conductive cladding layer) of a mesa structure formed from a portion of the semiconductor stack. The formed electrode is alloyed by heating using a rapid thermal annealing (RTA) device (heat treatment with an infrared lamp) or by laser annealing (heat treatment with a laser pulse), thus achieving contact with the semiconductor stack. At this point, the alloying method is not particularly limited as long as sufficient contact with the semiconductor stack can be achieved.

[0145] The laser diode manufactured according to the manufacturing method of the nitride semiconductor element of this embodiment can improve carrier injection efficiency and increase luminous intensity.

[0146] (1.3) Methods for determining the physical properties of laser diodes, etc.

[0147] The physical properties of the aforementioned laser diodes can be determined as follows.

[0148] (Methods for determining layer thickness)

[0149] The thickness of each layer constituting a laser diode can be determined by the following method: a predetermined cross-section perpendicular to the substrate is cut out, and this cross-section is observed using a transmission electron microscope (TEM). The length measurement function of the TEM is then used for measurement. As a measurement method, firstly, the cross-section perpendicular to the main surface of the laser diode substrate is observed using a TEM. Specifically, for example, the observation width is defined as a range of 2 μm or more in the direction parallel to the main surface of the substrate within the TEM image showing the cross-section perpendicular to the main surface of the laser diode substrate. Within this observation width, light and dark contrasts are observed at the interface between two different layers. Therefore, the thickness up to this interface is observed within a continuous observation region of 200 nm width. The average thickness of each layer within the 200 nm observation region is calculated based on five points randomly selected from the aforementioned observation width of 2 μm or more, thereby obtaining the thickness of each layer.

[0150] (Determination of impurity concentration and doping concentration)

[0151] The concentrations of dopants and impurities contained in each layer of a laser diode can be determined by secondary ion mass spectrometry (SIMS).

[0152] When determining the concentration of dopants and impurities in each layer using SIMS after device fabrication, the measurement can be performed even after the electrodes have been removed by chemical etching or physical polishing. Alternatively, the concentration of dopants and impurities in each layer can be measured by sputtering from the substrate side where no electrodes have been formed.

[0153] Specifically, SIMS measurements were performed under the conditions provided by Evans Analytical Group (EAG). A cesium (Cs) ion beam with an energy of 14.5 keV was used for sample sputtering during the measurements.

[0154] (Methods for determining the atomic concentration of each layer)

[0155] One method for determining the atomic concentration in each layer constituting a laser diode is reciprocal space mapping (RSM) based on X-ray diffraction (XRD). Specifically, the lattice relaxation rate and Al composition relative to the substrate are obtained by analyzing the reciprocal space mapping data near the diffraction peaks obtained using the asymmetric plane as the diffraction plane. Examples of diffraction planes include the (10-15) plane and the (20-24) plane.

[0156] In addition, for layers or regions where sufficient reflection intensity cannot be obtained using XRD, such as luminescent layers, gradient layers, and small hillocks formed in each layer, X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDX), and electron energy-loss spectroscopy (EELS) can be used for determination.

[0157] In EELS, the composition of a sample is analyzed by measuring the energy lost as electron beams pass through it. Specifically, for example, for thin-film samples used in TEM observation, the energy loss spectrum of the transmitted electron beam intensity is measured and analyzed. Then, by utilizing the variation in peak positions around the energy loss of 20 eV according to the composition of each layer, the composition can be determined from the peak positions.

[0158] Similar to the layer thickness calculation method based on TEM observation mentioned above, the average value of Al composition within a 200 nm observation width range is calculated from 5 randomly selected locations in the observation area above 2 μm, thereby obtaining the Al composition of each layer.

[0159] In EDX, for the thin-film specimens used in the aforementioned TEM observations, characteristic X-rays generated using electron beams are measured and analyzed. Similar to the layer thickness calculation method based on TEM observations, the average Al composition of each layer is obtained by calculating the average value of the Al composition within a 200 nm observation width range from five randomly selected locations in the observation area of ​​2 μm or more.

[0160] In XPS, depth direction evaluation can be performed by conducting XPS measurements simultaneously with sputtering etching using an ion beam. Ar+ is typically used as the ion beam, but other ion types, such as Ar cluster ions, can be used, as long as they can be irradiated by the etching ion gun mounted in the XPS device. The depth direction distribution of Al composition in each layer is obtained by measuring and analyzing the XPS peak intensities of Al, Ga, and N. Alternatively, instead of sputtering etching, the laser diode can be tilted and ground to enlarge the cross-section perpendicular to the main surface of the substrate, and then the exposed cross-section can be measured using XPS.

[0161] The composition of each layer can be determined not only using XPS but also using Auger electron spectroscopy (AES). In this case, the composition can be determined by performing Auger electron spectroscopy-based measurements on the cross-section exposed by sputter etching or tilted grinding. Alternatively, the composition of each layer can also be determined by SEM-EDX measurements on the cross-section exposed by tilted grinding.

[0162] (Methods for measuring potential fluctuations)

[0163] The potential fluctuation α, indirectly representing the potential fluctuation, is calculated using the formula FWHM(meV) = αx + 10meV, based on the Al composition x of the nitride semiconductor layer and the full width at half maximum (FWHM) at the emission wavelength. Specifically, FWHM is obtained from the emission spectrum obtained by photoluminescence measurement of the nitride semiconductor layer. α is obtained by using the Al composition x of the nitride semiconductor layer. In this case, the photoluminescence measurement uses a light source with a wavelength shorter than the bandgap of the nitride semiconductor layer to be excited. For example, a third harmonic laser of YAG at 213 nm is used. More accurate values ​​can be obtained by performing the measurement while cooling the sample to below 10 K. Furthermore, in the case of a layer with a bandgap smaller than the desired nitride semiconductor layer, the specific layer can be measured by removing that layer using etching or the like. Specifically, in the case of a light-emitting layer on a first conductive waveguide layer, since the quantized light-emitting layer is excited by the excitation light, an accurate value can be obtained by measuring the first conductive waveguide layer after removing the light-emitting layer by etching.

[0164] (Methods for measuring surface shape)

[0165] Methods for determining the surface shape of the second conductive coating include: scanning electron microscopy (SEM) and atomic force microscopy (AFM).

[0166] Specifically, the surface of the second conductive coating layer was observed using a scanning electron microscope SU9000 manufactured by Hitachi Advanced Technology Co., Ltd., under an accelerating voltage of 30 kV. At this time, by setting the magnification to 10K to 50K, the surface shape of the second conductive coating layer could be clearly observed. The number of vortex-like step structures contained within the observation range under these conditions was counted, and the value obtained by dividing by the area was taken as the density of the vortex-like step structures.

[0167] The height difference of the vortex-like stepped structure on the surface of the second conductive coating can be determined by AFM (Aspect-Factor Microscopy). Specifically, it is observed using a scanning probe microscope manufactured by Hitachi Advanced Technology Co., Ltd. When observing with the scanning probe microscope, a 2μm square area is observed using AFM mode. The step height can be determined from the obtained AFM image.

[0168] (Application areas of nitride semiconductor devices)

[0169] The laser diode disclosed herein can be applied, for example, to devices in the medical / life sciences, environmental, industrial, household / appliance, agricultural, and other fields. Laser diodes can be used in devices for the synthesis / decomposition of pharmaceuticals or chemicals, sterilization devices for liquids / gases / solids (containers, food, medical devices, etc.), cleaning devices for semiconductors, surface modification devices for films / glass / metals, exposure devices for semiconductor / FPD (flat panel display) / PCB (printed wiring board) / other electronic product manufacturing, printing / coating devices, bonding / sealing devices, transfer / forming devices for films / patterns / models, and measuring / inspecting devices for banknotes / damage / blood / chemical substances, etc.

[0170] Examples of liquid sterilization devices include: automatic ice makers / ice trays and ice storage containers in refrigerators / water tanks for ice makers, freezers, ice makers, humidifiers, dehumidifiers, cold water tanks / hot water tanks / flow pipes in water dispensers, stationary water purifiers, portable water purifiers, water supply devices, water heaters, wastewater treatment devices, garbage disposers, water traps in toilets, washing machines, sterilization modules for dialysis water, sterilization devices for peritoneal dialysis connectors, and disaster relief water storage systems, but are not limited to these.

[0171] Examples of gas sterilization devices include: air purifiers, air conditioners, ceiling fans, vacuum cleaners for floors or bedding, bedding dryers, shoe dryers, washing machines, clothes dryers, indoor germicidal lamps, warehouse ventilation systems, shoe cabinets, wardrobes, etc., but are not limited to these.

[0172] Examples of solid sterilization devices (including surface sterilization devices) include: vacuum packaging machines, belt conveyors, sterilization devices for hand tools used in medical / dental / hairdressing / beauty salons, toothbrushes, toothbrush cases, chopstick cases, cosmetic bags, drain covers, toilet spot cleaners, toilet seats, etc., but are not limited to these.

[0173] 2. Second Implementation Method

[0174] A nitride semiconductor element according to a second embodiment of this disclosure will be described. The nitride semiconductor element of this embodiment is, for example, a light-emitting element.

[0175] The following explains the case where nitride semiconductor devices are used as light-emitting devices.

[0176] (2.1) Composition of light-emitting element

[0177] The light-emitting element of this embodiment includes an Al-containing nitride semiconductor substrate and a semiconductor stack disposed on the nitride semiconductor substrate. The semiconductor stack includes: a first conductivity type cladding layer comprising a first conductivity type nitride semiconductor; a light-emitting layer disposed on the first conductivity type cladding layer and formed of a nitride semiconductor comprising one or more quantum wells; and a second conductivity type cladding layer disposed on the light-emitting layer and formed of a second conductivity type Al-containing nitride semiconductor. The surface of the second conductivity type cladding layer has a vortex-shaped stepped structure with platforms and height differences, other than a straight line when viewed from above.

[0178] The light-emitting element of this embodiment differs from the laser diode of the first embodiment in that it does not have a first conductive waveguide layer and a second conductive waveguide layer. Furthermore, in the light-emitting element of this embodiment, the second conductive cladding layer is sometimes used as a barrier layer.

[0179] Furthermore, the light-emitting element of this embodiment has a different configuration of the first conductive coating layer than that of the laser diode of the first embodiment. Therefore, the first and second conductive coating layers of the light-emitting element will be described in detail below.

[0180] It should be noted that, except for the first conductive coating layer, the other layers, namely the nitride semiconductor substrate, the buffer layer and the light-emitting layer, are the same as the layers described in the first embodiment, and therefore their descriptions are omitted.

[0181] <First conductive coating layer>

[0182] The first conductivity cladding layer is a nitride semiconductor layer containing Al and Ga. For example, the first conductivity cladding layer is composed of Al... a Ga (1-a)N (0 < a < 1) is formed, for example, preferably from Al. a Ga (1-a) N (0.7≤a≤1) is formed.

[0183] The first conductive coating layer is preferably formed of an n-type semiconductor.

[0184] In addition, the thickness T0 of the first conductive coating layer is preferably 3300×a-2100nm or more and 15700×a-10100nm or less (a is the proportion of Al atoms when the total number of Group III atoms of the nitride semiconductor constituting the first conductive coating layer is set to 1).

[0185] Furthermore, the resistivity of the first conductive coating layer is preferably 1×10⁻⁶. -3 Ωcm or more and 5×10 -3 Below Ωcm.

[0186] Apart from this, the configuration has the same configuration as the first conductive coating layer described in the first embodiment.

[0187] <Second conductive coating layer>

[0188] In the light-emitting element, instead of a second conductive cladding layer with a gradually changing Al composition, an electron blocking layer with a constant Al composition is disposed on the light-emitting layer, and a second conductive contact layer with a gradually changing Al composition is disposed on the electron blocking layer. This electron blocking layer and the second conductive contact layer with a gradually changing Al composition serve as cladding layers.

[0189] At this point, by growing the electron blocking layer at a lower temperature than before, the same effect as in the laser diode of the first embodiment is achieved: both the effect of suppressing the degradation of the electron blocking layer and the second conductive contact layer and the effect of improving the injection efficiency of charge carriers into the light-emitting layer are obtained. When the electron blocking layer and the second conductive contact layer are considered as the second conductive cladding layer, the inflow of the organometallic gas is temporarily stopped before the growth of the electron blocking layer to interrupt the growth of the nitride semiconductor layer, allowing only a portion of the electron blocking layer to grow at a low temperature. As a result, similar to the second conductive cladding layer of the laser diode, the concentration distribution of carbon or oxygen is discontinuously reduced, and hydrogen is locally present at the interface of the electron blocking layer on the light-emitting layer side, resulting in a light-emitting element containing more impurities in the electron blocking layer than before.

[0190] In addition, after the growth of the electron blocking layer and before the growth of the second conductive contact layer, the inflow of organometallic gas is temporarily stopped to interrupt the growth of the nitride semiconductor layer. This allows the region of the second conductive cladding layer (the layer that combines the electron blocking layer and the second conductive contact layer) that is separated from the nitride semiconductor substrate by the thickness of the electron blocking layer to contain hydrogen at a higher concentration than other regions.

[0191] The thickness of the electron blocking layer is preferably 10 nm or more and 15 nm or less. That is, in the light-emitting element, the region in which the concentration distribution of carbon or oxygen contained in the electron blocking layer decreases discontinuously is preferably present in the region of the electron blocking layer from the substrate side, which is 10 nm or more and 15 nm or less.

[0192] It should be noted that the light-emitting element in this embodiment differs from the laser diode in the first embodiment in that it does not have a first conductive waveguide layer and a second conductive waveguide layer. Therefore, it is difficult to evaluate α, which indirectly represents potential fluctuations. This is because when it is desired to evaluate α, which indirectly represents potential fluctuations, the quantized light-emitting layer is excited, resulting in incorrect results. However, by forming a nitride semiconductor layer under the same conditions as in the first embodiment, it is possible to form a nitride semiconductor layer that has the same indirect representation of potential fluctuations, α.

[0193] 3. Specific examples of nitride semiconductor devices

[0194] The following is for reference Figures 4-7 The figures below provide a more detailed description of the nitride semiconductor device of this embodiment. It should be noted that the detailed configuration of each layer in the following examples is as described above.

[0195] (3.1) First example

[0196] Figure 4 This is a cross-sectional schematic diagram of laser diode 1, used as the first example. (See attached diagram.) Figure 4 As shown, the laser diode 1 includes a substrate 11, a semiconductor stack 10 disposed on the substrate, a first electrode 13, and a second electrode 14. The semiconductor stack 10 includes a first conductivity type cladding layer 101 having an n-type conductivity type, a first conductivity type waveguide layer 102, a light-emitting layer 103, a second conductivity type waveguide layer 104, and a second conductivity type cladding layer 105 having a p-type conductivity type.

[0197] (3.2) Second case

[0198] Figure 5 This is a cross-sectional schematic diagram of laser diode 2 as a second example. (See attached diagram.) Figure 5 As shown, the laser diode 2 includes a substrate 11, a buffer layer 12, a semiconductor stack 10 disposed on the substrate 11 (buffer layer 12), a first electrode 13, and a second electrode 14. The semiconductor stack 10 includes a first conductivity type cladding layer 101 having an n-type conductivity type, a first conductivity type waveguide layer 102, a light-emitting layer 103, a second conductivity type waveguide layer 104, and a second conductivity type cladding layer 105 having a p-type conductivity type.

[0199] That is, laser diode 2 differs from laser diode 1 in that it has a buffer layer 12.

[0200] (3.3) Third case

[0201] Figure 6 This is a cross-sectional schematic diagram of laser diode 3, which is the third example. Figure 6 As shown, the laser diode 3 includes a substrate 11, a buffer layer 12, a semiconductor stack 10 disposed on the substrate, a first electrode 13, and a second electrode 14. The semiconductor stack 10 includes a first conductivity type cladding layer 101 having an n-type conductivity type, a first conductivity type waveguide layer 102, a light-emitting layer 103, a second conductivity type waveguide layer 104, a second conductivity type cladding layer 105 having a p-type conductivity type, and a contact layer 106.

[0202] That is, laser diode 3 differs from laser diode 1 in that it has a contact layer 106.

[0203] It should be noted that the laser diode disclosed herein may also be configured to include the buffer layer 12 described in the second example and the contact layer 106 described in the third example.

[0204] (3.4) Fourth case

[0205] Figure 7 This is a cross-sectional schematic diagram of the light-emitting element 4, which is used as the first example. (See attached diagram.) Figure 7 As shown, the light-emitting element 4 includes a substrate 11, a semiconductor stack 10 disposed on the substrate, a first electrode 13, and a second electrode 14. The semiconductor stack 10 includes a first conductivity type cladding layer 101 having an n-type conductivity type, a light-emitting layer 103, and a second conductivity type cladding layer 105 having a p-type conductivity type. It should be noted that in the light-emitting element 4, an electron blocking layer and a second conductivity type contact layer are provided to serve as the second conductivity type cladding layer 105.

[0206] That is, the light-emitting element 4 differs from the laser diode 1 in that it does not have a first conductive waveguide layer 102 and a second conductive waveguide layer 104. In addition, the light-emitting element 4 differs from the laser diode 1 in that it has an electron blocking layer and a second conductive contact layer, which together function as a second conductive cladding layer 105.

[0207] It should be noted that the light-emitting element disclosed herein may also be configured to include the buffer layer 12 described in the second example.

[0208] 4. Effects

[0209] The above-mentioned nitride semiconductor device has the following effects.

[0210] (1) The nitride semiconductor device of this disclosure comprises an Al-containing nitride semiconductor substrate and a semiconductor stack disposed on the nitride semiconductor substrate. The semiconductor stack comprises: a first conductivity type cladding layer comprising a first conductivity type nitride semiconductor; a light-emitting layer disposed on the first conductivity type cladding layer and formed of a nitride semiconductor comprising one or more quantum wells; and a second conductivity type cladding layer disposed on the light-emitting layer and formed of a second conductivity type Al-containing nitride semiconductor. The surface of the second conductivity type cladding layer has a vortex-shaped stepped structure with a platform and height difference, other than a straight line when viewed from above.

[0211] Therefore, it is possible to better combine the effects of suppressing the degradation of the second conductive coating layer in the laser diode and improving the injection efficiency of charge carriers into the light-emitting layer.

[0212] (2) In the nitride semiconductor device disclosed herein, it is preferred that the height of the vortex-shaped step structure is 0.2 nm or more and 0.4 nm or less.

[0213] As a result, the current injection efficiency is further improved, resulting in a greater effect of suppressing the degradation of the second conductive coating layer.

[0214] (3) In the nitride semiconductor device of this disclosure, the preferred distribution density of the vortex-shaped step structure is 1×10⁻⁶. 7 cm -2 Above and 5×10 8 cm -2 the following.

[0215] As a result, the current injection efficiency is further improved, resulting in a greater effect of suppressing the degradation of the second conductive coating layer.

[0216] (4) In the method for manufacturing the nitride semiconductor stack disclosed herein, a first conductivity type cladding layer comprising a first conductivity type nitride semiconductor is formed on a nitride semiconductor substrate containing Al, a light-emitting layer is formed on the first conductivity type cladding layer by a nitride semiconductor comprising one or more quantum wells, a portion of a second conductivity type cladding layer comprising a second conductivity type nitride semiconductor is formed under conditions of a wafer temperature of 900°C or higher and 1000°C or lower and a reactor pressure of 15 mbar or higher and 350 mbar or lower, and the remaining portion of the second conductivity type cladding layer is formed under conditions of a wafer temperature of 1030°C or higher and 1100°C or lower and a reactor pressure of 15 mbar or higher and 350 mbar or lower, thereby forming a semiconductor stack on the nitride semiconductor substrate.

[0217] Thus, a portion of the second conductive coating can be formed with more carbon or oxygen than the remainder of the second conductive coating, and the second conductive coating can simultaneously suppress degradation and improve implantation efficiency.

[0218] (5) In the method for manufacturing the nitride semiconductor stack disclosed herein, it is preferable that the reactor pressure when forming a portion of the second conductive coating layer is 15 mbar or more and 100 mbar or less.

[0219] Therefore, a portion of the second conductive coating can be formed in a manner that contains more carbon or oxygen than the remainder of the second conductive coating, thereby further improving the degradation suppression effect and injection efficiency of the second conductive coating.

[0220] (6) In the method for manufacturing the nitride semiconductor stack disclosed herein, it is preferable to allow the organometallic gas to flow in during the formation of the first conductive coating layer, the light-emitting layer, and the second conductive coating layer, and to temporarily stop the flow of the organometallic gas after the formation of the light-emitting layer and before the formation of a portion of the second conductive coating layer, and to temporarily stop the flow of the organometallic gas after the formation of a portion of the second conductive coating layer and before the formation of the remaining portion of the second conductive coating layer.

[0221] This allows the growth of the layer containing the nitride semiconductor to be temporarily interrupted, thereby enabling hydrogen and silicon to be locally present at the interface on the substrate side of the second conductive coating layer, further improving the effect of suppressing the degradation of the second conductive coating layer and improving the efficiency of carrier injection into the light-emitting layer.

[0222] Example

[0223] <Sample 1>

[0224] The laser diode of this disclosure will now be described through embodiments and comparative examples. It should be noted that the laser diode of this disclosure is not limited to these embodiments.

[0225] A (0001) plane AlN single crystal substrate with a thickness of 550 μm was used as the substrate.

[0226] Next, an AlN layer as a homoepitaxial layer was formed on the substrate. The AlN layer was formed at 1200°C with a thickness of 500 nm. At this time, the ratio of the supply rate of the Group III element feed gas to the supply rate of the nitrogen feed gas (V / III ratio) was 50. The growth rate of the AlN layer was 0.5 μm / hour. Trimethylaluminum (TMAl) was used as the Al feed gas. Ammonia (NH3) was used as the N feed gas.

[0227] A first conductive cladding layer was formed on the substrate. The first conductive cladding layer is an n-type AlGaN layer using Si as the dopant (Al: 75%, i.e., Al...). 0.75 Ga 0.25 The first conductive coating layer was formed at a temperature of 1050°C, a reactor pressure of 50 mbar, and a V / III ratio of 4000 to a thickness of 400 nm. The growth rate of the first conductive coating layer was 0.4 μm / hour. Trimethylaluminum (TMAl) was used as the Al raw material. Triethylgallium (TEGa) was used as the Ga raw material. Ammonia (NH3) was used as the N raw material. Silicate (SiH4) was used as the Si raw material.

[0228] Next, an n-type waveguide layer, serving as the first waveguide layer, is formed on the first conductivity cladding layer. The n-type waveguide layer is an n-type AlGaN layer using Si as the dopant (Al: 63%, i.e., Al...). 0.63 Ga 0.37 (N-layer). The n-type waveguide layer was formed at a temperature of 950°C, with the reactor pressure set at 300 mbar and the V / III ratio set at 4000, to a thickness of 40 nm. The growth rate of the n-type waveguide layer at this time was 0.35 μm / hour.

[0229] In addition, trimethylaluminum (TMAl) is used as the Al raw material. Additionally, triethylgallium (TEGa) is used as the Ga raw material. Furthermore, ammonia (NH3) is used as the N raw material.

[0230] Next, a light-emitting layer was formed on the n-type waveguide layer. The light-emitting layer was formed by depositing a multi-quantum-well structure with two cycles of stacked quantum well layers and barrier layers. Here, the quantum well layer is an AlGaN layer with a thickness of 4.5 nm (Al: 52%, i.e., Al...). 0.52 Ga 0.48 N-layer). Additionally, the barrier layer with a thickness of 6.0 nm is an AlGaN layer (Al: 63%, i.e., Al). 0.63 Ga 0.37 (N layers).

[0231] The light-emitting layer was formed at 950°C, with a reactor pressure of 300 mbar and a V / III ratio of 4000. The growth rate of the quantum well layer was 0.18 μm / hour. The growth rate of the barrier layer was 0.15 μm / hour.

[0232] Next, a p-type waveguide layer was formed on the light-emitting layer as the second waveguide layer. The p-type waveguide layer is an undoped AlGaN layer (Al: 63%, i.e., Al2O3). 0.63 Ga 0.37The p-type waveguide layer was formed at a temperature of 950°C, a reactor pressure of 300 mbar, and a V / III ratio of 4000 to a thickness of 70 nm. The growth rate of the p-type waveguide layer was 0.35 μm / hour. Trimethylaluminum (TMAl) was used as the Al raw material. Triethylgallium (TEGa) was used as the Ga raw material.

[0233] Next, a second conductivity cladding layer was formed on the p-type waveguide layer. The second conductivity cladding layer is a composition-gradient layer with a gradient Al composition. The second conductivity cladding layer consists of an AlGaN layer (interface gradient portion) with an Al composition distributed in the direction away from the substrate and varying from Al=0.63 to Al=1.0, with a layer thickness of 2.5 nm, and a p-type AlGaN layer with an Al composition distributed in the direction away from the substrate and varying from Al=1.0 to Al=0.7, with a layer thickness of 330 nm.

[0234] Before growing the second conductive coating layer, the inflow of organometallic gas was temporarily stopped, and the reactor pressure was set to 50 mbar at a temperature of 950°C under conditions of irradiation only with hydrogen and NH3. An initial layer (A) with a thickness of 72.5 nm and an Al composition of 0.63→1.0→0.95 was formed (a layer formed from the interface gradient region and a portion of the second conductive coating layer). The growth rate at this time was 0.3 μm / h to 0.5 μm / h. Here, layer (A) is a layer formed from the interface gradient region and a portion of the second conductive coating layer. In the 72.5 nm thick layer (A), the region with an Al composition of 0.63→1.0 and a thickness of 2.5 nm is the "interface gradient region," and the remaining region with an Al composition of 1.0→0.95 and a thickness of 70 nm is the "part of the second conductive coating layer." Furthermore, the "interface gradient region" is also included within the second conductive coating layer.

[0235] Next, the inflow of organometallic gas was temporarily stopped, and the reactor pressure was set to 50 mbar at a temperature of 1050 °C under irradiation only with hydrogen and NH3. A remaining layer (B) with a thickness of 257.5 nm and an Al composition of 0.98–0.7 (the remaining portion of the second conductive coating) was formed under a V / III ratio of 4000. The growth rate at this point was 0.3 μm / h to 0.5 μm / h.

[0236] Furthermore, trimethylaluminum (TMAl) is used as the Al raw material throughout the entire process. Triethylgallium (TEGa) is used as the Ga raw material. It should be noted that the interface between layer (A) and layer (B) corresponds to a region P where the impurity concentration distribution changes drastically, or to a region Q where the Al composition is discontinuous in the direction away from the substrate.

[0237] Next, a p-type contact layer, serving as the second conductivity type contact layer, is formed on the second conductivity type cladding layer. Here, the p-type contact layer is formed from an AlGaN layer and a GaN layer. The AlGaN layer is a 30 nm thick p-type nitride semiconductor layer with Mg as a dopant, an Al composition distribution varying from Al=0.7 to Al=0.4 in the direction away from the substrate. The GaN layer is formed from GaN (i.e., Al: 0%) with a thickness of 10 nm.

[0238] The second conductive contact layer was formed at a temperature of 950°C, with the reactor pressure set to 150 mbar and the V / III ratio set to 3650. The growth rate of the second conductive contact layer under these conditions was 0.2 μm / hour.

[0239] Various analyses were performed on the nitride semiconductor stack obtained through the above operations. The results showed that the Al composition at the interface between the well layer and the barrier layer in the light-emitting layer exhibited a gradient region of 0.5 nm. The α value, indirectly representing the potential fluctuation, was 146 meV.

[0240] Next, at the interface between the second conductive coating layers (A) and (B), a discontinuity in the Al composition was observed, with the initial composition of (B) being 3% higher than that of (A). Furthermore, at the interface between (A) and (B), a hydrogen concentration of 5 × 10⁻⁶ was observed. 18 cm -3 Si is 5×10 18 cm -3 At this point, the FWHM of the hydrogen peak is 7.5 nm. Similarly, in (A), compared to (B), more oxygen and carbon were detected, and the concentration distribution changed discontinuously at the interface between (A) and (B). The oxygen and carbon concentrations at this point are 3 × 10⁻⁶. 17 cm -3 and 3×10 17 cm -3 .

[0241] Furthermore, the second conductive contact layer was removed using SF6 gas, and the surface was observed. The results showed that the surface shape exhibited a hexagonal, vortex-like stepped structure with a step height of 0.3 nm and a step density of 5 × 10⁻⁶. 7 cm -2 .

[0242] The semiconductor stack formed as described above is annealed at 700°C for more than 10 minutes in an N2 atmosphere, thereby further reducing the resistance of the second conductivity contact layer. Dry etching is performed using ICP and a Cl2-containing gas, thereby forming a mesa structure that exposes the first conductivity cladding layer.

[0243] The resulting mesa structure has a length of 700 μm in the <1-100> direction and a length of 40 μm in the <11-20> direction. Here, the length in the <1-100> direction of the mesa structure is the distance between the end faces of the resonant cavity mirrors when viewed from above, and the length in the <11-20> direction is the distance between the sides of the mesa structure.

[0244] On the second conductive contact layer of the mesa structure, Ni and Au are sequentially deposited in a rectangular shape extending in the <1-100> direction to form multiple electrode metal regions, which serve as the p-type second electrode. The width of the second electrode is 5 μm, and its length is 600 μm or more. Furthermore, in the region where the n-type cladding layer of the mesa structure is exposed, V, Al, Ni, Ti, and Au are sequentially deposited in a rectangular shape extending in the <1-100> direction to form multiple electrode metal regions, which serve as the n-type first electrode. The first and second electrodes were annealed at 550°C for 60 seconds under a nitrogen atmosphere using an RTA apparatus.

[0245] Then, within the electrode metal region, the substrate is repeatedly cleaved parallel to the <11-20> direction, thereby dividing it into strips to form a monolithic laser diode. The length of the cleaved mesa structure in the <1-100> direction is 600 μm.

[0246] The laser diode obtained through this operation was subjected to current-face luminescence intensity measurement based on current injection. The results showed a threshold voltage of 8V and an oscillation threshold current of 3kA / cm. 2 The oscillation time at this point is 100 seconds.

[0247] <Sample 2> to <Sample 4>

[0248] Except for changing the Al composition of the n-type AlGaN layer, which uses Si as a dopant, as shown in Table 1, the laser diodes of samples 2 to 4 were formed by operating in the same manner as sample 1.

[0249] <Sample 5> to <Sample 8>

[0250] Except for changing the film thickness of the first conductive coating layer as shown in Table 1, the same operation as for sample 1 was performed to form laser diodes of samples 5 to 8.

[0251] <Sample 9> to <Sample 25>

[0252] Except for changing the wafer temperature and reactor pressure during the growth of the nitride semiconductor layer when forming the light-emitting layer, the first conductive waveguide layer, and the second conductive waveguide layer, as shown in Table 1, the laser diodes of samples 10 to 28 were formed by operating in the same manner as sample 1. It should be noted that the growth temperature and growth pressure listed in the light-emitting layer section of Table 1 refer to the temperatures during the formation of the light-emitting layer, the first waveguide layer, and the second waveguide layer. The α value, which indirectly represents the potential fluctuation of the first waveguide layer, is shown in Table 1.

[0253] <Sample 26> to <Sample 29>

[0254] Except for changing the wafer temperature during the growth of the nitride semiconductor layer when forming the second conductivity cladding layer, as shown in Tables 1 and 2, the same procedure was followed as for Sample 1 to form laser diodes for Samples 26 to 29. The discontinuity at the Al composition discontinuity points and the concentration of carbon or oxygen in the second conductivity cladding layer are the values ​​shown in Table 1. Furthermore, observing the surface of each sample revealed that Sample 26 formed a vortex-like step structure based on a circular shape, Sample 27 formed a circular step structure with localized angles, Sample 28 showed a vortex-like step structure based on a mixture of hexagonal and straight lines, and Sample 29 showed a straight step structure.

[0255] <Sample 30> to <Sample 32>

[0256] Except for changing the reactor pressure during nitride semiconductor layer growth when forming a portion of the substrate side of the second conductive coating layer as shown in Table 2, the same procedure as for Sample 1 was followed to form laser diodes for Samples 30 to 32. The discontinuity at the Al composition discontinuity points and the carbon or oxygen concentration contained in the second conductive coating layer are the values ​​shown in Table 2.

[0257] <Sample 33> to <Sample 35>

[0258] Except for changing the wafer temperature during the growth of the nitride semiconductor layer when forming the remaining portion of the second conductive coating layer as shown in Table 2, the same procedure was followed as for Sample 1 to form the laser diodes of Samples 33 to 35. The discontinuity at the Al composition discontinuity points and the carbon or oxygen concentration contained in the second conductive coating layer are the values ​​shown in Table 2.

[0259] <Sample 36>~<Sample 38>

[0260] Except for changing the reactor pressure during the growth of the nitride semiconductor layer when forming the remaining portion of the second conductive coating layer as shown in Table 2, the same procedure as for Sample 1 was followed to form the laser diodes of Samples 36 to 38. The discontinuity at the Al composition discontinuity points and the carbon or oxygen concentration contained in the second conductive coating layer are the values ​​shown in Table 2.

[0261] <Sample 39>~<Sample 42>

[0262] Except for changing the thickness of the remaining portion of the second conductive coating layer to alter the overall film thickness of the second conductive coating layer as shown in Table 2, the same procedure as for sample 1 was followed to form laser diodes for samples 39 to 42. The discontinuities at the Al composition discontinuities and the carbon or oxygen concentrations contained in the second conductive coating layer are the values ​​shown in Table 2.

[0263] <Sample 43>~<Sample 44>

[0264] Except for changing the thickness of the compositional gradient layer formed between the second conductive waveguide layer and the second conductive cladding layer as shown in Table 2, the same operation as for sample 1 was performed to form the laser diodes of samples 43 to 44.

[0265] <Sample 45>~<Sample 49>

[0266] The thickness of the region with reduced Al composition in a portion of the substrate side of the second conductive coating layer was changed to 30 nm, 5 nm, 2 nm, 110 nm, and 150 nm, respectively. The thickness of the remaining portion of the second conductive coating layer was also changed to make the overall film thickness of the second conductive coating layer 330 nm. Otherwise, the same procedure as for sample 1 was followed to form laser diodes of samples 45 to 49. Here, the thickness of the portion of the second conductive coating layer on the substrate side is the distance from the substrate side to the region where the Al composition is discontinuous or the carbon or oxygen concentration distribution decreases discontinuously.

[0267] <Sample 50> to <Sample 53>

[0268] Except for changing the hydrogen concentration on a portion of the substrate side of the second conductive coating by altering the growth interruption time, the same procedure as for sample 1 was followed to form laser diodes for samples 50 to 53.

[0269] <Sample 54>~<Sample 55>

[0270] Except that the growth of the nitride semiconductor layer was not interrupted before and after a portion of the substrate side where the second conductive coating layer was formed, the laser diodes of samples 54 to 55 were formed by operating in the same manner as sample 1.

[0271] <Sample 56>

[0272] When growth is interrupted, a predetermined amount of Ga is supplied to form a second conductive coating layer in such a way that there are no discontinuities of Al at the interface between a portion and the remaining portion of the substrate side of the second conductive coating layer. Otherwise, the same operation as in sample 1 is performed to form the laser diode of sample 56.

[0273] [Table 1]

[0274]

[0275] [Table 2]

[0276]

[0277] In samples 1 to 56 of Tables 1 and 2, the growth of the nitride semiconductor layer was interrupted before and after the formation of the second conductive cladding layer on a portion of the substrate side. Furthermore, compared to samples 27 and 29, which do not have such a vortex-shaped stepped structure, the laser diodes with the second conductive cladding layer having a vortex-shaped stepped structure with platforms and height differences on the surface (other than a straight line when viewed from above) exhibited lower overall threshold voltage and oscillation threshold, and longer oscillation time. This confirms that both cladding layer degradation suppression and carrier injection efficiency are achieved.

[0278] The embodiments of this disclosure have been described above. However, the above embodiments are illustrative of the apparatus and methods used to concretize the technical concept of this disclosure. The technical concept of this disclosure does not specifically specify the material, shape, structure, or arrangement of the constituent components. Various modifications can be made to the technical concept of this disclosure within the technical scope defined by the claims.

[0279] Label Explanation

[0280] 1, 2, 3 Laser diodes

[0281] 4. Light-emitting element

[0282] 10 Semiconductor stack-up

[0283] 11 base plate

[0284] 12 Buffer Layers

[0285] 13 First Electrode

[0286] 14 Second Electrode

[0287] 101 First conductive coating layer

[0288] 102 First Conductivity Waveguide Layer

[0289] 103 Emissive Layer

[0290] 104 Second Conductivity Waveguide Layer

[0291] 105 Second conductive coating layer

[0292] 106 Contact Layer

Claims

1. A method for manufacturing a nitride semiconductor laminate, wherein, A first conductivity type cladding layer comprising a first conductivity type nitride semiconductor is formed on a nitride semiconductor substrate containing Al. A light-emitting layer is formed on the first conductive coating layer by a nitride semiconductor containing one or more quantum wells. A portion of a second conductivity type cladding layer comprising a nitride semiconductor of the second conductivity type is formed under conditions of a wafer temperature of 900°C or higher and 1000°C or lower, and a reactor pressure of 15 mbar or higher and 350 mbar or lower. The remaining portion of the second conductive coating layer is formed under the conditions of a wafer temperature of 1030°C or higher and 1100°C or lower, and a reactor pressure of 15 mbar or higher and 350 mbar or lower, thereby forming a semiconductor stack on the nitride semiconductor substrate.

2. The method for manufacturing a nitride semiconductor laminate according to claim 1, wherein, The reactor pressure when forming part of the second conductive coating is above 15 mbar and below 100 mbar.

3. The method for manufacturing a nitride semiconductor laminate according to claim 1 or 2, wherein, During the formation of the first conductive coating layer, the light-emitting layer, and the second conductive coating layer, an organometallic gas is introduced. After the light-emitting layer is formed and before a portion of the second conductive coating layer is formed, the inflow of the organometallic gas is temporarily stopped. After a portion of the second conductive coating layer has been formed, and before the remaining portion of the second conductive coating layer has been formed, the inflow of the organometallic gas is temporarily stopped.

4. A method for manufacturing a nitride semiconductor device, wherein, After the semiconductor stack is formed by the manufacturing method of the nitride semiconductor stack according to any one of claims 1 to 3, Unwanted portions of each layer of the semiconductor stack are removed by etching. Electrodes are formed on the semiconductor stack, and The nitride semiconductor substrate, on which the corner layers of the semiconductor stack are formed, is divided into individual pieces by cutting.

5. A nitride semiconductor device, wherein, The nitride semiconductor device comprises: Al-containing nitride semiconductor substrates; and A semiconductor stack, wherein the semiconductor stack is disposed on the nitride semiconductor substrate. The semiconductor stack has: A first conductivity type coating layer, wherein the first conductivity type coating layer comprises a nitride semiconductor of a first conductivity type; A light-emitting layer is disposed on the first conductive cladding layer and is formed of a nitride semiconductor containing one or more quantum wells; and A second conductivity cladding layer is disposed on the light-emitting layer and is formed of an Al-containing nitride semiconductor of the second conductivity type. The surface of the second conductive coating layer has a stepped structure with platforms and height differences, which is not straight when viewed from above.

6. The nitride semiconductor device according to claim 5, wherein, The height of the vortex-shaped stepped structure is above 0.2 nm and below 0.4 nm.

7. The nitride semiconductor device according to claim 5, wherein, The distribution density of the vortex-shaped stepped structure is 1×10 7 cm -2 Above and 5×10 8 cm -2 the following.

8. The nitride semiconductor device according to claim 5, wherein, The nitride semiconductor substrate is an AlN single crystal substrate.

9. The nitride semiconductor device according to claim 5, wherein, The first conductive coating layer is made of Al a Ga (1-a) N (0.65 < a ≤ 0.9) is formed.

10. The nitride semiconductor device according to claim 5, wherein, The thickness of the first conductive coating layer is above 250 nm and below 800 nm.

11. The nitride semiconductor device according to claim 5, wherein, The nitride semiconductor device comprises: A first conductive waveguide layer is disposed between the first conductive cladding layer and the light-emitting layer to confine light within the light-emitting layer; and A second conductive waveguide layer is disposed between the second conductive cladding layer and the light-emitting layer to confine light within the light-emitting layer.

12. The nitride semiconductor device according to claim 5, wherein, The nitride semiconductor device includes a second conductivity contact layer disposed on the second conductivity cladding layer and formed of a GaN-containing nitride semiconductor. The second conductive coating layer contains Al d Ga (1-d) N (0.1≤d≤1) has a compositional gradient where the Al composition d decreases as the distance from the nitride semiconductor substrate decreases, and the film thickness is less than 500 nm.

13. The nitride semiconductor device according to claim 12, wherein, The second conductive coating layer has a compositional gradient in which the Al composition d decreases in the range of 1 to 0.7 as it moves away from the nitride semiconductor substrate.

14. The nitride semiconductor device according to claim 9 or 12, wherein, The thickness of the second conductive coating layer is above 250 nm and below 400 nm.

15. The nitride semiconductor device according to claim 5, wherein, The thickness T0 of the first conductive coating layer is greater than 3300×a-2100nm and less than 15700×a-10100nm (a is the proportion of Al atoms when the total number of Group III atoms constituting the nitride semiconductor of the first conductive coating layer is set to 1).

16. The nitride semiconductor device according to claim 15, wherein, The resistivity of the first conductive coating layer is 1×10⁻⁶. -3 Ωcm or more and 5×10 -3 Below Ωcm.

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