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

Abstract

The purpose of the present invention is to both suppress deterioration of a clad layer and improve carrier injection efficiency in a nitride semiconductor element. A nitride semiconductor laminate serving as a nitride semiconductor element, obtained by: forming a first-conductivity-type clad layer containing a first-conductivity-type nitride semiconductor on a nitride semiconductor substrate that contains Al; forming a light-emitting layer, on the first-conductivity-type clad layer, from a nitride semiconductor including one or more quantum wells; forming a portion of a second-conductivity-type clad layer containing a second-conductivity-type nitride semiconductor under the conditions of the wafer temperature being 900-1000°C and the reactor pressure being 15-350 mbar; forming the remainder of the second-conductivity-type clad layer under the condition of the wafer temperature being 1030-1100°C and the reactor pressure being 15-350 mbar; and forming a semiconductor laminated part on the nitride semiconductor substrate.

Description

Method for manufacturing nitride semiconductor laminate and nitride semiconductor device, and nitride semiconductor device

[0001] The present disclosure relates to a nitride semiconductor stack, a method for manufacturing a nitride semiconductor device, and a nitride semiconductor device.

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

[0003] Zhang et al. , Applied Physics Express 12, 124003 (2019)

[0004] The nitride semiconductor devices such as the laser diodes described above can improve the injection efficiency of carriers (electrons or holes), but have not been able to sufficiently suppress deterioration of the cladding layer. An object of the present disclosure is to provide a nitride semiconductor stack, a method for manufacturing a nitride semiconductor device, and a nitride semiconductor device that can achieve both suppression of cladding layer deterioration and improvement of carrier injection efficiency.

[0005] In order to solve the above-described problems, a method for manufacturing a nitride semiconductor stack according to one aspect of the present disclosure includes forming a first-conductivity-type cladding layer including a nitride semiconductor of a first conductivity type on a nitride semiconductor substrate including Al, forming a light-emitting layer on the first-conductivity-type cladding layer using a nitride semiconductor including one or more quantum wells, forming a part of a second-conductivity-type cladding layer including a nitride semiconductor of a second conductivity type under conditions where the wafer temperature is from 900°C to 1000°C and the reactor pressure is from 15 mbar to 350 mbar, and forming the remaining part of the second-conductivity-type cladding layer under conditions where the wafer temperature is from 1030°C to 1100°C and the reactor pressure is from 15 mbar to 350 mbar, thereby forming a semiconductor stack on the nitride semiconductor substrate.

[0006] Furthermore, in a method for manufacturing a nitride semiconductor device according to another aspect of the present disclosure, after forming a semiconductor laminate portion by the above-described method for manufacturing a nitride semiconductor laminate, unnecessary portions of each layer of the semiconductor laminate portion are removed by etching, electrodes are formed on the semiconductor laminate portion, and the nitride semiconductor substrate on which each layer of the semiconductor laminate portion has been formed is divided into individual pieces by dicing.

[0007] A nitride semiconductor device according to another aspect of the present disclosure includes a nitride semiconductor substrate containing Al and a semiconductor laminate portion disposed on the nitride semiconductor substrate. The semiconductor laminate portion includes a first-conductivity-type cladding layer containing a nitride semiconductor of a first conductivity type, a light-emitting layer disposed on the first-conductivity-type cladding layer and formed of a nitride semiconductor including one or more quantum wells, and a second-conductivity-type cladding layer disposed on the light-emitting layer and formed of a nitride semiconductor containing Al. The surface of the second-conductivity-type cladding layer has a spiral-shaped step-terrace structure having terraces and steps that are not linear in plan view. Note that the above-described summary of the invention does not list all of the features of the invention according to the present disclosure.

[0008] According to the present disclosure, it is possible to provide a nitride semiconductor stack that can suppress deterioration of the cladding layer while improving carrier injection efficiency, a method for manufacturing a nitride semiconductor device, and a nitride semiconductor device.

[0009] FIG. 1 is a graph showing an example of the Al composition in a nitride semiconductor device according to an embodiment of the present disclosure; FIG. 2 is an AFM photograph showing the structure of the upper surface of a second conductivity type cladding layer of a nitride semiconductor device according to an embodiment of the present disclosure; FIG. 3 is an AFM photograph showing the structure of the upper surface of a second conductivity type cladding layer of a nitride semiconductor device according to an embodiment of the present disclosure; FIG. 4 is a schematic plan view showing an example of the structure of a nitride semiconductor device according to an embodiment of the present disclosure; FIG. 5 is a schematic cross-sectional view showing an example of the structure of a nitride semiconductor device according to an embodiment of the present disclosure; FIG. 6 is a schematic cross-sectional view showing an example of the structure of a nitride semiconductor device according to an embodiment of the present disclosure;

[0010] Hereinafter, nitride semiconductor devices according to the present disclosure will be described through embodiments, but the following embodiments do not limit the scope of the claimed invention. Furthermore, not all of the combinations of features described in the embodiments are necessarily essential to the solution of the invention. In the following description, "up" and "down" do not necessarily refer to the vertical direction relative to the ground. In other words, the "up" and "down" directions are not limited to the direction of gravity. "Up" and "down" are merely convenient expressions for specifying the relative positional relationship of surfaces, films, substrates, etc., and do not limit the technical concept of the present invention. For example, if the paper is rotated 180 degrees, "up" becomes "down" and "down" becomes "up."

[0011] 1. First Embodiment A nitride semiconductor device according to a first embodiment of the present disclosure will be described. The nitride semiconductor device according to this embodiment is, for example, a laser diode. Below, a case where the nitride semiconductor device is a laser diode will be described.

[0012] (1.1) Configuration of the Laser Diode The laser diode according to this embodiment includes a nitride semiconductor substrate containing Al and a semiconductor laminate disposed on the nitride semiconductor substrate. The semiconductor laminate includes a first-conductivity-type cladding layer containing a nitride semiconductor of a first conductivity type, 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 nitride semiconductor containing Al of a second conductivity type. The surface of the second-conductivity-type cladding layer has a spiral-shaped step-terrace structure having terraces and steps that are not linear in plan view. Each layer of the laser diode is described in detail below.

[0013] <Nitride Semiconductor Substrate> The nitride semiconductor substrate (hereinafter sometimes referred to as substrate) contains a nitride semiconductor containing Al. The nitride semiconductor containing Al is, for example, AlN. That is, the substrate is preferably an AlN single crystal substrate. Furthermore, the nitride semiconductor containing Al is not limited to AlN, and may be, for example, AlGaN. For example, when the substrate is a nitride semiconductor single crystal substrate such as AlN or AlGaN, the difference in lattice constant with the nitride semiconductor layer formed on the substrate becomes small, and threading dislocations can be reduced by growing the nitride semiconductor layer in a lattice-matched system. The threading dislocation density of the substrate is 5×10 ４ cm －２ In particular, from the viewpoint of improving the emission intensity and reducing the oscillation threshold current, the threading dislocation density is preferably 1×10 ３ cm －２ 1x10 or more ４ cm －２ It is more preferable that the substrate is formed on a heterosubstrate as long as it contains a nitride semiconductor containing Al. For example, sapphire (Al ２ O ３ ) AlN may be grown on the substrate.

[0014] Here, the "comprises" in the expression "comprises a nitride semiconductor" means that the nitride semiconductor is mainly contained in the layer, but this expression also includes cases where other elements are contained. Specifically, this expression also includes cases where the composition of this layer is slightly changed by adding a small amount of an element other than the nitride semiconductor (for example, a few percent or less of an element such as Ga (when Ga is not the main element), In, As, P, or Sb). In expressions of the composition of other layers, the wording "comprises" has the same meaning. Furthermore, the small amount of elements contained is not limited to the above.

[0015] The substrate preferably has a thickness of 100 μm or more and 600 μm or less, for example. The plane orientation may be c-plane (0001), a-plane (11-20), or m-plane (10-10), with a c-plane (0001) substrate being more preferred. Furthermore, the substrate may be formed on a plane tilted at some angle (for example, −4° to 4°, preferably −0.4° to 0.4°) from the normal direction of the c-plane (0001), but is not limited thereto.

[0016] <Buffer Layer> A buffer layer may be formed on the substrate, i.e., between the substrate and the first conductivity type cladding layer. The buffer layer is preferably formed on the entire surface of the substrate. By providing the buffer layer, a nitride semiconductor layer with small lattice constant differences and thermal expansion coefficient differences and few defects is formed on the buffer layer. The buffer layer is preferably a nitride semiconductor layer containing Al, and is formed of a nitride semiconductor such as AlN or AlGaN. The buffer layer may also contain impurities such as C, Si, Fe, or Mg.

[0017] The buffer layer has a thickness of, for example, several μm. Specifically, the thickness of the buffer layer is preferably greater than 10 nm and less than 10 μm. When the buffer layer is thicker than 10 nm, the crystallinity of the nitride semiconductor such as AlN is increased. Furthermore, when the buffer layer is thinner than 10 μm, cracks are less likely to occur in the buffer layer formed by crystal growth over the entire surface of the wafer.

[0018] <First Conductivity-Type Cladding Layer> The first conductivity-type cladding layer is formed on a substrate. Here, for example, the term "on" in the expression "the first conductivity-type cladding layer is formed on a substrate" means that the first conductivity-type cladding layer is formed on one side of the substrate. The above expression also includes cases where another layer exists between the substrate and the first conductivity-type cladding layer. The term "on" has a similar meaning in other relationships between layers. For example, the expression "the second conductivity-type cladding layer is formed on the first conductivity-type waveguide layer" also includes cases where a second conductivity-type cladding layer is formed on the first conductivity-type waveguide layer described below via an electron blocking layer. In addition, in the description of this embodiment, the terms "first conductivity type" and "second conductivity type" refer to semiconductors exhibiting different conductivity types; for example, if one is n-type conductivity, the other is p-type conductivity.

[0019] The first conductivity type cladding layer is a nitride semiconductor layer containing Al and Ga. The first conductivity type cladding layer is, for example, Al ａ Ga （１－ａ） N (0<a<1). This makes it possible to enhance the crystallinity of the light-emitting layer and improve the light-emitting efficiency when a material corresponding to the band gap energy in the deep ultraviolet region is formed as the light-emitting layer. From the viewpoint of realizing high light-emitting efficiency, the nitride semiconductor constituting the first conductivity type cladding layer is preferably a mixed crystal of AlN and GaN. Furthermore, from the viewpoint of growing the first conductivity type cladding layer and each layer formed above with complete strain relative to the substrate, the first conductivity type cladding layer is preferably Al ａ Ga （１－ａ） It is more preferable that the crystalline silicon be formed by N (0.65<a≦0.9).

[0020] The first-conductivity-type cladding layer may be a gradient layer in which the Al composition increases with increasing distance from the substrate, for purposes such as controlling longitudinal conductivity. In this case, the above-mentioned limitation on the Al composition may be the Al composition obtained by averaging the Al composition at positions in the thickness direction within the first-conductivity-type cladding layer over the thickness of the first-conductivity-type cladding layer. When the first-conductivity-type cladding layer is an n-type conductive semiconductor layer, it may contain impurities such as Group V elements other than N, such as P, As, and Sb, as well as C, H, F, O, Mg, and Si, but the types of impurity elements are not limited to these. From the viewpoints of reducing electrical resistance and ease of obtaining raw materials, the impurity contained in the first-conductivity-type cladding layer is preferably Si, and the impurity concentration is 5×10 １８ cm －３ 5x10 or more １９ cm －３ The resistivity of the first conductivity type cladding layer is preferably 1×10 －３ Ωcm or more 5 x 10 －３ It is preferable that the resistivity is Ωcm or less, which allows efficient carrier injection.

[0021] From the viewpoints of lattice relaxation within the first conductivity type cladding layer and film resistance, the first conductivity type cladding layer preferably has a layer thickness of 250 nm or more and 800 nm or less, and more preferably has a layer thickness of 300 nm or more and 450 nm or less.

[0022] <Light Emitting Layer> The light emitting layer is a layer of a nitride semiconductor containing Al and Ga. From the viewpoint of realizing high light emitting efficiency, the nitride semiconductor contained in the light emitting layer is preferably a mixed crystal of AlN or GaN, for example. ｂ Ga （１－ｂ） The light-emitting layer may contain impurities such as group V elements other than N, such as P, As, and Sb, and C, H, F, O, Mg, and Si, but the types of impurity elements are not limited to these.

[0023] The light-emitting layer may have either a multiple quantum well structure or a single quantum well structure. The number of quantum well structures is preferably between 1 and 5, depending on the longitudinal conductivity of the first and second conductivity type cladding layers.

[0024] In the laser diode of this embodiment, α, which indirectly represents the potential fluctuation of the nitride semiconductor layer, is preferably 130 meV or more and 350 meV or less. The nitride semiconductor layer represented by such α may be not only the light-emitting layer but also a first-conductivity-type waveguide layer or a second-conductivity-type waveguide layer described below. When α of the light-emitting layer, the first-conductivity-type waveguide layer, or the second-conductivity-type waveguide layer is 130 meV or more and 350 meV or less, localized carriers recombine efficiently, thereby improving the light-emitting efficiency. Here, the "potential fluctuation of the nitride semiconductor layer" is an index for specifying the distribution state of Ga in the in-plane direction of the nitride semiconductor layer, and the "α indirectly representing the potential fluctuation" is an index indicating deviation from the alloy uniformity in the in-plane direction of the nitride semiconductor layer. When the above-mentioned α is 30 meV (or so), it indicates that Ga is uniformly distributed in the in-plane direction of the nitride semiconductor layer, i.e., Al and Ga are uniformly arranged. Such potential fluctuations appear in the half-width of the emission spectrum of the nitride semiconductor layer. That is, the closer the nitride semiconductor constituting the nitride semiconductor layer is to a completely uniform crystal, the narrower the half-width of the emission spectrum. On the other hand, the possible values ​​of the half-width of the emission spectrum also vary depending on the Al composition of the nitride semiconductor. Therefore, the potential fluctuations of the nitride semiconductor layer are evaluated using α, which expresses the deviation from the half-width of the emission spectrum in a uniform state at each Al composition. The Al composition x of the nitride semiconductor layer and the half-width FWHM of the emission spectrum at the emission wavelength can be expressed by the formula FWHM (meV) = αx + 10 meV. In this case, a large α indicates that the state is far from uniform, that is, Ga and the like are segregated or localized.

[0025] Furthermore, the thickness of the region where the Al concentration profile changes gradually at the interface between the well layer and the barrier layer in the light-emitting layer is preferably 0.3 nm to 0.6 nm, which can improve carrier confinement and emission intensity.

[0026] <Waveguide Layer> From the viewpoint of light confinement as a laser diode, the laser diode of this embodiment may include waveguide layers formed above and below the light-emitting layer so as to sandwich the light-emitting layer and having the effect of confining light emitted from the light-emitting layer within the light-emitting layer. The waveguide layers are preferably composed of two layers: a first-conductivity-type waveguide layer disposed between the first-conductivity-type cladding layer and the light-emitting layer, and a second-conductivity-type waveguide layer disposed between the second-conductivity-type cladding layer and the light-emitting layer. That is, the laser diode of this embodiment may include, for example, a first-conductivity-type waveguide layer disposed between the first-conductivity-type cladding layer and the light-emitting layer to confine light to the light-emitting layer, and a second-conductivity-type waveguide layer disposed between the second-conductivity-type cladding layer and the light-emitting layer to confine light to the light-emitting layer.

[0027] From the viewpoint of light confinement, the waveguide layer is preferably a nitride semiconductor containing Al and Ga, which has a band gap higher in energy than the light emitting layer. The waveguide layer preferably has an Al composition and film thickness that increase the overlap between the electric field intensity distribution of the light existing in the device and the light emitting layer. From the viewpoint of carrier confinement in the light emitting layer, the light emitting layer is preferably made of Al. ｂ Ga （１－ｂ） N (0<b<1), and the waveguide layer is Al ｃ Ga （１－ｃ） When N (0<c<1), it is more preferable that b<c and c≧b+0.05. For example, in the case of an emission layer having an emission wavelength of 265 nm, it is preferable that b is 0.52 and c is 0.57 or more. Furthermore, from the viewpoints of light confinement and layer resistance, it is preferable that the total film thickness of the waveguide layer (the total film thickness of the first conductivity type waveguide layer and the second conductivity type waveguide layer) is 70 nm or more and 150 nm or less.

[0028] The waveguide layer may contain impurities such as P, As, Sb, and other V group elements other than N, C, H, F, O, Mg, and Si, but the types of impurity elements are not limited to these. From the viewpoint of reducing electrical resistance and the ease of obtaining raw materials, the impurity contained in the first conductivity type waveguide layer is preferably Si, and the impurity concentration is 5×10 １８ cm －３ 5x10 or more １９ cm －３It is preferable that:

[0029] The Al composition of each of the first-conductivity-type waveguide layer and the second-conductivity-type waveguide layer is preferably uniform in the thickness direction, but is not limited to this. To avoid light absorption by a metal (e.g., a second electrode) present above the second-conductivity-type cladding layer described below, the Al composition of the second-conductivity-type waveguide layer may be higher than the Al composition of the first-conductivity-type waveguide layer. For the same purpose, the thickness of the second-conductivity-type waveguide layer may be thicker than the thickness of the first waveguide.

[0030] <Second Conductivity Type Cladding Layer> The second conductivity type cladding layer is formed on the light emitting layer and is a nitride semiconductor layer containing Al and Ga and having second conductivity type. ｄ Ga （１－ｄ） N (0.1≦d≦1). Specifically, the second conductivity type cladding layer is formed on the second conductivity type waveguide layer. This allows the second conductivity type cladding layer to easily lattice match with the light emitting layer or the waveguide layer, and makes it possible to suppress the threading dislocation density.

[0031] The second conductivity type cladding layer is not particularly limited as long as it has sufficient conductivity to inject carriers (electrons or holes) into the light-emitting layer and can increase the overlap between the electric field intensity distribution of the optical mode existing in the device and the light-emitting layer (i.e., increase light confinement). The second conductivity type cladding layer may be, for example, p-type AlGaN doped with Mg. The second conductivity type cladding layer may also contain impurities such as P, As, Sb, and other Group V elements other than N, as well as C, H, F, O, Mg, and Si, but the types of impurity elements are not limited to these.

[0032] From the viewpoint of more efficient injection of carriers into the light-emitting layer, the second conductivity type cladding layer has a composition gradient such that the Al composition d decreases with increasing distance from the substrate. ｄ Ga （１－ｄ）The second-conductivity-type cladding layer is a compositionally graded layer formed of N (0.1≦d≦1), but in a portion of the second-conductivity-type cladding layer, the Al composition d increases with increasing distance from the substrate. The second-conductivity-type cladding layer preferably has a composition gradient in which the Al composition d decreases in the range of 1 to 0.7 with increasing distance from the nitride semiconductor substrate. The profile (gradient) of the Al composition d in the second-conductivity-type cladding layer may decrease continuously or intermittently. Here, "intermittently decreasing" means that the second-conductivity-type cladding layer includes a portion in which the Al composition d is constant (constant in the film thickness direction). In other words, the second-conductivity-type cladding layer may include a portion in which the Al composition d does not decrease with increasing distance from the substrate (a portion in which the Al composition d is constant or increases).

[0033] The thickness of the second conductivity type cladding layer is preferably 500 nm or less from the viewpoint of lattice matching, and more preferably 250 nm to 500 nm from the viewpoint of optical confinement.

[0034] FIG. 1 shows the Al composition (shown by bold lines) and impurity composition (shown by solid lines) in each layer of a laser diode. Note that FIG. 1 illustrates an example of a structure without a buffer layer. As shown in FIG. 1 , the second-conductivity-type cladding layer has a composition gradient such that the Al composition d decreases with increasing distance from the substrate. A portion of the second-conductivity-type cladding layer is doped with impurities such as carbon or oxygen. The impurity is also doped into, for example, an interface gradient portion on the second-conductivity-type waveguide layer where the Al composition increases, resulting in a discontinuous increase in concentration profile at the starting point of the composition gradient layer (the interface on the second-conductivity-type waveguide layer side). Conventionally, second-conductivity-type cladding layers are often formed of nitride semiconductors with little impurity doping, for purposes such as suppressing impurity diffusion and improving injection efficiency. However, by including a large amount of impurities in a portion of the second-conductivity-type cladding layer, it is possible to simultaneously suppress degradation and improve injection efficiency in the second-conductivity-type cladding layer.

[0035] The second-conductivity-type cladding layer preferably has at least one region in which the concentration profile of carbon or oxygen contained in the second-conductivity-type cladding layer changes discontinuously with increasing distance from the substrate. That is, the second-conductivity-type cladding layer preferably has a region in which the impurity concentration profile is convex in the direction of increasing concentration. By having such a discontinuous region, the second-conductivity-type cladding layer has a portion that suppresses deterioration of the second-conductivity-type cladding layer and a remaining portion that improves the injection efficiency of carriers (electrons or holes) into the light-emitting layer. In this case, the carbon or oxygen concentration profile in the second-conductivity-type cladding layer has a steep slope, which improves the injection efficiency of carriers into the light-emitting layer, and the second-conductivity-type cladding layer can simultaneously suppress deterioration of the second-conductivity-type cladding layer and improve the injection efficiency of carriers into the light-emitting layer. Generally, if the impurity concentration profile has a region that is convex in the direction in which the concentration increases, this is disadvantageous in terms of the efficiency of carrier injection into the light-emitting layer. However, depending on the thickness of the second cladding layer, providing a region in which the carbon or oxygen concentration profile slopes at a steep gradient can be advantageous in terms of the overall efficiency of carrier injection into the light-emitting layer.

[0036] Here, "a region in which the concentration profile discontinuously decreases with increasing distance from the substrate (nitride semiconductor substrate) at least at one point" refers to a region in which the impurity concentration in a certain region (the impurity concentration measured at a measurement point in the region) differs by two or more times from the surrounding impurity concentration (the impurity concentration measured at a measurement point in an adjacent region). For example, as shown in Figure 1, there is a region P in which the impurity concentration profile changes abruptly.

[0037] As described above, the second-conductivity-type cladding layer has a region P where the impurity concentration profile decreases discontinuously. The region P where the concentration profile decreases discontinuously is preferably present in a region of 1 nm to 110 nm, more preferably 5 nm to 110 nm, from the substrate side of the second-conductivity-type cladding layer. This makes it possible to suppress deterioration of the second-conductivity-type cladding layer without impeding the improvement of the efficiency of carrier injection into the light-emitting layer.

[0038] In addition, in the second conductivity type cladding layer, the region closer to the substrate than the region P where the impurity concentration profile discontinuously decreases is Al ｅ Ga （１－ｅ） It is preferable that the second conductive type cladding layer is made of N (0.8≦e≦1.0). This makes it possible to suppress deterioration of the second conductive type cladding layer without impeding the improvement of the efficiency of carrier injection into the light emitting layer. The carbon concentration in the region of the second conductive type cladding layer closer to the substrate than the region P where the impurity concentration profile decreases discontinuously is 1×10 １７ cm －３ 1x10 or more １８ cm －３ Similarly, the oxygen concentration in the second conductivity type cladding layer in the region closer to the substrate than the region P where the impurity concentration profile decreases discontinuously is preferably 1×10 １７ cm －３ 1x10 or more １８ cm －３ It is preferable that the thickness of the cladding layer is less than 100 nm. This allows a layer that is effective in suppressing deterioration of the second conductivity type cladding layer and a layer that is effective in improving the efficiency of carrier injection into the light emitting layer to be formed in a good condition. Therefore, it is possible to more effectively achieve both the effect of suppressing deterioration of the second conductivity type cladding layer in the laser diode and the effect of improving the efficiency of carrier injection into the light emitting layer.

[0039] As described above, the second conductivity type cladding layer of the embodiment shown in FIG. ｄ Ga （１－ｄ） The second conductivity type cladding layer has a composition gradient in which the Al composition d decreases with increasing distance from the nitride semiconductor substrate (0.1≦d≦1). At least a portion of the second conductivity type cladding layer is a composition discontinuous region Q in which the Al composition is discontinuous in the direction away from the substrate, and in the composition discontinuous region Q, the Al composition d increases with increasing distance from the substrate. As such, the second conductivity type cladding layer has a composition discontinuous region Q, so that the laser diode can achieve both the effect of suppressing deterioration of the second conductivity type cladding layer and the effect of improving the efficiency of carrier injection into the light emitting layer.

[0040] The compositional discontinuous region Q is preferably present in a region of 1 nm to 110 nm from the nitride semiconductor substrate side of the second conductivity-type cladding layer, and more preferably in a region of 5 nm to 110 nm. That is, the starting point of the compositional discontinuous region Q preferably coincides with the starting point of region P. By providing the compositional discontinuous region Q on the nitride semiconductor substrate side of the second conductivity-type cladding layer, deterioration of the second conductivity-type cladding layer can be suppressed without impeding the improvement of carrier injection efficiency into the light-emitting layer. Furthermore, the compositional discontinuous region Q preferably has a compositional gradient in which the Al composition d increases from 0.002 to 0.05 with increasing distance from the substrate. Such a compositional gradient in the compositional discontinuous region Q results in the formation of a layer that is effective in suppressing deterioration of the second conductivity-type cladding layer and a layer that is effective in improving carrier injection efficiency into the light-emitting layer. This allows the laser diode to more effectively achieve both the effect of suppressing deterioration of the second conductivity-type cladding layer and the effect of improving carrier injection efficiency into the light-emitting layer.

[0041] In addition, the interface of the second conductivity type cladding layer on the substrate side (i.e., the interface with the second conductivity type waveguide layer) contains 1×10 hydrogen. １７ cm －３ 5x10 or more １９ cm －３ It is preferable that the second conductivity type cladding layer contains hydrogen at a concentration higher than that of other regions of the second conductivity type cladding layer. Although the second conductivity type cladding layer contains a trace amount of hydrogen overall, the second conductivity type cladding layer of the laser diode of this embodiment includes a region (the said region) containing a high concentration of hydrogen. This allows the laser diode to compensate for point defects and achieve both the effect of suppressing deterioration of the second conductivity type cladding layer and the effect of improving the efficiency of carrier injection into the light emitting layer.

[0042] The region containing hydrogen at a higher concentration than other regions of the second conductivity-type cladding layer is preferably a region of the second conductivity-type cladding layer that is 1 nm or more and 110 nm or less from the substrate side, and more preferably a region of 5 nm or more and 110 nm or less. This allows point defects to be compensated for, and deterioration of the second conductivity-type cladding layer to be suppressed without impeding improvement in the efficiency of carrier injection into the light-emitting layer. Furthermore, the half-width of the hydrogen concentration profile in the region containing hydrogen at a higher concentration than other regions of the second conductivity-type cladding layer is preferably 5 nm or more and 10 nm or less. This allows point defects to be effectively compensated for, and improvement in the efficiency of carrier injection into the light-emitting layer.

[0043] The second conductive type cladding layer has a substrate-side interface with silicon of 1×10 １７ cm －３ 5x10 or more １９ cm －３ At least a portion of the second conductivity type cladding layer may contain silicon at a concentration higher than that of other regions of the second conductivity type cladding layer. The region of the second conductivity type cladding layer that contains silicon at a concentration higher than that of other regions of the second conductivity type cladding layer is preferably a region of the second conductivity type cladding layer that is 1 nm or more and 110 nm or less from the substrate side, and more preferably a region of 5 nm or more and 110 nm or less.

[0044] As shown in FIG. 2A , the surface of the second-conductivity-type cladding layer described above has a spiral-shaped step-terrace structure having terraces and steps that are not linear in plan view. One example of a spiral-shaped step-terrace structure is a hexagonal base with one side of its outline gradually shortening. Other examples of a spiral-shaped step-terrace structure are a circular base with a gradually shortening radius, or a hexagonal / linear hybrid base with gradually shortening sides. For comparison, FIG. 3 shows a step-terrace structure having linear terraces and steps in plan view. This allows for both suppressing deterioration of the second-conductivity-type cladding layer in a laser diode and improving the efficiency of carrier injection into the light-emitting layer. By growing and forming such a second-conductivity-type cladding layer at a lower temperature than conventional methods (as will be described in detail later), the linear step-terrace structure transitions to a spiral step-terrace structure. 2A is an atomic force microscope (AFM) photograph showing a spiral step-terrace structure, and FIG. 2B is a scanning electron microscope (SEM) photograph showing a circular step-terrace structure. Compared to when a circular or linear step-terrace structure is formed on the surface of the second conductivity-type cladding layer, when the spiral step-terrace structure is formed, a higher effect of improving the luminous efficiency of the second conductivity-type cladding layer can be obtained. This is thought to be because Ga segregates during the growth process of the film with the spiral step-terrace structure, improving the current injection efficiency.

[0045] The height of the spiral step-terrace structure is preferably 0.2 nm or more and 0.4 nm or less. The distribution density of the spiral step-terrace structure is preferably 1×10 ７ cm －２ 5x10 or more ８ cm －２ This makes it possible to obtain a higher effect of suppressing deterioration of the second conductivity type cladding layer and an improved current injection efficiency.

[0046] In addition, if a nitride semiconductor layer having a spiral step-terrace structure is formed and then a nitride semiconductor layer is deposited by a conventional method to form a second conductivity type cladding layer, the spiral step-terrace structure also appears on the surface of the second conductivity type cladding layer. Therefore, by observing the surface shape of the second conductivity type cladding layer, the spiral step-terrace structure on the surface of the second conductivity type cladding layer can be confirmed. In addition, if a second conductivity type contact layer (described later) is formed on the second conductivity type cladding layer, the spiral step-terrace structure does not appear on the surface of the second conductivity type contact layer. However, for example, if sulfur hexafluoride (SF ６ By removing only the second conductivity type contact layer using a gas or the like to expose the second conductivity type contact layer and observing it with an SEM or the like, the spiral step-terrace structure on the surface of the second conductivity type cladding layer can be confirmed.

[0047] <Interface Inclined Portion> The laser diode according to this embodiment has an Al ｇ Ga （１－ｇ） The nitride semiconductor layer may have an inclined interface portion containing N (0.1≦g≦1) and in which the Al composition g increases with increasing distance from the nitride semiconductor substrate. By providing the inclined interface portion as in this embodiment, the electrolysis is alleviated, improving the degradation suppression effect. Furthermore, the film thickness of the inclined interface portion is preferably 2 nm to 5 nm, and more preferably 2 nm to 3 nm. In this case, the degradation suppression effect is further improved.

[0048] <Second-Conduction-Type Contact Layer> The semiconductor laminate portion of the laser diode of this embodiment may further include a second-conduction-type contact layer disposed on the second-conduction-type cladding layer. The nitride semiconductor constituting the second-conduction-type contact layer is preferably formed of, for example, GaN, AlN, or InN, or a mixed crystal containing these, and more preferably a nitride semiconductor containing GaN.

[0049] In the case of a p-type contact layer, the second conductivity type contact layer may contain impurities such as P, As, Sb, and other V group elements other than N, and C, H, F, O, Mg, Si, and Be. From the viewpoint of versatility of source gases, the impurity contained in the second conductivity type contact layer is preferably Mg. From the viewpoint of reducing contact resistance, the concentration of Mg is preferably 8×10 １９ cm －３ 5x10 or more ２１ cm －３ Preferably, it is 5×10 or less. ２０ cm －３ 5x10 or more ２１ cm －３ More preferably, it is:

[0050] The thickness of the second conductivity type contact layer is preferably 1 nm or more and 20 nm or less. The thinner the second conductivity type contact layer, the more efficient the carrier injection into the light emitting layer becomes, and the thicker the second conductivity type contact layer, the more efficient the carrier injection into the light emitting layer becomes.

[0051] <Electron Blocking Layer> The semiconductor laminate of the laser diode of this embodiment may further include an electron blocking layer above the light-emitting layer, the electron blocking layer having a band gap larger than that of the light-emitting layer. The electron blocking layer may be provided, for example, on the light-emitting layer, or may be provided inside the second-conductivity-type waveguide layer, between the second-conductivity-type waveguide layer and the light-emitting layer, or between the second-conductivity-type waveguide layer and the second-conductivity-type cladding layer. The thickness of the electron blocking layer is preferably 30 nm or less, and more preferably 20 nm or less, to facilitate quantum penetration of carriers (holes) through the electron blocking layer.

[0052] <Electrodes> The laser diode can emit light or oscillate by injecting a current through a second electrode disposed on the second conductivity type cladding layer and a first electrode disposed on the first conductivity type cladding layer. In this case, the first electrode is formed so as to be in electrical contact with the first conductivity type cladding layer, and the second electrode is formed so as to be in electrical contact with the second conductivity type cladding layer.

[0053] The first electrode can be disposed, for example, on the back side of the substrate. Alternatively, the first electrode can be disposed on the first-conductivity-type cladding layer exposed by removing layers above the first-conductivity-type cladding layer of the semiconductor laminate by, for example, chemical etching or dry etching. In other words, the first electrode is disposed on a region of the first-conductivity-type cladding layer that does not form a mesa structure.

[0054] When the first conductive type clad layer is an n-type clad layer, the first electrode is made of a metal such as Al, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, or Zr, or a mixed crystal thereof, or ITO or Ga ２ O ３ When the first conductive type cladding layer is a p-type cladding layer, the first electrode is made of a metal such as Ni, Au, Pt, Ag, Rh, Pd, Pt, Cu, Al, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Co, Ir, Zr, or a mixed crystal thereof, or ITO or Ga ２ O ３ It is formed from a conductive oxide such as the above.

[0055] When the second conductive type clad layer is an n-type clad layer, the second electrode is made of a metal such as Al, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, or Zr, or a mixed crystal thereof, or ITO or Ga ２ O ３ When the second conductive type cladding layer is a p-type cladding layer, the second electrode is made of a metal such as Ni, Au, Pt, Ag, Rh, Pd, Pt, Cu, Al, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Co, Ir, Zr, or a mixed crystal thereof, or ITO or Ga ２ O ３ It is formed from a conductive oxide such as the above.

[0056] The placement area and shape of the first electrode and the second electrode are not limited as long as electrical contact is obtained with the first conductivity type clad layer and the second conductivity type clad layer (or the second conductivity type contact layer if a second conductivity type contact layer is provided).

[0057] (1.2) Methods for Manufacturing Nitride Semiconductor Stack and Nitride Semiconductor Device The laser diode, which is the nitride semiconductor device of this embodiment, can be manufactured by singulating a nitride semiconductor stack manufactured through the steps of forming each nitride semiconductor layer on a substrate. Below, we will explain a method for manufacturing a nitride semiconductor stack and a method for manufacturing a laser diode as an example of a method for manufacturing a nitride semiconductor device.

[0058] (1.2.1) Method for Manufacturing Nitride Semiconductor Stack (Formation of Substrate) The substrate is formed by a general substrate growth method such as a vapor phase growth method such as sublimation or hydride vapor phase epitaxy (HVPE), or a liquid phase growth method.

[0059] (Formation of Semiconductor Laminate Layer) Each layer of the semiconductor laminate layer formed on the substrate can be formed by, for example, molecular beam epitaxy (MBE), hydride vapor phase epitaxy (HVPE), metal organic chemical vapor deposition (MOCVD), etc. Here, among the layers formed on the substrate, the nitride semiconductor layer can be formed from, for example, an Al source containing trimethylaluminum (TMAl), a Ga source containing trimethylgallium (TMGa) or triethylgallium (TEGa), or ammonia (NH ３ The film can be formed using a nitrogen source containing nitrogen.

[0060] A semiconductor laminate layer is formed on a substrate. At this time, a metal-organic gas is flowed into a semiconductor laminate layer formation space. First, a first conductivity type cladding layer including a first conductivity type nitride semiconductor is formed on the substrate.

[0061] Next, a first conductivity type waveguide layer made of a nitride semiconductor such as AlGaN is formed on the first conductivity type cladding layer, and then a light emitting layer made of a nitride semiconductor (such as AlGaN) including one or more quantum wells is formed on the light emitting layer, followed by a second conductivity type waveguide layer made of a nitride semiconductor such as AlGaN.

[0062] In this case, the first conductivity type waveguide layer, the light emitting layer, and the second conductivity type waveguide layer are preferably formed under conditions that satisfy the relationship -2Tw + 2050 < Vw < -2Tw + 2350 (850°C < Tw < 970°C), where Tw is the wafer temperature and Vw is the reactor pressure. This makes it possible to form a light emitting layer in which Ga is non-uniformly distributed in the surface direction of the nitride semiconductor layer. Similarly, it is possible to form a first conductivity type waveguide and a second conductivity type waveguide in which Ga is non-uniformly distributed in the surface direction of the nitride semiconductor layer. This localizes carriers, thereby increasing the recombination rate and improving the light emission efficiency.

[0063] Next, a second-conductivity-type cladding layer is formed on the second-conductivity-type waveguide layer. First, before forming a portion of the second-conductivity-type cladding layer, the inflow of the metalorganic gas is temporarily stopped to interrupt the growth of the nitride semiconductor layer and change the film formation conditions. Next, it is preferable to change the conditions to a wafer temperature of 900°C or higher and 1000°C or lower, a reactor pressure of 15 mbar or higher and 350 mbar or lower, and then resume the inflow of the metalorganic gas to form a portion of the second-conductivity-type cladding layer using the second-conductivity-type nitride semiconductor.

[0064] After forming a portion of the second conductivity type cladding layer and before forming the remaining portion of the second conductivity type cladding layer, the inflow of the metalorganic gas is again temporarily stopped to interrupt the growth of the nitride semiconductor layer and change the film formation conditions, then the wafer temperature is changed to 1030°C or higher and 1100°C or lower, and the reactor pressure is changed to 15 mbar or higher and 350 mbar or lower, and the inflow of the metalorganic gas is resumed to form the remaining portion of the second conductivity type cladding layer.

[0065] Forming the first-conductivity-type cladding layer, the first-conductivity-type waveguide layer, the light-emitting layer, and the second-conductivity-type waveguide layer in the above manner increases the carrier recombination rate and reduces point defects in each layer, thereby suppressing degradation and improving light-emitting efficiency. Furthermore, by setting the wafer temperature during formation of a portion of the second-conductivity-type cladding layer lower than the wafer temperature during formation of the remaining portion of the second-conductivity-type cladding layer, it is possible to form at least one region in which the carbon or oxygen concentration profile in the portion of the second-conductivity-type cladding layer and the remaining portion of the second-conductivity-type cladding layer discontinuously decreases with increasing distance from the substrate. That is, the portion of the second-conductivity-type cladding layer can be formed to contain more carbon or oxygen than the remaining portion of the second-conductivity-type cladding layer. This allows for both suppression of degradation and improved injection efficiency in the second-conductivity-type cladding layer. Furthermore, by setting the reactor pressure when forming a portion of the second conductivity type cladding layer to a lower pressure than the reactor pressure when forming the remaining portion of the second conductivity type cladding layer, the portion of the second conductivity type cladding layer can be formed to contain a larger amount of carbon or oxygen as an impurity than the remaining portion of the second conductivity type cladding layer.

[0066] Furthermore, by temporarily stopping the flow of the metalorganic gas before forming a part of the second conductive type cladding layer, hydrogen and silicon are localized at the interface of the second conductive type cladding layer on the substrate side. This can be achieved by using, for example, hydrogen gas (H ２ This is because, when a second conductivity type cladding layer is used, hydrogen (H) is likely to be localized in the uppermost layer of the nitride semiconductor layer where growth is interrupted (for example, the interface between the second conductivity type waveguide layer and the second conductivity type cladding layer and a part of the second conductivity type cladding layer). This allows the laser diode to further improve the effect of suppressing deterioration of the second conductivity type cladding layer and the effect of improving the efficiency of carrier injection into the light emitting layer.

[0067] Conventionally, when the growth of a nitride semiconductor layer is interrupted, some elements (e.g., Ga in the case of AlGaN) are removed, so interruption of growth has been avoided as much as possible. However, by interrupting growth and actively introducing hydrogen, point defects at the interface are localized at the interface between the second conductivity type waveguide layer and the second conductivity type cladding layer and in part of the second conductivity type cladding layer. III -H ３ By compensating for this, it is possible to improve the degradation suppression effect. Furthermore, conventionally, when the second conductivity type cladding layer is a p-type semiconductor layer, it is preferable that it does not contain silicon, which would be an n-type impurity. However, by actively introducing silicon by interrupting growth and localizing silicon derived from the raw materials and susceptor at the interface between the second conductivity type waveguide layer and the second conductivity type cladding layer and in part of the second conductivity type cladding layer, it is possible to compensate for point defects at the interface and improve the degradation suppression effect.

[0068] As described above, in this embodiment, the wafer temperature during the formation of a portion of the second-conductivity-type cladding layer is set lower than the wafer temperature during the formation of the remaining portion of the second-conductivity-type cladding layer, thereby forming at least one region in which the carbon or oxygen concentration profile in the portion of the second-conductivity-type cladding layer and the remaining portion of the second-conductivity-type cladding layer discontinuously decreases with increasing distance from the substrate. However, the manufacturing method is not limited to this. For example, the flow rate of the metal-organic gas may be intentionally changed during the formation of the second-conductivity-type cladding layer to form a region in which the carbon or oxygen concentration profile discontinuously decreases with increasing distance from the substrate.

[0069] Furthermore, if necessary, an intermediate layer may be formed between the second conductivity type cladding layer and the second conductivity type waveguide layer using a nitride semiconductor such as AlGaN, a second conductivity type contact layer may be provided on the second conductivity type cladding layer using a nitride semiconductor containing GaN or the like, or an electron blocking layer may be formed above the light emitting layer.

[0070] (1.2.2) Manufacturing Method of Nitride Semiconductor Device (Laser Diode) (Mesa Structure Formation) A laser diode is manufactured through a process of forming a semiconductor laminate by etching away unnecessary portions of each layer of a semiconductor laminate formed on a substrate (mesa structure formation process). Removal of unnecessary portions of each layer of the semiconductor laminate can be performed by, for example, inductively coupled plasma (ICP) etching. In the mesa structure formation process, unnecessary portions of each layer of the conductor laminate are removed by etching, thereby exposing a portion of the first conductivity type cladding layer.

[0071] (Electrode Formation) Laser diodes can also be manufactured through a process of forming electrodes. Electrodes such as the first electrode and the second electrode can be formed by various methods, such as resistance heating evaporation, electron gun evaporation, or sputtering, in which metal is evaporated by electron beam evaporation (EB) techniques, but are not limited to these methods. Each electrode can be formed as a single layer or as a multi-layer laminate. Furthermore, each electrode can be heat-treated in an oxygen, nitrogen, or air atmosphere after the metal layer is formed.

[0072] (Singulation) Finally, the substrate on which each layer has been formed through the above-described steps is diced into individual pieces to manufacture nitride semiconductor devices (laser diodes).

[0073] Specifically, a first electrode is formed on the surface of the first conductivity type cladding layer. The second electrode is formed on the top layer (e.g., the second conductivity type cladding layer) of a mesa structure that forms part of the semiconductor laminate. The formed electrode is alloyed by heating with a rapid thermal annealing (RTA) device, which is a heat treatment using an infrared lamp, or by laser annealing, which is a heat treatment using a laser pulse, to obtain contact with the semiconductor laminate. The alloying method is not particularly limited as long as sufficient contact with the semiconductor laminate is obtained. Thus, a laser diode manufactured by the nitride semiconductor device manufacturing method according to this embodiment can improve carrier injection efficiency and increase light emission intensity.

[0074] (1.3) Method for Measuring the Physical Properties of a Laser Diode The physical properties of the laser diode described above can be measured as follows.

[0075] (Layer Thickness Measurement Method) The layer thickness of each layer constituting a laser diode can be measured by cutting out a predetermined cross section perpendicular to the substrate, observing this cross section with a transmission electron microscope (TEM), and using the TEM's length measurement function. The measurement method involves first observing a cross section perpendicular to the main surface of the laser diode substrate using a TEM. Specifically, for example, within a TEM image showing a cross section perpendicular to the main surface of the laser diode substrate, an observation width of 2 μm or more is set in a direction parallel to the main surface of the substrate. Within this observation width, contrast is observed at the interface between two layers with different compositions, so the thickness up to this interface is observed in a continuous observation region 200 nm wide. The layer thickness of each layer can be obtained by calculating the average thickness of each layer included in this 200 nm wide observation region from five locations arbitrarily selected from the above-mentioned observation width of 2 μm or more.

[0076] (Measurement of Impurity Concentration and Doping Concentration) The dopant and impurity concentrations contained in each layer constituting a laser diode can be measured by secondary ion mass spectrometry (SIMS). When measuring the dopant and impurity concentrations contained in each layer using SIMS after processing into a device, the measurement can be performed after removing the electrodes by chemical etching or physical polishing. The dopant and impurity concentrations contained in each layer can also be measured by sputtering from the substrate side where no electrodes are formed. Specifically, SIMS measurement is performed under the measurement conditions provided by Evans Analytical Group (EAG). A cesium (Cs) ion beam with an energy of 14.5 keV is used to sputter the sample during measurement.

[0077] (Method for Measuring Atomic Concentration of Each Layer) One method for measuring the atomic concentration of each layer constituting a laser diode is reciprocal space mapping (RSM) using X-ray diffraction (XRD). Specifically, the lattice relaxation rate relative to the underlayer and the Al composition can be obtained by analyzing reciprocal lattice mapping data near the diffraction peak obtained using an asymmetric plane as the diffraction plane. Examples of the diffraction plane include the (10-15) plane and the (20-24) plane.

[0078] Furthermore, layers or regions that do not provide sufficient reflection intensity by XRD, such as the light-emitting layer, the gradient layer, and hillocks formed in each layer, can be measured by X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDX), and electron energy-loss spectroscopy (EELS).

[0079] EELS analyzes the composition of a sample by measuring the energy lost by an electron beam as it passes through the sample. Specifically, for example, the energy loss spectrum of the transmitted electron beam is measured and analyzed for a thin-sectioned sample used in TEM observations. The position of a peak that appears around 20 eV in energy loss varies depending on the composition of each layer, and the composition can be determined from the peak position.

[0080] In the same manner as in the method for calculating layer thickness by TEM observation described above, the Al composition of each layer is obtained by calculating the average value of the Al composition in an observation width of 200 nm from five points arbitrarily selected from an observation region of 2 μm or more.

[0081] EDX measures and analyzes characteristic X-rays generated by an electron beam in a thinned sample used in the above-mentioned TEM observation, etc. In the same manner as the method for calculating layer thickness using TEM observation described above, the Al composition of each layer is obtained by calculating the average value of the Al composition in an observation width of 200 nm from five points arbitrarily selected from an observation region of 2 μm or more.

[0082] XPS allows for depth-wise evaluation by performing XPS measurements while performing sputter etching using an ion beam. While Ar+ is typically used as the ion beam, other ion species, such as Ar cluster ions, can be used as long as they can be irradiated by the etching ion gun installed in the XPS instrument. The XPS peak intensities of Al, Ga, and N are measured and analyzed to obtain the depth-wise distribution of the Al composition in each layer. Instead of sputter etching, the laser diode can be polished obliquely so that a cross section perpendicular to the main surface of the substrate is enlarged and exposed, and the exposed cross section can be measured by XPS.

[0083] The composition of each layer can be measured not only by XPS but also by Auger Electron Spectroscopy (AES). In this case, the composition can be measured by performing Auger Electron Spectroscopy on a cross section exposed by sputter etching or angled polishing. The composition of each layer can also be measured by SEM-EDX measurement of a cross section exposed by angled polishing.

[0084] (Method for Measuring Potential Fluctuation) α, which indirectly represents potential fluctuation, is calculated using the Al composition x of the nitride semiconductor layer and the full width at half maximum FWHM at the emission wavelength, using the formula FWHM (meV) = αx + 10 meV. Specifically, FWHM is obtained from the emission spectrum obtained by performing photoluminescence measurement on the nitride semiconductor layer. α can also be obtained 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 band gap of the nitride semiconductor layer to be excited. For example, a 213 nm YAG triple-power laser is used. More accurate values ​​can be obtained by measuring while cooling the sample to 10 K or less. Furthermore, if a layer with a smaller band gap than the nitride semiconductor layer to be excited exists, it can be removed by etching or the like to measure the specific layer. Specifically, if a light-emitting layer exists on a first-conductivity-type waveguide layer, the quantized light-emitting layer is excited by the excitation light, so an accurate value can be obtained by removing the light-emitting layer by etching before measuring the first-conductivity-type waveguide layer.

[0085] (Method for Measuring Surface Profile) Examples of methods for measuring the surface profile of the second conductivity-type cladding layer include a scanning electron microscope (SEM) and atomic force microscopy (AFM). Specifically, the surface of the second conductivity-type cladding layer is observed using a scanning electron microscope SU9000 manufactured by Hitachi High-Tech Corporation at an acceleration voltage of 30 kV. At this time, the surface profile of the second conductivity-type cladding layer can be clearly observed by increasing the magnification to 10K to 50K. Under these conditions, the number of spiral step-terrace structures contained within the observation area is counted, and the value obtained by dividing the number by the area is taken as the density of the spiral step-terrace structures. The step height of the spiral step-terrace structures on the surface of the second conductivity-type cladding layer can be measured using an AFM. Specifically, the observation is performed using a scanning probe microscope manufactured by Hitachi High-Tech Corporation. A 2 μm square area is observed using the AFM mode during observation with the scanning probe microscope. The step height can be calculated from the obtained AFM gain.

[0086] (Application Fields of Nitride Semiconductor Devices) The laser diode according to the present disclosure can be applied to devices in, for example, the fields of medicine and life science, the environment, industry and manufacturing, lifestyle and home appliances, agriculture, and other fields. The laser diode can be applied to devices for synthesizing and decomposing pharmaceuticals or chemical substances, devices for sterilizing liquids, gases, and solids (containers, food, medical equipment, etc.), devices for cleaning semiconductors, etc., devices for modifying the surface of films, glass, metals, etc., exposure devices for manufacturing semiconductors, FPDs (Flat Panel Displays), PCBs (Printed Wiring Boards), and other electronic products, printing and coating devices, adhesive and sealing devices, transfer and molding devices for films, patterns, mockups, etc., and devices for measuring and inspecting banknotes, wounds, blood, chemical substances, etc.

[0087] Examples of liquid sterilization devices include, but are not limited to, 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 and flow piping for water servers, stationary water purifiers, portable water purifiers, water supply units, hot water heaters, wastewater treatment devices, garbage disposals, toilet drain traps, washing machines, dialysis water sterilization modules, peritoneal dialysis connector sterilizers, and disaster water storage systems.

[0088] Examples of gas sterilizers include, but are not limited to, air purifiers, air conditioners, ceiling fans, floor or bedding vacuum cleaners, futon dryers, shoe dryers, washing machines, clothes dryers, indoor germicidal lamps, storage ventilation systems, shoe boxes, dressers, etc. Examples of solid sterilizers (including surface sterilizers) include, but are not limited to, vacuum packers, belt conveyors, hand tool sterilizers for medical, dental, barber, and beauty salon use, toothbrushes, toothbrush holders, chopstick cases, cosmetic pouches, drain covers, toilet washer, toilet lids, etc.

[0089] 2. Second Embodiment A nitride semiconductor device according to a second embodiment of the present disclosure will be described. The nitride semiconductor device according to this embodiment is, for example, a light emitting device. Below, a case where the nitride semiconductor device is a light emitting device will be described.

[0090] (2.1) Configuration of Light-Emitting Device The light-emitting device according to this embodiment includes a nitride semiconductor substrate containing Al and a semiconductor laminate portion disposed on the nitride semiconductor substrate. The semiconductor laminate portion includes a first-conductivity-type cladding layer containing a nitride semiconductor of a first conductivity type, a light-emitting layer disposed on the first-conductivity-type cladding layer and formed of a nitride semiconductor including one or more quantum wells, and a second-conductivity-type cladding layer disposed on the light-emitting layer and formed of a nitride semiconductor containing Al. The surface of the second-conductivity-type cladding layer has a spiral-shaped step-terrace structure having terraces and steps that are not linear in plan view.

[0091] The light-emitting device of this embodiment differs from the laser diode of the first embodiment in that it does not include a first-conductivity-type waveguide layer and a second-conductivity-type waveguide layer. Furthermore, in the light-emitting device of this embodiment, the second-conductivity-type cladding layer may be used as a barrier layer. Furthermore, the light-emitting device of this embodiment has a different configuration from the first-conductivity-type cladding layer of the laser diode of the first embodiment. Therefore, the first-conductivity-type cladding layer and the second-conductivity-type cladding layer of the light-emitting device will be described in detail below. Note that the layers other than the first-conductivity-type cladding layer, i.e., 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 will not be described here.

[0092] <First Conductivity Type Cladding Layer> The first conductivity type cladding layer is a layer of a nitride semiconductor containing Al and Ga. The first conductivity type cladding layer is, for example, Al ａ Ga （１－ａ） N (0<a<1), for example, Al ａ Ga （１－ａ） The first conductivity type cladding layer is preferably formed of N (0.7≦a≦1). The first conductivity type cladding layer is preferably formed of an n-type semiconductor. The thickness T0 of the first conductivity type cladding layer is preferably 3300×a−2100 nm or more and 15700×a−10100 nm or less (a is the ratio of Al atoms when the total number of group III atoms in the nitride semiconductor constituting the first conductivity type cladding layer is 1). Furthermore, the resistivity of the first conductivity type cladding layer is preferably 1×10 －３ Ωcm or more 5 x 10 －３ The resistivity is preferably Ωcm or less. The other configurations are the same as those of the first conductivity type cladding layer described in the first embodiment.

[0093] <Second-Conduction-Type Cladding Layer> In the light-emitting device, instead of a second-conduction-type cladding layer with a graded Al composition, an electron blocking layer with a constant Al composition is provided on the light-emitting layer, and a second-conduction-type contact layer with a graded Al composition is provided on the electron blocking layer. The electron blocking layer and the second-conduction-type contact layer with a graded Al composition function as cladding layers. By growing the electron blocking layer at a lower temperature than conventional methods, the effects of suppressing deterioration of the electron blocking layer and the second-conduction-type contact layer and improving the carrier injection efficiency into the light-emitting layer can be achieved, as in the laser diode according to the first embodiment. If the electron blocking layer and the second-conduction-type contact layer are considered to be the second-conduction-type 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, and only a portion of the electron blocking layer is grown at a low temperature. As a result, similar to the second-conduction-type cladding layer of a laser diode, the carbon or oxygen concentration profile decreases discontinuously, hydrogen is localized at the interface of the electron blocking layer on the light-emitting layer side, and a light-emitting device is obtained in which the electron blocking layer contains more impurities than conventional devices. Furthermore, by temporarily stopping the inflow of the metal-organic gas after the growth of the electron blocking layer and before the growth of the second conductivity type contact layer to interrupt the growth of the nitride semiconductor layer, it becomes possible to make the region of the second conductivity type cladding layer (the layer combining the electron blocking layer and the second conductivity type contact layer) that is away from the nitride semiconductor substrate side by the thickness of the electron blocking layer contain hydrogen at a higher concentration than other regions.

[0094] 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 where the concentration profile of carbon or oxygen contained in the electron blocking layer discontinuously decreases is preferably present in a region of the electron blocking layer that is 10 nm or more and 15 nm or less from the substrate side.

[0095] Unlike the laser diode according to the first embodiment, the light-emitting device according to this embodiment does not include a first-conductivity-type waveguide layer and a second-conductivity-type waveguide layer. Therefore, it is difficult to evaluate α, which indirectly represents potential fluctuation. This is because, when attempting to evaluate α, which indirectly represents potential fluctuation, the quantized light-emitting layer is excited, preventing accurate results from being obtained. However, by forming a nitride semiconductor layer under the same conditions as those of the first embodiment, it is possible to form a nitride semiconductor layer having an α that indirectly represents a similar potential fluctuation.

[0096] 3. Specific Examples of Nitride Semiconductor Devices The nitride semiconductor devices of the present embodiment will be described in more detail below with reference to Figures 4 to 7. The detailed configuration of each layer in each of the following examples is as described above.

[0097] (3.1) First Example Fig. 4 is a schematic cross-sectional view of a laser diode 1 according to a first example. As shown in Fig. 4, the laser diode 1 includes a substrate 11, a semiconductor laminate 10 disposed on the substrate, a first electrode 13, and a second electrode 14. The semiconductor laminate 10 includes a first conductivity type cladding layer 101 having an n-type conductivity, 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.

[0098] (3.2) Second Example Fig. 5 is a cross-sectional schematic diagram of a laser diode 2 as a second example. As shown in Fig. 5, the laser diode 2 includes a substrate 11, a buffer layer 12, a semiconductor laminate 10 disposed on the substrate 11 (buffer layer 12), a first electrode 13, and a second electrode 14. The semiconductor laminate 10 includes a first conductivity type cladding layer 101 having an n-type conductivity, 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. That is, the laser diode 2 differs from the laser diode 1 in that it includes the buffer layer 12.

[0099] (3.3) Third Example FIG. 6 is a cross-sectional schematic diagram of a laser diode 3 according to a third example. As shown in FIG. 6, the laser diode 3 includes a substrate 11, a buffer layer 12, a semiconductor laminate 10 disposed on the substrate, a first electrode 13, and a second electrode 14. The semiconductor laminate 10 includes a first conductivity-type cladding layer 101 having an n-type conductivity, 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, and a contact layer 106. That is, the laser diode 3 differs from the laser diode 1 in that it includes the contact layer 106. Note that the laser diode of the present disclosure may include the buffer layer 12 described in the second example and the contact layer 106 described in the third example.

[0100] (3.4) Fourth Example FIG. 7 is a cross-sectional schematic diagram of a light-emitting element 4 according to a first example. As shown in FIG. 7, the light-emitting element 4 includes a substrate 11, a semiconductor laminate 10 disposed on the substrate, a first electrode 13, and a second electrode 14. The semiconductor laminate 10 includes a first-conductivity-type cladding layer 101 having n-type conductivity, a light-emitting layer 103, and a second-conductivity-type cladding layer 105 having p-type conductivity. The light-emitting element 4 includes an electron blocking layer and a second-conductivity-type contact layer, which function as the second-conductivity-type cladding layer 105. That is, the light-emitting element 4 differs from the laser diode 1 in that it does not include the first-conductivity-type waveguide layer 102 and the second-conductivity-type waveguide layer 104. The light-emitting element 4 also differs from the laser diode 1 in that it includes an electron blocking layer and a second-conductivity-type contact layer, which function as the second-conductivity-type cladding layer 105. The light-emitting element of the present disclosure may include the buffer layer 12 described in the second example.

[0101] 4. Effects The nitride semiconductor device described above has the following effects.

[0102] (1) A nitride semiconductor device according to the present disclosure includes a nitride semiconductor substrate containing Al and a semiconductor laminate disposed on the nitride semiconductor substrate. The semiconductor laminate includes a first-conductivity-type cladding layer containing a nitride semiconductor of a first conductivity type, a light-emitting layer disposed on the first-conductivity-type cladding layer and formed of a nitride semiconductor including one or more quantum wells, and a second-conductivity-type cladding layer disposed on the light-emitting layer and formed of a nitride semiconductor containing Al. The surface of the second-conductivity-type cladding layer has a spiral-shaped step-terrace structure having terraces and steps that are not linear in plan view. This allows the laser diode to more effectively suppress deterioration of the second-conductivity-type cladding layer and to more effectively improve the efficiency of carrier injection into the light-emitting layer.

[0103] (2) In the nitride semiconductor device of the present disclosure, the height of the spiral step-terrace structure is preferably 0.2 nm or more and 0.4 nm or less, which further improves the current injection efficiency and provides a greater effect of suppressing deterioration of the second conductivity type cladding layer.

[0104] (3) In the nitride semiconductor device of the present disclosure, the distribution density of the spiral step-terrace structure is 1×10 ７ cm －２ 5x10 or more ８ cm －２ This further improves the current injection efficiency, and a higher effect of suppressing deterioration of the second conductivity type cladding layer can be obtained.

[0105] (4) A method for manufacturing a nitride semiconductor laminate according to the present disclosure includes forming a first-conductivity-type cladding layer including a first-conductivity-type nitride semiconductor on a nitride semiconductor substrate including Al, forming a light-emitting layer on the first-conductivity-type cladding layer using a nitride semiconductor including one or more quantum wells, forming a portion of a second-conductivity-type cladding layer including a second-conductivity-type nitride semiconductor at a wafer temperature of 900° C. to 1000° C. and a reactor pressure of 15 mbar to 350 mbar, and forming the remaining portion of the second-conductivity-type cladding layer at a wafer temperature of 1030° C. to 1100° C. and a reactor pressure of 15 mbar to 350 mbar, thereby forming a semiconductor laminate on the nitride semiconductor substrate. This allows the portion of the second-conductivity-type cladding layer to contain more carbon or oxygen than the remaining portion of the second-conductivity-type cladding layer, thereby achieving both suppression of degradation and improvement of injection efficiency in the second-conductivity-type cladding layer.

[0106] (5) In the method for manufacturing a nitride semiconductor stack according to the present disclosure, the reactor pressure during the formation of a portion of the second conductivity type cladding layer is preferably 15 mbar or more and 100 mbar or less. This allows the portion of the second conductivity type cladding layer to be formed so as to contain more carbon or oxygen than the remaining portion of the second conductivity type cladding layer, thereby further improving the degradation suppression effect and injection efficiency in the second conductivity type cladding layer.

[0107] (6) In the method for manufacturing a nitride semiconductor stack according to the present disclosure, it is preferable to flow an organic metal gas during the formation of the first-conductivity-type cladding layer, the light-emitting layer, and the second-conductivity-type cladding layer, to temporarily stop the flow of the organic metal gas after forming the light-emitting layer and before forming a portion of the second-conductivity-type cladding layer, and to temporarily stop the flow of the organic metal gas after forming a portion of the second-conductivity-type cladding layer and before forming the remaining portion of the second-conductivity-type cladding layer. This temporarily stops the growth of the nitride semiconductor-containing layer, causing hydrogen and silicon to localize at the interface of the second-conductivity-type cladding layer on the substrate side, thereby further improving the effect of suppressing deterioration of the second-conductivity-type cladding layer and the effect of improving the efficiency of carrier injection into the light-emitting layer.

[0108] <Sample 1> The laser diode of the present disclosure will be described below with reference to examples and comparative examples. Note that the laser diode of the present disclosure is not limited to these examples. A (0001) plane AlN single crystal substrate having a thickness of 550 μm was used as the substrate. Next, an AlN layer, which is a homoepitaxial layer, was formed on the substrate. The AlN layer was formed to a thickness of 500 nm in an environment of 1200° C. At this time, the ratio (V / III ratio) of the supply rate of the Group III element source gas to the supply rate of the nitrogen source gas was set to 50. The growth rate of the AlN layer at this time was 0.5 μm / hr. Trimethylaluminum (TMAl) was used as the Al source. Ammonia (NH ３ ) was used.

[0109] A first conductive type cladding layer was formed on the substrate. The first conductive type cladding layer was an n-type AlGaN layer (Al: 75%, i.e., Al ０．７５ Ga ０．２５ The first conductivity type cladding layer was formed to a thickness of 400 nm under the conditions of a temperature of 1050°C, a reactor pressure of 50 mbar, and a V / III ratio of 4000. The growth rate of the first conductivity type cladding layer was 0.4 μm / hr. Trimethylaluminum (TMAl) was used as the Al source, triethylgallium (TEGa) was used as the Ga source, and ammonia (NH ３ ) was used as the Si source. ４ ) was used.

[0110] Next, an n-type waveguide layer, which is a first waveguide layer, was formed on the first conductive type cladding layer. The n-type waveguide layer was an n-type AlGaN layer (Al: 63%, i.e., Al ０．６３ Ga ０．３７The n-type waveguide layer was formed to a thickness of 40 nm under the conditions of a temperature of 950°C, a reactor pressure of 300 mbar, and a V / III ratio of 4000. The growth rate of the n-type waveguide layer was 0.35 μm / hr. Trimethylaluminum (TMAl) was used as the Al source, triethylgallium (TEGa) was used as the Ga source, and ammonia (NH ３ ) was used.

[0111] Subsequently, a light-emitting layer was formed on the n-type waveguide layer. The light-emitting layer was formed to have a multi-quantum well structure in which quantum well layers and barrier layers were stacked in two cycles. Here, the quantum well layer was an AlGaN layer (Al: 52%, i.e., Al) with a thickness of 4.5 nm. ０．５２ Ga ０．４８ The barrier layer having a thickness of 6.0 nm was an AlGaN layer (Al: 63%, i.e., Al ０．６３ Ga ０．３７ The light-emitting layer was formed at a temperature of 950°C, 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 / hr, and the growth rate of the barrier layer was 0.15 μm / hr.

[0112] Next, a p-type waveguide layer, which is a second waveguide layer, was formed on the light-emitting layer. The p-type waveguide layer was an AlGaN layer containing no dopant (Al: 63%, i.e., Al ０．６３ Ga ０．３７ The p-type waveguide layer was formed to a thickness of 70 nm under the conditions of a temperature of 950°C, a reactor pressure of 300 mbar, and a V / III ratio of 4000. The growth rate of the p-type waveguide layer was 0.35 μm / hr. Trimethylaluminum (TMAl) was used as the Al source, and triethylgallium (TEGa) was used as the Ga source.

[0113] Subsequently, a second conductivity type cladding layer was formed on the p-type waveguide layer. The second conductivity type cladding layer was a compositionally graded layer with a graded Al composition. The second conductivity type cladding layer consisted of an AlGaN layer (interface graded portion) with a thickness of 2.5 nm, in which the Al composition was distributed in the direction away from the substrate, varying from Al=0.63 to 1.0, and a p-type AlGaN layer with a thickness of 330 nm, in which the Al composition was distributed in the direction away from the substrate, varying from Al=1.0 to 0.7. Before growing the second conductivity type cladding layer, the flow of metalorganic gas was temporarily stopped, and hydrogen and NH ３ The reactor pressure was set to 50 mbar with only irradiated laser light at a temperature of 950°C. Layer (A) (a layer formed of a sloped interface portion and a portion of a second-conductivity-type cladding layer) with an initial layer thickness of 72.5 nm and an Al composition corresponding to 0.63 → 1.0 → 0.95 was formed under conditions of a V / III ratio of 4000. The growth rate was 0.3 to 0.5 μm / hr. Here, layer (A) is a layer formed of a sloped interface portion and a portion of a second-conductivity-type cladding layer. Of the 72.5-nm-thick layer (A), a 2.5-nm-thick region where the Al composition changed from 0.63 to 1.0 is the "sloped interface portion," and the remaining 70-nm-thick region where the Al composition changed from 1.0 to 0.95 is the "portion of the second-conductivity-type cladding layer." The "sloped interface portion" is also a region included in the second-conductivity-type cladding layer.

[0114] Next, the flow of metalorganic gases was temporarily stopped, and hydrogen and NH ３ The reactor pressure was set to 50 mbar at a temperature of 1050°C while only irradiating the layer with Cr. The remaining layer (B) (a remaining part of the second conductivity type cladding layer) with a thickness of 257.5 nm and an Al composition equivalent to 0.98 → 0.7 was formed under conditions of a V / III ratio of 4000. The growth rate was 0.3 to 0.5 μm / hr. Trimethyl aluminum (TMAl) was used as the Al source throughout the growth. Triethyl gallium (TEGa) was used as the Ga source. The interface between the above-mentioned layers (A) and (B) corresponds to the region P where the impurity concentration profile changes abruptly or the composition discontinuous region Q where the Al composition is discontinuous in the direction away from the substrate.

[0115] Next, a p-type contact layer, which is a second conductivity type contact layer, was formed on the second conductivity type cladding layer. Here, the p-type contact layer was formed from an AlGaN layer and a GaN layer. The AlGaN layer was a 30 nm thick p-type nitride semiconductor layer using Mg as a dopant impurity and having an Al composition distribution that varied from Al = 0.7 to 0.4 in the direction away from the substrate. The GaN layer was formed from GaN (i.e., Al: 0%) with a thickness of 10 nm. The second conductivity type contact layer was formed at a temperature of 950°C, a reactor pressure of 150 mbar, and a V / III ratio of 3650. The growth rate of the second conductivity type contact layer was 0.2 μm / hr.

[0116] Various analyses were carried out on the nitride semiconductor laminate obtained as described above. As a result, the region where the Al composition was graded at the interface between the well layer and the barrier layer in the light-emitting layer was 0.5 nm. α, which indirectly represents potential fluctuation, was 146 meV. Next, a discontinuity in the Al composition was observed at the interface between the second conductivity type cladding layers (A) and (B), and the initial composition of (B) was 3% higher than that of (A). Furthermore, hydrogen was 5×10 １８ cm －３ , Si is 5 × 10 １８ cm －３ The FWHM of the hydrogen peak was 7.5 nm. Similarly, more oxygen and carbon were detected in (A) than in (B), and the concentration profile changed discontinuously at the interface between (A) and (B). The oxygen and carbon concentrations were 3×10 １７ cm －３ and 3 x 10 １７ cm －３ The second conductive type contact layer was SF ６ After removing the surface with gas, the surface was observed and found to have a spiral step-terrace structure based on a hexagonal shape, with a step height of 0.3 nm and a step density of 5 × 10 ７ cm －２ It was.

[0117] The semiconductor laminated portion formed as described above is ２The resistance of the second conductive type contact layer was further reduced by annealing it at 700° C. for 10 minutes or more in an atmosphere. ２ A mesa structure was formed by dry etching using a gas containing . The formed mesa structure had a length of 700 μm in the <1-100> direction and a length of 40 μm in the <11-20> direction. Here, the length of the mesa structure in the <1-100> direction is the distance between the cavity mirror end faces in a plan view, and the length in the <11-20> direction is the distance between the side faces of the mesa structure.

[0118] On the second conductivity-type contact layer of the mesa structure, Ni and Au films were sequentially deposited in a rectangular shape elongated in the <1-100> direction to form multiple electrode metal regions, which served as p-type second electrodes. The width of the second electrodes was 5 μm and the length was 600 μm or more. Furthermore, in the region where the n-type cladding layer of the mesa structure was exposed, V, Al, Ni, Ti, and Au films were sequentially deposited in a rectangular shape elongated in the <1-100> direction to form multiple electrode metal regions, which served as n-type first electrodes. The first and second electrodes were annealed at 550°C for 60 seconds in a nitrogen atmosphere using an RTA apparatus. Furthermore, the substrate was divided into stripes by cleaving the electrode metal regions multiple times parallel to the <11-20> direction, forming individual laser diodes. The length of the mesa structure in the <1-100> direction after division was 600 μm. The laser diode thus obtained was subjected to current injection and edge emission intensity measurement. The threshold voltage was 8 V and the oscillation threshold current was 3 kA / cm. ２ The oscillation time at this time was 100 seconds.

[0119] <Sample 2> to <Sample 4> Laser diodes of Samples 2 to 4 were fabricated in the same manner as Sample 1, except that the Al composition of the n-type AlGaN layer using Si as a dopant impurity that constitutes the first conductivity type cladding layer was changed as shown in Table 1.

[0120] <Sample 5> to <Sample 8> Laser diodes of Samples 5 to 8 were fabricated in the same manner as Sample 1, except that the thickness of the first conductivity type cladding layer was changed as shown in Table 1.

[0121] <Sample 9> to <Sample 25> Laser diodes of Samples 10 to 28 were formed in the same manner as Sample 1, except that the wafer temperature and reactor pressure during growth of the nitride semiconductor layers in forming the light-emitting layer, and the first and second conductivity type waveguide layers were changed as shown in Table 1. The growth temperature and growth pressure listed in the item for the light-emitting layer in Table 1 are the temperatures during formation of the light-emitting layer, and the first and second waveguide layers. α, which indirectly represents the potential fluctuation of the first waveguide layer at this time, took the values ​​shown in Table 1.

[0122] <Sample 26> to <Sample 29> Laser diodes Samples 26 to 29 were fabricated in the same manner as Sample 1, except that the wafer temperature during growth of the nitride semiconductor layer in the formation of the second conductivity-type cladding layer was changed as shown in Tables 1 and 2. The discontinuity at the discontinuous point in the Al composition and the concentration of carbon or oxygen contained in the second conductivity-type cladding layer were the values ​​shown in Table 1. Furthermore, observation of the surfaces of each sample revealed that Sample 26 had a spiral-shaped step-terrace with a circular base, Sample 27 had a circular step-terrace with some corners, Sample 28 had a spiral-shaped step-terrace structure with a base that was a mixture of hexagons and straight lines, and Sample 29 had a linear step-terrace structure.

[0123] <Sample 30> to <Sample 32> Laser diodes of Samples 30 to 32 were fabricated in the same manner as Sample 1, except that the reactor pressure during growth of the nitride semiconductor layer in forming a portion of the second conductivity type cladding layer on the substrate side was changed as shown in Table 2. The discontinuity at the discontinuous point in the Al composition and the concentration of carbon or oxygen contained in the second conductivity type cladding layer at this time were the values ​​shown in Table 2, respectively.

[0124] <Sample 33> to <Sample 35> Laser diodes of Samples 33 to 35 were fabricated in the same manner as Sample 1, except that the wafer temperature during growth of the nitride semiconductor layer when forming the remaining part of the second conductivity type cladding layer was changed as shown in Table 2. The discontinuity at the discontinuous point in the Al composition and the concentration of carbon or oxygen contained in the second conductivity type cladding layer at this time were the values ​​shown in Table 2, respectively.

[0125] <Sample 36> to <Sample 38> Laser diodes of Samples 36 to 38 were fabricated in the same manner as Sample 1, except that the reactor pressure during growth of the nitride semiconductor layer when forming the remaining part of the second conductivity type cladding layer was changed as shown in Table 2. The discontinuity at the discontinuous point in the Al composition and the concentration of carbon or oxygen contained in the second conductivity type cladding layer at this time were the values ​​shown in Table 2, respectively.

[0126] <Sample 39> to <Sample 42> Laser diodes 39 to 42 were fabricated in the same manner as Sample 1, except that the thickness of the remaining part of the second conductivity type cladding layer was changed to change the overall film thickness of the second conductivity type cladding layer as shown in Table 2. The discontinuity at the discontinuous point in the Al composition and the concentration of carbon or oxygen contained in the second conductivity type cladding layer at this time were the values ​​shown in Table 2, respectively.

[0127] <Sample 43> to <Sample 44> Laser diodes of Samples 43 and 44 were fabricated in the same manner as Sample 1, except that the thickness of the compositionally graded layer formed between the second conductivity type waveguide layer and the second conductivity type cladding layer was changed as shown in Table 2.

[0128] <Sample 45> to <Sample 49> Laser diodes 45 to 49 were fabricated in the same manner as Sample 1, except that the thickness of the region where the Al composition decreases in the portion of the second conductivity-type cladding layer on the substrate side was changed to 30 nm, 5 nm, 2 nm, 110 nm, and 150 nm, respectively, and the thickness of the remaining portion of the second conductivity-type cladding layer was changed so that the overall film thickness of the second conductivity-type cladding layer was 330 nm. Here, the thickness of the portion of the second conductivity-type cladding layer on the substrate side corresponds to the distance from the substrate side to the region where the Al composition becomes discontinuous or the carbon or oxygen concentration profile decreases discontinuously.

[0129] <Sample 50> to <Sample 53> Laser diodes of Samples 50 to 53 were formed in the same manner as Sample 1, except that the hydrogen concentration in a portion of the second conductivity type cladding layer on the substrate side was changed by changing the growth interruption time.

[0130] <Sample 54> to <Sample 55> Laser diodes of Samples 54 and 55 were formed in the same manner as Sample 1, except that the growth of the nitride semiconductor layer was not interrupted before or after forming a portion of the second conductivity type cladding layer on the substrate side.

[0131] <Sample 56> A laser diode of Sample 56 was formed in the same manner as Sample 1, except that a predetermined amount of Ga was continuously supplied during growth interruptions, and the second conductivity type cladding layer was formed so that there was no discontinuity in the Al composition at the interface between the portion of the second conductivity type cladding layer facing the substrate and the remaining portion.

[0132]

[0133]

[0134] Among Samples 1 to 56 in Tables 1 and 2, laser diodes having a second conductivity type cladding layer in which the growth of the nitride semiconductor layer was interrupted before and after forming a portion of the second conductivity type cladding layer on the substrate side, and in which the surface had a spiral step-terrace structure having terraces and steps other than linear in plan view, had lower overall threshold voltages and oscillation thresholds and longer oscillation times than laser diodes of Samples 27 and 29 which did not have such a spiral step-terrace structure. This confirmed that both suppression of cladding layer degradation and improvement of carrier injection efficiency were achieved.

[0135] Although the embodiments of the present disclosure have been described above, the above embodiments are merely examples of devices and methods for embodying the technical ideas of the present disclosure, and the technical ideas of the present disclosure do not specify the materials, shapes, structures, arrangements, etc. of the components. The technical ideas of the present disclosure can be modified in various ways within the technical scope defined by the claims.

[0136] REFERENCE SIGNS LIST 1, 2, 3 Laser diode 4 Light emitting element 10 Semiconductor laminate 11 Substrate 12 Buffer layer 13 First electrode 14 Second electrode 101 First conductivity type cladding layer 102 First conductivity type waveguide layer 103 Light emitting layer 104 Second conductivity type waveguide layer 105 Second conductivity type cladding layer 106 Contact layer

Claims

1. A method for manufacturing a nitride semiconductor laminate, comprising: forming a first conductivity type cladding layer containing a first conductivity type nitride semiconductor on a nitride semiconductor substrate containing Al; forming a light emitting layer on the first conductivity type cladding layer using a nitride semiconductor containing one or more quantum wells; forming a part of a second conductivity type cladding layer containing a second conductivity type nitride semiconductor under conditions of a wafer temperature of 900°C to 1000°C and a reactor pressure of 15 mbar to 350 mbar; and forming a remaining part of the second conductivity type cladding layer under conditions of a wafer temperature of 1030°C to 1100°C and a reactor pressure of 15 mbar to 350 mbar, thereby forming a semiconductor laminate portion on the nitride semiconductor substrate.

2. The method for producing a nitride semiconductor laminate according to claim 1, wherein the reactor pressure during formation of a portion of the second conductivity type cladding layer is 15 mbar or more and 100 mbar or less.

3. A method for manufacturing a nitride semiconductor stack as claimed in claim 1 or 2, comprising: flowing an organic metal gas during the formation of the first conductivity type cladding layer, the light emitting layer and the second conductivity type cladding layer; temporarily stopping the flow of the organic metal gas after the light emitting layer is formed and before forming a part of the second conductivity type cladding layer; and temporarily stopping the flow of the organic metal gas after forming a part of the second conductivity type cladding layer and before forming the remaining part of the second conductivity type cladding layer.

4. A method for manufacturing a nitride semiconductor device, comprising the steps of: forming the semiconductor laminate by the method for manufacturing a nitride semiconductor laminate according to any one of claims 1 to 3; removing unnecessary portions of each layer of the semiconductor laminate by etching; forming electrodes on the semiconductor laminate; and dividing the nitride semiconductor substrate on which the horn layer of the semiconductor laminate has been formed by dicing into individual pieces.

5. A nitride semiconductor device comprising: a nitride semiconductor substrate containing Al; and a semiconductor laminate portion disposed on the nitride semiconductor substrate, the semiconductor laminate portion having: a first conductivity type cladding layer containing a nitride semiconductor of a first conductivity type; a light emitting layer disposed on the first conductivity type cladding layer and formed of a nitride semiconductor including one or more quantum wells; and a second conductivity type cladding layer disposed on the light emitting layer and formed of a nitride semiconductor containing Al of a second conductivity type, the surface of the second conductivity type cladding layer having a spiral step-terrace structure having terraces and steps other than linear in plan view.

6. The nitride semiconductor device according to claim 5, wherein the height of the spiral step-terrace structure is not less than 0.2 nm and not more than 0.4 nm.

7. The distribution density of the spiral step-terrace structure is 1×10 ７ cm －２ Above 5 x 10 ８ cm －２ The nitride semiconductor device according to claim 5, wherein:

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

9. The first conductive type clad layer is Al ａ G （１－ａ） 6. The nitride semiconductor device according to claim 5, wherein the nitride semiconductor device is made of N (0.65<a≦0.9).

10. The nitride semiconductor device according to claim 5, wherein the first conductivity type cladding layer has a thickness of 250 nm or more and 800 nm or less.

11. The nitride semiconductor device according to claim 5, comprising: a first conductivity type waveguide layer disposed between the first conductivity type cladding layer and the light emitting layer, for confining light to the light emitting layer; and a second conductivity type waveguide layer disposed between the second conductivity type cladding layer and the light emitting layer, for confining light to the light emitting layer.

12. A second conductive type contact layer is disposed on the second conductive type cladding layer and is formed of a nitride semiconductor containing GaN, and the second conductive type cladding layer is Al ｄ G （１－ｄ） 6. The nitride semiconductor device according to claim 5, which contains N (0.1≦d≦1), has a composition gradient in which the Al composition d decreases with increasing distance from the nitride semiconductor substrate, and has a film thickness of 500 nm or less.

13. The nitride semiconductor device according to claim 12, wherein the second conductivity type cladding layer has a composition gradient in which the Al composition d decreases in the range of 1 to 0.7 with increasing distance from the nitride semiconductor substrate side.

14. The nitride semiconductor device according to claim 12 or 9, wherein the second conductive type cladding layer has a thickness of 250 nm or more and 400 nm or less.

15. The nitride semiconductor device according to claim 5, wherein a thickness T0 of the first conductivity type cladding layer is not less than 3300×a-2100 nm and not more than 15700×a-10100 nm (a is the proportion of Al atoms when the total number of Group III atoms in the nitride semiconductor constituting the first conductivity type cladding layer is taken as 1).

16. The resistivity of the first conductive type cladding layer is 1×10 －３ Ωcm or more 5×10 －３ The nitride semiconductor device according to claim 15, wherein the resistivity is Ωcm or less.

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