Laser diode

Abstract

To provide a laser diode with a low oscillation threshold current and threshold voltage.SOLUTION: A laser diode includes a nitride semiconductor substrate containing Al and a semiconductor stacked part 10 disposed on the nitride semiconductor substrate. The semiconductor laminated part includes: a nitride buffer layer containing Al disposed on a substrate; a first conductive type cladding layer 101 including a first conductive type nitride semiconductor layer; a light emitting layer 103 including one or more quantum wells and formed of a nitride semiconductor; a second conductivity type cladding layer 105 including a second conductive type nitride semiconductor layer; and a first waveguide layer 102 and a second waveguide layer 104 provided so as to sandwich the light emitting layer and confining light to the light emitting layer. Silicon is contained in at least one of an interface between the nitride semiconductor substrate and the nitride buffer layer, an interface between the nitride buffer layer and the first conductive type cladding layer, the first waveguide layer, the light emitting layer, the second wave path layer, and the second conductive type cladding layer in a range of 1×1015 cm-3 or more and is 1×1018 cm-3 or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Conventionally, nitride semiconductors have been used as materials for forming light-emitting diodes (LEDs) and laser diodes (LDs). 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). [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Zhang et al.,Applied Physics Express 12, 124003(2019) Summary of the Invention [Problem to be solved by the invention]

[0004] The ultraviolet laser diodes described above are pulse-driven, and continuous oscillation is required for practical applications, which requires reduction of the oscillation threshold current and threshold voltage. An object of the present disclosure is to provide a laser diode with a low oscillation threshold current and threshold voltage. [Means for solving the problem]

[0005] In order to solve the above-mentioned problems, a laser diode according to one embodiment of the present disclosure includes: a nitride semiconductor substrate containing Al; and a semiconductor laminate portion disposed on the nitride semiconductor substrate, wherein the semiconductor laminate portion includes: a nitride buffer layer disposed on the substrate and containing Al; a first-conductivity-type cladding layer disposed on the substrate and including a nitride semiconductor layer of the 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; a second-conductivity-type cladding layer disposed on the light-emitting layer and including a nitride semiconductor layer of a second conductivity type; a first waveguide layer disposed between the first-conductivity-type cladding layer and the light-emitting layer to confine light in the light-emitting layer; and a second waveguide layer disposed between the second-conductivity-type cladding layer and the light-emitting layer to confine light in the light-emitting layer. In the laser diode according to one embodiment of the present disclosure, silicon is present in an amount of 1×10 at least one of the interface between the nitride semiconductor substrate and the nitride buffer layer, the interface between the second waveguide layer and the second conductive type cladding layer, the first waveguide layer, the light emitting layer, the second waveguide layer, and the second conductive type cladding layer. 15 cm -3 More than 1×10 18 cm -3 The following is included: It should be noted that the above summary of the invention does not list all of the features of the present disclosure. [Effects of the Invention]

[0006] According to the present disclosure, it is possible to provide a laser diode with a low oscillation threshold current and a low threshold voltage. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a cross-sectional view schematically illustrating a configuration example of a laser diode according to an embodiment of the present disclosure. [Figure 2] 1 is a cross-sectional view schematically illustrating a configuration example of a laser diode according to an embodiment of the present disclosure. [Figure 3] 1 is a cross-sectional view schematically illustrating a configuration example of a laser diode according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0008] The laser diode according to the present disclosure will be described below through embodiments, but the following embodiments do not limit the scope of the invention according to the claims. Also, not all of the combinations of features described in the embodiments are necessarily essential to the solution of the invention. In the following description, the positive direction of the Z axis may be referred to as "up" and the negative direction of the Z axis may be referred to as "down." "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 idea of ​​the present disclosure. For example, if the paper is rotated 180 degrees, "up" will of course become "down" and "down" will become "up."

[0009] 1. Embodiment A laser diode according to an embodiment of the present disclosure will be described.

[0010] (1.1) Laser diode structure 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 nitride buffer layer disposed on the nitride semiconductor substrate and containing Al, a first-conductivity-type cladding layer disposed on the nitride semiconductor substrate and including a first-conductivity-type nitride semiconductor layer, a light-emitting layer disposed on the first-conductivity-type cladding layer and formed of a nitride semiconductor including one or more quantum wells, a second-conductivity-type cladding layer disposed on the light-emitting layer and including a second-conductivity-type nitride semiconductor layer, a first 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 waveguide layer disposed between the second-conductivity-type cladding layer and the light-emitting layer to confine light to the light-emitting layer. In the laser diode according to this embodiment, silicon is contained in an amount of 1×10 at least at an interface between the nitride semiconductor substrate and the nitride buffer layer, an interface between the second waveguide layer and the second-conductivity-type cladding layer, the first waveguide layer, the light-emitting layer, the second waveguide layer, and the second-conductivity-type cladding layer. 15 cm -3 More than 1×10 18 cm -3Includes the following: Each layer of the laser diode will now be described in detail.

[0011] <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 More than 1×10 4 cm -2 More preferably, it is:

[0012] Here, the "comprises" in the expression "comprises a nitride semiconductor" means that the layer mainly contains a nitride semiconductor, but this expression also includes cases where other elements are included. Specifically, this expression also includes cases where the composition of this layer is slightly modified by adding a small amount of an element other than the nitride semiconductor (for example, a few percent or less of an element such as Ga (when Ga is not the main element), In, As, P, or Sb). The wording "comprises" has a similar meaning when describing the composition of other layers. Furthermore, the small amount of elements contained is not limited to the above.

[0013] The substrate preferably has a thickness of 100 μm or more and 600 μm or less. The surface 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 surface 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.

[0014] <Nitride buffer layer> The nitride buffer layer (hereinafter sometimes referred to as the buffer layer) is formed between the substrate and the first conductivity type cladding layer, and is preferably formed over the entire surface of the substrate. By providing the buffer layer, a nitride semiconductor layer having 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.

[0015] 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 greater than 10 nm, the crystallinity of the nitride semiconductor such as AlN is enhanced. Furthermore, when the buffer layer is less than 10 μm thick, cracks are less likely to occur in the buffer layer formed by crystal growth over the entire wafer surface.

[0016] The interface between the buffer layer and the substrate is filled with silicon at a density of 1×10 15 cm -3 More than 1×10 18 cm -3 It is preferable that the following be contained: This allows stress to be concentrated at the interface, thereby increasing the luminous intensity of the light-emitting layer. In this embodiment, the "interface between the buffer layer and the substrate" refers to a region of 20 nm or less from the interface between the buffer layer and the substrate on both the buffer layer and the substrate side. In other words, it is sufficient that a predetermined amount of silicon is contained in a region of 20 nm or less above and below the interface between the buffer layer and the substrate.

[0017] <First-conductivity-type clad layer> The first-conductivity-type clad layer is formed on a substrate. Here, for example, in the expression "The first-conductivity-type clad layer is formed on a substrate", the word "on" means that the first-conductivity-type clad layer is formed on one surface of the substrate. Also, when there is another layer further between the substrate and the first-conductivity-type clad layer, it is included in the above expression. In the relationship between other layers, the word "above" has the same meaning. For example, when the second-conductivity-type clad layer is formed on the first waveguide layer via an electron blocking layer as described later, it is also included in the expression "The second-conductivity-type clad layer is formed on the first waveguide layer". In the description of this embodiment, "first-conductivity-type" and "second-conductivity-type" each mean a semiconductor indicating a different conductivity type. For example, when one is n-type conductivity, the other is p-type conductivity.

[0018] The first-conductivity-type clad layer is a layer of a nitride semiconductor containing Al and Ga. The first-conductivity-type clad layer is, for example, Al a Ga (1-a) N (0 < a < 1). Thereby, when forming a material corresponding to the bandgap energy in the deep ultraviolet region as a light-emitting layer, it becomes possible to enhance the crystallinity of the light-emitting layer and improve the light-emitting efficiency. From the viewpoint of realizing high light-emitting efficiency, the nitride semiconductor constituting the first-conductivity-type clad layer is preferably a mixed crystal of AlN and GaN. Also, from the viewpoint of growing the first-conductivity-type clad layer and each layer formed on the upper layer with perfect strain with respect to the substrate, the first-conductivity-type clad layer is Al a Ga (1-a) N (0.65 < a ≤ 0.9) is more preferably formed. The first-conductivity-type clad layer may be a gradient layer in which the Al composition increases as it moves away from the substrate for the purpose of controlling the longitudinal conductivity. In this case, the above limitation on the Al composition can be the Al composition averaged by the film thickness of the first-conductivity-type clad layer for the Al composition at the position in the film thickness direction within the first-conductivity-type clad layer.

[0019] 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 500 nm or less, and more preferably has a layer thickness of 300 nm or more and 450 nm or less.

[0020] The interface between the buffer layer and the first conductive type cladding layer is filled with silicon at a density of 1×10 15 cm -3 More than 1×10 18 cm -3 It is preferable that the following be contained: This allows stress to be concentrated at the interface, thereby increasing the luminous intensity of the light-emitting layer. The first conductive type clad layer contains 1×10 silicon. 18 cm -3 This does not apply when the n-type conductivity is obtained by doping the substrate with 1×10 or more. 15 cm -3 More than 1×10 18 cm -3 It is preferred to include the following: In this embodiment, the "interface between the buffer layer and the first-conductivity-type cladding layer" refers to a region of 20 nm or less from the interface between the buffer layer and the first-conductivity-type cladding layer on both the first-conductivity-type cladding layer and the buffer layer side. In other words, it is sufficient that a predetermined amount of silicon is contained in a region of 20 nm or less above and below the interface between the first-conductivity-type cladding layer and the buffer layer. Similarly, in this embodiment, when no buffer layer is used, the "interface between the substrate and the first-conductivity-type cladding layer" refers to a region of the substrate and the first-conductivity-type cladding layer that is 20 nm or less from the interface between the substrate and the first-conductivity-type cladding layer. In other words, it is sufficient that a predetermined amount of silicon is contained in a region that is 20 nm or less above and below the interface between the substrate and the first-conductivity-type cladding layer.

[0021] When the first conductive type clad layer is an n-type conductive semiconductor layer, it may contain impurities such as group V elements other than N such as P, As, Sb, and impurities such as C, H, F, O, Mg, Si, etc., but the types of impurity elements are not limited to this. From the viewpoints of reducing electrical resistance and the ease of obtaining raw materials, the impurity contained in the first conductive type clad layer is preferably Si, and the impurity concentration is 5×10 18 cm -3 or more and 5×10 19 cm -3 or less.

[0022] <Light-emitting layer> The light-emitting layer is a layer of a nitride semiconductor containing Al and Ga. The nitride semiconductor contained in the light-emitting layer is preferably, for example, a mixed crystal of AlN and GaN from the viewpoint of realizing high luminous efficiency. For example, Al b Ga (1-b) N (0 < b < 1). From the viewpoint of enhancing the luminous efficiency by suppressing point defects, it is preferable that Si is contained in the light-emitting layer, and it is more preferably contained at 1×10 15 cm -3 or more and 1×10 18 cm -3 or less, and it is even more preferably contained at 1×10 16 cm -3 or more and 1×10 17 cm -3 or less.

[0023] Also, the light-emitting layer can have either a multiple quantum well structure or a single quantum well structure. Although it depends on the longitudinal conductivity of the first conductive type clad layer and the second conductive type clad layer, the number of quantum well structures is preferably any one from 1 to 5.

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

[0025] From the perspective of optical confinement, the waveguide layer is preferably a nitride semiconductor containing Al and Ga having a bandgap higher in energy than the light-emitting layer. The waveguide layer preferably has an Al composition and a film thickness that increase the overlap between the electric field intensity distribution of the light standing in the device and the light-emitting layer. From the perspective of carrier confinement to the light-emitting layer, the light-emitting layer is made of Al b Ga (1-b) N (0 < b < 1), and when the waveguide layer is made of Al c Ga (1-c) N (0 < c < 1), it is more preferable that b < c and c ≧ b + 0.05. For example, when taking a light-emitting layer with an emission wavelength of 265 nm as an example, b is 0.52, and c is preferably 0.57 or more. Also, from the perspectives of optical confinement and sheet resistance, the total film thickness of the waveguide layer (the total film thickness of the film thickness of the first waveguide layer and the film thickness of the second waveguide layer) is preferably 70 nm or more and 150 nm or less.

[0026] From the perspective of improving carrier injection efficiency, it is preferable that Si is included in the waveguide layer, and it is more preferably included at 1×10 15 cm -3 or more and 1×10 18 cm -3 or less, and it is even more preferably included at 1×10 16 cm -3 or more and 1×10 17 cm -3It is more preferable that it is included below.

[0027] Each of the Al compositions of the first waveguide layer and the second waveguide layer is preferably uniform in the film thickness direction, but this is not the case. In order to avoid light absorption into a metal (for example, the second electrode) existing above the second conductive type clad layer described later, the Al composition of the second waveguide layer may be higher than the Al composition of the first waveguide layer. For the same purpose, the film thickness of the second waveguide layer may be thicker than the film thickness of the first waveguide.

[0028] <Second conductive type clad layer> The second conductive type clad layer is a nitride semiconductor layer containing Al and Ga having conductivity of the second conductive type, formed on the light emitting layer. The second conductive type clad layer is, for example, Al d Ga (1-d) formed by N (0 < d < 1). When a waveguide layer (second waveguide layer) is provided on the light emitting layer, the second conductive type clad layer is formed on the waveguide layer (second waveguide layer). Thereby, the second conductive type clad layer can easily achieve lattice matching with the light emitting layer or the waveguide layer, and can suppress the threading dislocation density.

[0029] The second conductive type clad layer has conductivity sufficient to inject carriers (electrons or holes) into the light emitting layer, and as long as it can increase the overlap between the electric field strength distribution of the standing light mode in the device and the light emitting layer (that is, increase the light confinement), the conductive type is not particularly limited. The second conductive type clad layer may be, for example, p-type AlGaN doped with Mg.

[0030] From the viewpoint of injecting carriers into the light emitting layer more efficiently, the second conductive type clad layer has an Al composition e that decreases as it moves away from the substrate, that is, an Al e Ga (1-e) composition gradient layer (second conductive type vertical conduction layer) formed by N (0.1 ≦ e ≦ 1) that slopes so as to decrease in the direction away from the upper surface of the substrate, and Al f Ga (1-f)It is preferable to include a second-conductivity-type lateral conduction layer containing N (0 < f ≤ 1).

[0031] From the viewpoint of enhancing the carrier injection efficiency, it is preferable that the second-conductivity-type cladding layer contains Si, and it is more preferably contained at 1×10 15 cm -3 or more and 1×10 18 cm -3 or less. Even more preferably, it is contained at 1×10 16 cm -3 or more and 1×10 17 cm -3 or less. Thereby, point defects are compensated, and the carrier injection efficiency into the second-conductivity-type cladding layer is enhanced, improving the light emission efficiency of the laser diode. From the viewpoint of the resistance of the entire second-conductivity-type cladding layer, it is preferable that Si is contained at the interface between the second-conductivity-type cladding layer and the second waveguide layer. Similarly, it is preferable that Si is contained in a part of the second-conductivity-type cladding layer. Similarly, it is preferable that Si is contained only in a region of 50 nm or less on the second-conductivity-type cladding layer side from the interface between the second-conductivity-type cladding layer and the second waveguide layer. In addition, when Si is contained in a region deeper (a region exceeding 50 nm) than the region of 50 nm or less on the second-conductivity-type cladding layer side from the interface between the second-conductivity-type cladding layer and the second waveguide layer, point defects in the second-conductivity-type cladding layer are compensated by Si. When Si is contained throughout the entire region of the second-conductivity-type cladding layer, the effect of improving the quality of the second-conductivity-type cladding layer due to the compensation of point defects in the entire second-conductivity-type cladding layer becomes greater than the improvement in the resistance of the entire second-conductivity-type cladding layer by Si, and there may be a case where the characteristics of the entire device are improved (for example, a decrease in the emission threshold). Hereinafter, the second-conductivity-type vertical conduction layer and the second-conductivity-type lateral conduction layer will be described.

[0032] (Second-Conductivity-Type Vertical Conduction Layer) The second-conductivity-type vertical conduction layer is a layer that constitutes the region on the light-emitting layer side of the second-conductivity-type cladding layer. The second-conductivity-type vertical conduction layer is Al e Ga<00,00073>It is a layer containing N (0.1 ≦ e ≦ 1). The profile (gradient) of the Al composition e in the second-conductive-type vertical conductive layer may continuously decrease or may intermittently decrease. Here, "intermittently decreasing" means including a portion where the Al composition e is the same (constant in the film thickness direction) in a part of the film of the second-conductive-type vertical conductive layer. That is, the second-conductive-type vertical conductive layer may include a portion where the Al composition e does not decrease in the direction away from the substrate, but does not include an increasing portion.

[0033] From the viewpoint of lattice matching, the film thickness of the second-conductive-type vertical conductive layer is preferably 500 nm or less. Further, from the viewpoint of lattice matching, it is more preferably 20 nm or more and 400 nm or less, and even more preferably 30 nm or more and 350 nm or less.

[0034] (Second-conductive-type lateral conductive layer) The second-conductive-type lateral conductive layer is a layer that constitutes a region on the opposite side of the light-emitting layer in the second-conductive-type cladding layer and is formed on the second-conductive-type vertical conductive layer. The second-conductive-type lateral conductive layer is Al f Ga (1-f) It is a layer containing N (0 < f ≦ 1). Here, the Al composition f on the surface of the second-conductive-type lateral conductive layer facing the second-conductive-type vertical conductive layer is preferably greater than the minimum value of the Al composition e of the second-conductive-type vertical conductive layer.

[0035] From the viewpoint of facilitating the quantum transmission of carriers passing through the second-conductive-type lateral conductive layer, the film thickness of the second-conductive-type lateral conductive layer is preferably 20 nm or less, more preferably 10 nm or less, and even more preferably 5 nm or less.

[0036] When a second-conductivity-type contact layer (described later) is provided on the second-conductivity-type lateral conduction layer, the Al composition at the interface between the second-conductivity-type lateral conduction layer and the second-conductivity-type contact layer is preferably smaller than the Al composition in the second-conductivity-type contact layer and is completely strained with respect to the substrate. Such a second-conductivity-type lateral conduction layer can improve lateral conductivity by induced carriers at the interface due to a negative net internal electric field accumulated at the surface and inside near the surface of the second-conductivity-type lateral conduction layer.

[0037] In this way, the second conductivity type vertical conduction layer generates carriers (for example, holes when the second conductivity type vertical conduction layer is formed of a p-type semiconductor) by the polarization doping effect, and has the effect of efficiently injecting the carriers into the active layer in the light emitting layer. Therefore, by providing the second conductivity type vertical conduction layer on the light emitting layer, the carrier injection efficiency of the laser diode can be increased and the threshold voltage can be reduced.

[0038] In addition, the second-conductivity-type lateral conduction layer has the effect of spreading the carrier distribution, which is narrowed by the electric field concentrated under the electrode, in the lateral direction (within the plane of the second-conductivity-type lateral conduction layer). Due to this effect, the second-conductivity-type lateral conduction layer can increase the carrier injection efficiency into the light-emitting layer, just like the second-conductivity-type vertical conduction layer.

[0039] <Second-conductivity-type contact layer> The semiconductor laminate of the laser diode of this embodiment may further include a second-conductivity-type contact layer disposed on the second-conductivity-type cladding layer. The nitride semiconductor constituting the second-conductivity-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.

[0040] 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 x 10 or less. 20 cm -3 5x10 or more 21 cm -3 More preferably, it is:

[0041] The thickness of the second conductive type contact layer is preferably 1 nm or more and 20 nm or less. The thinner the second conductive type contact layer, the higher the carrier injection efficiency of the light emitting layer, and the thicker the layer, the lower the carrier injection efficiency.

[0042] <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 bandgap larger than that of the light emitting layer. The electron blocking layer may be provided, for example, on the light emitting layer, inside the second waveguide layer, between the second waveguide layer and the light emitting layer, or between the second waveguide layer and the second conductivity type vertical conductive layer. The thickness of the electron blocking layer is preferably 30 nm or less, and more preferably 20 nm or less, so that carriers (holes) can easily quantum-transport through the electron blocking layer.

[0043] <Electrode> 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, where 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.

[0044] 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.

[0045] When the first conductivity type cladding layer is an n-type cladding layer, the first electrode is formed 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, a mixed crystal of these metals, or a conductive oxide such as ITO or Ga2O3. When the first conductivity type cladding layer is a p-type cladding layer, the first electrode is formed 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, or Zr, a mixed crystal of these metals, or a conductive oxide such as ITO or Ga2O3.

[0046] When the second conductivity type cladding layer is an n-type cladding layer, the second electrode is formed 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, a mixed crystal of these metals, or a conductive oxide such as ITO or Ga2O3. When the second conductivity type cladding layer is a p-type cladding layer, the second electrode is formed from a metal such as Ni, Au, Pt, Ag, Rh, Pd, Pt, Cu, Al, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Co, Ir, or Zr, a mixed crystal of these metals, or a conductive oxide such as ITO or Ga2O3.

[0047] The placement area and shape of the first electrode and the second electrode are not limited as long as they are in electrical contact 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).

[0048] The laser diode described above has a specific layer (interface) of 1×10 15 cm -3 More than 1×10 18 cm -3 It is sufficient that the following silicon is contained, and in this case, impurities other than silicon may be contained in the buffer layer, first waveguide layer, light emitting layer, second waveguide layer, etc. For example, impurities such as P, As, Sb, and other V group elements other than N, C, H, F, O, and Mg may be mixed into each layer, but the types of impurity elements are not limited to these.

[0049] (1.2) Manufacturing method of ultraviolet laser diode The laser diode of this embodiment is manufactured through a process of forming each layer on a substrate. (Formation of substrate) The substrate is dye sublimation, The layer is formed by a general substrate growth method such as a vapor phase growth method, such as hydride vapor phase epitaxy (HVPE), or a liquid phase growth method.

[0050] (Formation of semiconductor laminate) Each layer of the semiconductor laminate formed on the substrate can be formed by, for example, molecular beam epitaxy (MBE), hydride vapor phase epitaxy (HVPE), or metal organic chemical vapor deposition (MOCVD). Here, among the layers formed on the substrate, the nitride semiconductor layer can be formed using, for example, an Al raw material containing trimethylaluminum (TMAl), a Ga raw material containing trimethylgallium (TMGa) or triethylgallium (TEGa), or an N raw material containing ammonia (NH3).

[0051] The semiconductor laminate section forms a first conductivity type cladding layer containing a first conductivity type nitride semiconductor on a buffer layer formed on a substrate, then forms a light emitting layer on the first conductivity type cladding layer using a nitride semiconductor (such as AlGaN) containing one or more quantum wells, and then forms a second conductivity type cladding layer on the light emitting layer. If necessary, waveguide layers (first and second waveguide layers) made of a nitride semiconductor such as AlGaN may be formed above and below the light-emitting layer. In addition, an intermediate layer made of a nitride semiconductor such as AlGaN may be formed between the second-conductivity-type cladding layer and the second waveguide layer, a second-conductivity-type contact layer made of a nitride semiconductor containing GaN may be provided on the second-conductivity-type cladding layer, or an electron blocking layer may be formed above the light-emitting layer.

[0052] Laser diodes are manufactured through a process of 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, for example, by inductively coupled plasma (ICP) etching. In the mesa structure forming step, unnecessary portions of each layer of the conductor laminated portion are removed by etching, thereby exposing a part of the first conductivity type cladding layer.

[0053] (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 deposited 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. After the layers are formed, each electrode can be heat-treated in an oxygen, nitrogen, or air atmosphere. Finally, the substrate on which the layers have been formed through the above-described steps is divided into individual pieces by dicing, thereby manufacturing the laser diodes.

[0054] 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 nitride semiconductor layer. The alloying method is not particularly limited as long as sufficient contact with the nitride semiconductor layer can be obtained. As described above, according to the method for manufacturing a laser diode according to this embodiment, it is possible to improve the carrier injection efficiency and increase the emission intensity.

[0055] 2.Measuring methods for the physical properties of laser diodes The physical properties of the laser diode described above can be measured as follows.

[0056] (Layer thickness measurement method) The thickness of each layer constituting a laser diode can be measured by cutting 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 the 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 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.

[0057] (Measurement of impurity and doping concentrations) The concentration of dopants and impurities contained in each layer constituting the laser diode can be measured by secondary ion mass spectrometry (SIMS). When measuring the concentration of dopants and impurities in each layer by SIMS after processing into a device, the measurement can be performed after removing the electrodes by chemical etching or physical polishing. The concentration of dopants and impurities in each layer can also be measured by sputtering from the substrate side where no electrodes are formed. Specifically, SIMS measurements are performed under the measurement conditions provided by Evans Analytical Group (EAG), Inc. A cesium (Cs) ion beam with an energy of 14.5 keV is used to sputter the sample during the measurements.

[0058] (Method for measuring atomic concentration of each layer) One method for measuring the atomic concentration of each layer that constitutes a laser diode is reciprocal space mapping (RSM) using X-ray diffraction (XRD). Specifically, the lattice relaxation rate and Al composition relative to the substrate can be obtained by analyzing reciprocal lattice mapping data near the diffraction peak obtained using an asymmetric plane as the diffraction plane. Examples of diffraction planes include the (10-15) plane and the (20-24) plane.

[0059] Furthermore, layers and regions that do not provide sufficient reflection intensity by XRD, such as the light-emitting layer, 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).

[0060] EELS analyzes the composition of a sample by measuring the energy lost when an electron beam 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 observation. The position of the 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.

[0061] In the same manner as the layer thickness calculation method 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 area of ​​2 μm or more.

[0062] EDX measures and analyzes the characteristic X-rays generated by an electron beam in a thin-sectioned sample used in the above-mentioned TEM observation, etc. In the same way 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 area of ​​2 μm or more.

[0063] XPS allows for depth profile 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 depth profile of the Al composition in each layer can be obtained by measuring and analyzing the XPS peak intensities of Al, Ga, and N. Instead of sputter etching, the laser diode can be polished at an angle 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.

[0064] In addition to XPS, Auger Electron Spectroscopy (AES) can also be used to measure the composition of each layer. In this case, the composition can be measured by 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.

[0065] (Ultraviolet laser diode application fields) 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.

[0066] Examples of liquid sterilization equipment 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 equipment, garbage disposals, toilet drain traps, washing machines, dialysis water sterilization modules, peritoneal dialysis connector sterilizers, and disaster water storage systems.

[0067] Examples of gas sterilization devices 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, chests of drawers, etc. Examples of solid sterilization equipment (including surface sterilization equipment) include, but are not limited to, vacuum sealers, belt conveyors, hand tool sterilizers for medical, dental, barber, and beauty salon use, toothbrushes, toothbrush holders, chopstick cases, cosmetic pouches, drain covers, toilet spot cleaners, and toilet lids.

[0068] 3. Examples of laser diodes The laser diode of this embodiment will be described in more detail below with reference to Fig. 1. The detailed configuration of each layer in each of the following embodiments is as described above.

[0069] (3.1) First embodiment Fig. 1 is a cross-sectional view of a laser diode 1 according to a first embodiment. As shown in Fig. 1, the laser diode 1 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 waveguide layer 102, a light-emitting layer 103, a second waveguide layer 104, and a second conductivity-type cladding layer 105 having a p-type conductivity.

[0070] (3.2) Second embodiment Fig. 2 is a cross-sectional view of a laser diode 2 according to a second embodiment. As shown in Fig. 2, the laser diode 2 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 waveguide layer 102, a light-emitting layer 103, a second 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 the laser diode 2 does not include the buffer layer 12.

[0071] (3.3) Third embodiment Fig. 3 is a cross-sectional view of a laser diode 3 according to a third embodiment. As shown in Fig. 3, 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 waveguide layer 102, a light-emitting layer 103, a second 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 a contact layer 106 . The laser diode of the present disclosure may not include the buffer layer 12 as described in the second embodiment, and may include the contact layer 106 as described in the third embodiment.

[0072] 4.Effects The above-described laser diode has the following advantages.

[0073] (1) A semiconductor device comprising: a nitride semiconductor substrate containing Al; and a semiconductor laminate portion disposed on the nitride semiconductor substrate, the semiconductor laminate portion comprising: a nitride buffer layer disposed on the nitride semiconductor substrate and containing Al; a first-conductivity-type cladding layer disposed on the nitride semiconductor substrate and including a nitride semiconductor layer of a first conductivity type; a light-emitting layer disposed on the first-conductivity-type cladding layer and formed of a nitride semiconductor including one or more quantum wells; a second-conductivity-type cladding layer disposed on the light-emitting layer and including a nitride semiconductor layer of a second conductivity type; a first waveguide layer disposed between the first-conductivity-type cladding layer and the light-emitting layer to confine light in the light-emitting layer; and a second waveguide layer disposed between the second-conductivity-type cladding layer and the light-emitting layer to confine light in the light-emitting layer, and wherein silicon is present in an amount of 1×10 at least in one of an interface between the nitride semiconductor substrate and the nitride buffer layer, an interface between the second waveguide layer and the second-conductivity-type cladding layer, the first waveguide layer, the light-emitting layer, the second waveguide layer, and the second-conductivity-type cladding layer. 15 cm -3 More than 1×10 18 cm -3 The following is included: This makes it possible to increase the light emission efficiency of the laser diode, improve the oscillation threshold current density, and reduce the threshold voltage of the laser diode.

[0074] (2) In the laser diode, the second conductive cladding layer is made of silicon at 5×10 15 cm -3 More than 1×10 17 cm -3 It is preferred to include the following: This compensates for point defects, and the efficiency of carrier injection is improved, making it possible to reduce the oscillation threshold current density.

[0075] (3) In the laser diode, it is preferable that silicon is contained at the interface between the second conductivity type cladding layer and the second waveguide layer. This makes it possible to increase the carrier injection efficiency while keeping the film resistance low.

[0076] (4) In the laser diode, it is preferable that at least the second conductivity type cladding layer contains silicon, and that only a portion of the second conductivity type cladding layer contains silicon. This makes it possible to increase the carrier injection efficiency while keeping the film resistance low.

[0077] (5) In the laser diode, the second conductivity type cladding layer preferably contains silicon only in a region extending from the interface between the second conductivity type cladding layer and the second waveguide layer toward the inside of the second conductivity type cladding layer by 50 nm or less. This makes it possible to increase the carrier injection efficiency while keeping the film resistance low.

[0078] (6) In the laser diode, silicon is present at an interface between the substrate and the nitride buffer layer and at an interface between the nitride buffer layer and the first conductivity type cladding layer, respectively. 15 cm -3 More than 1×10 18 cm -3 It is preferred that the following be included: This makes it possible to increase the light-emitting efficiency by concentrating stress on each interface.

[0079] (7) In a laser diode, the nitride buffer layer containing Al is preferably AlN. As a result, a nitride semiconductor layer with a small difference in lattice constant and thermal expansion coefficient and few defects is formed on the buffer layer, making it possible to increase the light-emitting efficiency.

[0080] (8) In a laser diode, the nitride semiconductor substrate is preferably an AlN single crystal substrate. This reduces the difference in lattice constant between the substrate and the nitride semiconductor layer formed on the upper side of the substrate, and by growing the nitride semiconductor layer in a lattice-matched system, threading dislocations can be reduced, and a highly stable nitride semiconductor layer can be formed.

[0081] (9) In a laser diode, the first conductive type clad layer is preferably formed of Al a Ga (1-a) N (0.65 < a ≤ 0.9). <00005​​​​​​​​​​​​​​​​​​Preferably, it has a second-conductivity-type lateral conduction layer including N (0 < f ≦ 1). Thereby, carriers can be injected into the light-emitting layer more efficiently, and an improvement in light-emitting efficiency can be obtained.

[0084] (12) In a laser diode, the Al composition f on the surface of the second-conductivity-type lateral conduction layer facing the second-conductivity-type vertical conduction layer is preferably greater than the minimum value of the Al composition e of the second-conductivity-type vertical conduction layer. Thereby, the lateral carrier spread becomes good, and the carrier injection efficiency can be increased. Thereby, it becomes possible to increase the light-emitting efficiency.

Example

[0085] Hereinafter, examples and comparative examples of the present disclosure will be described. Note that the laser diode of the present disclosure is not limited to these examples.

[0086] <Example 1> An (0001) plane AlN single crystal substrate with a thickness of 550 μm was used as the substrate. Next, monosilane (SiH4) was used as the Si raw material, and the raw material was supplied for 3 minutes. An AlN layer, which is a buffer layer, was formed on the substrate after the SiH4 supply. The AlN layer was formed with 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 raw material gas to the supply rate of the nitrogen raw material gas was 50. The growth rate of the AlN layer at this time was 0.5 μm / hr. Also, trimethylaluminum (TMAl) was used as the Al raw material. Also, ammonia (NH3) was used as the N raw material.

[0087] A first-conductivity-type cladding layer was formed on this substrate. Before forming the first-conductivity-type cladding layer, monosilane (SiH4) was used as the Si raw material, and the raw material was supplied for 3 minutes. The first-conductivity-type cladding layer is an n-type AlGaN layer (Al: 75%, that is, Al 0.75 Ga 0.25The first conductivity type cladding layer was formed to a thickness of 400 nm under the conditions of a temperature of 1080°C, a degree of vacuum of 50 mbar, and a V / III ratio of 4000. The growth rate of the first conductivity type cladding layer was 0.4 μm / hr. Trimethylaluminum (TMAl) was used as the Al source, triethylgallium (TEGa) was used as the Ga source, ammonia (NH3) was used as the N source, and monosilane (SiH4) was used as the Si source.

[0088] 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 AlGaN layer containing no dopants (Al: 63%, i.e., Al 0.63 Ga 0.37 The n-type waveguide layer was formed to a thickness of 60 nm under the conditions of a temperature of 1080°C, a degree of vacuum of 50 mbar, and a V / III ratio of 4000. The growth rate of the n-type waveguide layer was 0.35 μm / hr. Trimethylaluminum (TMAl) was used as the Al source, triethylgallium (TEGa) was used as the Ga source, and ammonia (NH3) was used as the N source.

[0089] Subsequently, a light-emitting layer was formed on the first waveguide layer. The light-emitting layer was formed to have a multi-quantum well structure in which quantum well layers and barrier layers were stacked three times. Here, the quantum well layer was an AlGaN layer (Al: 52%, i.e., Al) with a thickness of 3.0 nm. 0.52 Ga 0.48 The barrier layer having a thickness of 6.0 nm was an AlGaN layer (Al: 63%, i.e., Al 0.63 Ga 0.37 N layer). Note that neither the quantum well layer nor the barrier layer contained a dopant. The light-emitting layer was formed under conditions of a vacuum of 50 mbar and a V / III ratio of 4000. The growth rate of the quantum well layer was 0.18 μm / hr, and the growth rate of the barrier layer was 0.15 μm / hr.

[0090] 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 dopants (Al: 63%, i.e., Al 0.63 Ga 0.37 The p-type waveguide layer was formed to a thickness of 60 nm at a temperature of 1080°C, a vacuum of 50 mbar, and a V / III ratio of 4000. The growth rate of the p-type waveguide layer was 0.35 μm / hr. Trimethylaluminum (TMAl) was used as the Al source, and triethylgallium (TEGa) was used as the Ga source.

[0091] Next, a second-conductivity-type cladding layer was formed on the p-type waveguide layer. The second-conductivity-type cladding layer had a layered structure comprising a second-conductivity-type vertical conduction layer and a second-conductivity-type horizontal conduction layer, and was a graded layer with a gradient Al composition ratio. The second-conductivity-type vertical conduction layer was an AlGaN layer with a thickness of 325 nm, with an Al composition distribution ranging from Al = 1.0 to 0.7 in the direction away from the substrate. The second-conductivity-type vertical conduction layer was doped with Si using monosilane (SiH4) as the Si source. The second conductivity type cladding layer was formed at a temperature of 1080°C, under a vacuum of 50 mbar, with a V / III ratio of 4000. The growth rate of the second conductivity type cladding layer was 0.3 to 0.5 μm / hr. Trimethylaluminum (TMAl) was used as the Al source, and triethylgallium (TEGa) was used as the Ga source. The second conductivity type lateral conduction layer was an AlGaN layer with Al=0.8 and a layer thickness of 5 nm, resulting in a total thickness of the second conductivity type cladding layer of 330 nm.

[0092] Next, a p-type contact layer, which is a second conductivity type contact layer, was formed on the second conductivity type cladding layer. Here, the p-type contact layer was formed from an AlGaN layer and a GaN layer. The AlGaN layer was a p-type nitride semiconductor layer with a thickness of 30 nm, using Mg as a dopant impurity and with an Al composition distribution that varied from Al = 0.7 to 0.4 in the direction away from the substrate. The GaN layer was formed from GaN (i.e., Al: 0%) with a thickness of 10 nm. The second conductivity type contact layer was formed under the conditions of a temperature of 950°C, a degree of vacuum of 150 mbar, and a V / III ratio of 3650. The growth rate of the second conductivity type contact layer at this time was 0.2 μm / hr.

[0093] The nitride semiconductor laminate obtained as described above was subjected to SIMS measurement. As a result, it was found that 5×10 17 cm -3 In addition, 1×10 Si was detected in the second conductivity type clad layer. 16 cm -3 The Si content in the other layers was below the detection limit of 1 × 10 15 cm -3 below 1×10 15 cm -3 It was less than.

[0094] In this way, a semiconductor laminate was formed on an AlN substrate. When reciprocal lattice mapping measurement was performed on this semiconductor laminate by XRD, it was found that the semiconductor laminate had undergone pseudomorphic growth without relaxation up to the second conductivity-type contact layer.

[0095] The semiconductor laminate formed as described above was annealed in an N2 atmosphere at 700°C for 10 minutes or more to further reduce the resistance of the second conductivity type contact layer. Dry etching was performed using an ICP with a gas containing Cl2 to form a mesa structure that exposed the first conductivity type cladding layer.

[0096] 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.

[0097] On the second conductivity-type contact layer of the mesa structure, Ni and Au films were sequentially deposited in a rectangular shape extending in the <1-100> direction to form multiple electrode metal regions, which served as p-type second electrodes. The width of the second electrode was 5 μm, and its 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 extending 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 system.

[0098] Furthermore, the substrate was divided into stripes by cleaving multiple times parallel to the <11-20> direction within the electrode metal region, forming individual laser diodes. The length of the mesa structure in the <1-100> direction after division was 600 μm.

[0099] <Example 2> A laser diode of Example 2 was fabricated in the same manner as in Example 1, except that the light-emitting layer was doped with Si using monosilane (SiH4) as the Si source. SIMS measurement revealed that the light-emitting layer contained 1×10 16 cm -3 The Si content in the other layers was the same as in Example 1.

[0100] Example 3 The laser diode of Example 3 was fabricated in the same manner as in Example 1, except that the first waveguide layer was doped with Si using monosilane (SiH4) as the Si source. SIMS measurement revealed that the first waveguide layer contained 1×10 16 cm -3 The Si content in the other layers was the same as in Example 1.

[0101] Example 4 The laser diode of Example 4 was fabricated in the same manner as in Example 1, except that the second waveguide layer was doped with Si using monosilane (SiH4) as the Si source. As a result of SIMS measurement, it was found that the second waveguide layer contained 1×10 16 cm-3 The Si content in the other layers was the same as in Example 1.

[0102] <Example 5> The laser diode of Example 5 was fabricated in the same manner as in Example 1, except that the amount of Si doped at the interface between the substrate and the buffer layer was changed by changing the supply amount of monosilane (SiH4). SIMS measurement revealed that 1×10 16 cm -3 The Si content in the other layers was the same as in Example 1.

[0103] Example 6 The laser diode of Example 6 was fabricated in the same manner as in Example 1, except that the amount of Si doped at the interface between the substrate and the buffer layer was changed by changing the supply amount of monosilane (SiH4). SIMS measurement revealed that 1×10 18 cm -3 The Si content in the other layers was the same as in Example 1.

[0104] Example 7 The laser diode of Example 7 was fabricated in the same manner as in Example 1, except that the amount of Si doped at the interface between the substrate and the buffer layer was changed by changing the supply amount of monosilane (SiH4). SIMS measurement revealed that 5×10 18 cm -3 The Si content in the other layers was the same as in Example 1.

[0105] Example 8 The laser diode of Example 8 was fabricated in the same manner as in Example 1, except that the supply rate of monosilane (SiH4) was changed and Si doping was not performed at the interface between the substrate and the buffer layer. SIMS measurement revealed that the Si content at the interface between the substrate and the buffer layer was 1×10 15 cm -3 The Si content in the other layers was the same as in Example 1.

[0106] Example 9 The laser diode of Example 9 was fabricated in the same manner as in Example 1, except that the supply amount of monosilane (SiH4) was changed and Si doping was not performed when the second conductivity type cladding layer was formed. As a result of SIMS measurement, the Si content in the second conductivity type cladding layer was 1×10 15 cm -3 The Si content in the other layers was the same as in Example 1.

[0107] Example 10 A laser diode of Example 10 was fabricated in the same manner as in Example 1, except that the amount of Si doped in the second conductivity type cladding layer was changed by changing the supply amount of monosilane (SiH4). As a result of SIMS measurement, it was found that the amount of Si doped in the second conductivity type cladding layer was 5×10 15 cm -3 The Si content in the other layers was the same as in Example 1.

[0108] Example 11 A laser diode of Example 11 was fabricated in the same manner as in Example 1, except that the amount of Si doped in the second conductivity type cladding layer was changed by changing the supply amount of monosilane (SiH4). As a result of SIMS measurement, it was found that the amount of Si doped in the second conductivity type cladding layer was 1×10 17 cm -3 The Si content in the other layers was the same as in Example 1.

[0109] Example 12 A laser diode of Example 12 was fabricated in the same manner as in Example 1, except that the amount of Si doped in the second conductivity type cladding layer was changed by changing the supply amount of monosilane (SiH4). As a result of SIMS measurement, it was found that the amount of Si doped in the second conductivity type cladding layer was 5×10 17 cm -3 The Si content in the other layers was the same as in Example 1.

[0110] Example 13 A laser diode of Example 13 was fabricated in the same manner as in Example 1, except that the amount of Si doped in the second conductivity type cladding layer was changed by changing the supply amount of monosilane (SiH4). As a result of SIMS measurement, it was found that the amount of Si doped in the second conductivity type cladding layer was 1×10 18 cm -3 The Si content in the other layers was the same as in Example 1.

[0111] Example 14 A laser diode of Example 14 was fabricated in the same manner as in Example 1, except that the amount of Si doped in the second conductivity type cladding layer was changed by changing the supply amount of monosilane (SiH4). As a result of SIMS measurement, it was found that the amount of Si doped in the second conductivity type cladding layer was 5×10 18 cm -3 The Si content in the other layers was the same as in Example 1.

[0112] Example 15 A laser diode of Example 15 was fabricated in the same manner as in Example 1, except that when forming the second conductivity type vertical conductive layer, Si doping was performed up to a film thickness of 20 nm, and thereafter Si doping was not performed. As a result of SIMS measurement, it was found that Si was 1×10 in the region from the second waveguide layer of the second conductivity type cladding layer to a film thickness of 20 nm. 16 cm -3 The Si content in the other regions of the second conductivity type cladding layer was 1×10 15 cm -3 The Si content in the other layers was the same as in Example 1.

[0113] Example 16 A laser diode of Example 16 was fabricated in the same manner as in Example 1, except that when forming the second conductivity type vertical conductive layer, Si doping was performed up to a film thickness of 40 nm, and thereafter Si doping was not performed. As a result of SIMS measurement, it was found that Si was 1×10 in the region from the second waveguide layer of the second conductivity type cladding layer to a film thickness of 40 nm. 16 cm -3The Si content in the other regions of the second conductivity type cladding layer was 1×10 15 cm -3 The Si content in the other layers was the same as in Example 1.

[0114] Example 17 A laser diode of Example 17 was fabricated in the same manner as in Example 1, except that when forming the second conductivity type vertical conductive layer, Si doping was performed up to a film thickness of 70 nm, and thereafter Si doping was not performed. As a result of SIMS measurement, it was found that Si was 1×10 in the region from the second waveguide layer of the second conductivity type cladding layer to a film thickness of 70 nm. 16 cm -3 The Si content in the other regions of the second conductivity type cladding layer was 1×10 15 cm -3 The Si content in the other layers was the same as in Example 1.

[0115] <Comparative Example 1> A laser diode of Comparative Example 1 was fabricated in the same manner as in Example 1, except that monosilane (SiH4) was not supplied to the interface between the substrate and the buffer layer and the interface with the buffer layer, and Si was not doped into the second conductivity type cladding layer. SIMS measurement revealed that the Si content at the interface between the substrate and the buffer layer was 1×10 15 cm -3 The Si content in the second conductivity type cladding layer is less than 1×10 15 cm -3 It was less than.

[0116] [evaluation] For the laser diodes of each example and comparative example obtained as described above, current-facet emission intensity measurements were performed by current injection, and the threshold voltage and oscillation threshold current were measured. The evaluation results for each example and comparative example are shown in Table 1 below.

[0117] [Table 1]

[0118] As shown in Table 1, silicon is present in an amount of 1×10 at least at one of the interfaces between the nitride semiconductor substrate and the nitride buffer layer, the interface between the nitride buffer layer and the first conductive type cladding layer, the first waveguide layer, the light emitting layer, the second waveguide layer, and the second conductive type cladding layer. 15 cm -3 More than 1×10 18 cm -3 The threshold voltage and oscillation threshold current of the laser diode of each of the examples included below were all lower than the threshold voltage and oscillation threshold current of the laser diode of the comparative example. In addition, the second conductive type clad layer contains silicon at 5×10 15 cm -3 More than 1×10 17 cm -3 The laser diodes of Examples 1 and 10 to 13, including those described below, had further reduced threshold voltages and oscillation threshold currents compared to Examples 9 and 14, in which the second conductivity type cladding layer contained silicon outside the above-mentioned range.

[0119] Furthermore, the laser diodes of Examples 15 and 16, which contain silicon only in a portion of the second-conductivity-type cladding layer, particularly in a region of 50 nm or less from the interface between the second-conductivity-type cladding layer and the second waveguide layer toward the inside of the second-conductivity-type cladding layer, exhibited a further reduction in oscillation threshold compared to Example 1, which contains silicon throughout the second-conductivity-type cladding layer. This is thought to be because stress is concentrated at the interface due to the inclusion of silicon in a portion of the second-conductivity-type cladding layer (at the interface with the second waveguide layer). Furthermore, silicon is added at the interface between the substrate and the nitride buffer layer and at the interface between the nitride buffer layer and the first conductivity type cladding layer, respectively. 15 cm -3 More than 1×10 18 cm -3 The laser diodes of Examples 1 to 6 included below had a further reduced oscillation threshold compared to Example 7 or Example 8, which contained silicon at the interface in an amount outside the above-mentioned range. Therefore, it was found that the laser diodes of Examples 1 to 6 had improved light emission efficiency. Similarly, in the second conductive type cladding layer, silicon is 1×1015 cm -3 More than 1×10 18 cm -3 The laser diodes of Examples 1 and 10 to 13 included below had further reduced threshold voltages and oscillation thresholds compared to Examples 9 and 14, in which the second conductivity type cladding layer contained silicon in amounts outside the above-mentioned ranges. Therefore, it was found that the laser diodes of Examples 1 and 10 to 13 had improved light-emitting efficiency.

[0120] 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. [Explanation of symbols]

[0121] 1,2,3 Laser Diode 10 Semiconductor laminated section 11 Circuit Board 12 Buffer layer 13 1st electrode 14 2nd electrode 101 First conductive type cladding layer 102 First waveguide layer 103 Light-emitting layer 104 Second waveguide layer 105 Second conductive type cladding layer 106 Contact layer

Claims

1. a nitride semiconductor substrate containing Al; a semiconductor laminate portion disposed on the nitride semiconductor substrate; Equipped with The semiconductor laminate portion is a nitride buffer layer containing Al and disposed on the nitride semiconductor substrate; a first conductivity type cladding layer disposed on the nitride semiconductor substrate and including a first conductivity type nitride semiconductor layer; a light emitting layer formed of a nitride semiconductor including one or more quantum wells and disposed on the first conductivity type cladding layer; a second conductivity type cladding layer disposed on the light emitting layer and including a second conductivity type nitride semiconductor layer; a first waveguide layer disposed between the first conductivity type cladding layer and the light emitting layer to confine light to the light emitting layer; a second waveguide layer disposed between the second conductive type cladding layer and the light emitting layer to confine light to the light emitting layer; Silicon is present in an amount of 1×10 at least at one of the interface between the nitride semiconductor substrate and the nitride buffer layer, the interface between the second waveguide layer and the second conductive type clad layer, the first waveguide layer, the light emitting layer, the second waveguide layer, and the second conductive type clad layer. １５ cm －３ 1x10 or more １８ cm －３ The following is included Laser diode.

2. The second conductive type cladding layer is made of silicon at 5×10 １５ cm －３ 1x10 or more １７ cm －３ Includes 10. The laser diode of claim 1.

3. The silicon is contained at the interface between the second conductive type clad layer and the second waveguide layer.

3. The laser diode according to claim 1.

4. At least the second conductive type cladding layer contains the silicon, and only a portion of the second conductive type cladding layer contains the silicon.

4. The laser diode according to claim 3.

5. The second conductive type cladding layer contains the silicon only in a region extending from an interface between the second conductive type cladding layer and the second waveguide layer toward the inside of the second conductive type cladding layer by 50 nm or less.

5. The laser diode according to claim 4.

6. The silicon is present at an interface between the nitride semiconductor substrate and the nitride buffer layer and at an interface between the nitride buffer layer and the first conductivity type cladding layer, respectively. １５ cm －３ 1x10 or more １８ cm －３ The following is included 10. The laser diode of claim 1.

7. The nitride buffer layer containing Al is AlN.

10. The laser diode of claim 1.

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

10. The laser diode of claim 1.

9. The first conductivity type cladding layer is Al ａ Ga （1-ａ） N (0.65<a≦0.9) 10. The laser diode of claim 1.

10. the thickness of the first conductivity type cladding layer is 250 nm or more and 500 nm or less; 10. The laser diode of claim 1.

11. The second conductive type cladding layer is Al ｅ Ga （1-ｅ） a second conductivity type vertical conduction layer containing N (0.1≦e≦1), having a composition gradient in which the Al composition e decreases with increasing distance from the nitride semiconductor substrate, and having a film thickness of less than 0.5 μm; ｆ Ga （1-ｆ） and a second conductivity type lateral conduction layer including N (0<f≦1).

10. The laser diode of claim 1.

12. The Al composition f of the second conductivity type lateral conduction layer at a surface facing the second conductivity type vertical conduction layer is greater than the minimum value of the Al composition e of the second conductivity type vertical conduction layer.

12. The laser diode according to claim 11.

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