WO2023163230A1

WO2023163230A1 - Laser diode

Info

Publication number: WO2023163230A1
Application number: PCT/JP2023/007424
Authority: WO
Inventors: 陽吉川; 梓懿張; 真希久志本; 千秋笹岡; 浩天野
Original assignee: 旭化成株式会社; 国立大学法人東海国立大学機構
Priority date: 2022-02-28
Filing date: 2023-02-28
Publication date: 2023-08-31

Abstract

Provided is a laser diode that relates to the reduction of an oscillating threshold current. The laser diode comprises a nitride semiconductor substrate containing Al, and a semiconductor layering part disposed on the nitride semiconductor substrate. The semiconductor layering part is formed by sequentially layering a first conductivity type cladding layer containing a first conductivity type nitride semiconductor layer, a first waveguide layer, a light emitting layer formed by a nitride semiconductor containing one or more quantum wells, a second waveguide layer, and a second conductivity type cladding layer containing a second conductivity type nitride semiconductor layer. The first conductivity type cladding layer is Al_aGa_(1-a)N (0.7<a<0.8), the first waveguide layer is Al_c1Ga_(1-c1)N (0.6<c1<0.7), the second waveguide layer is Al_c2Ga_(1-c2)N (0.6<c2<0.7), and the film thickness ratio T1/T2 of the first waveguide layer film thickness T1 and the second waveguide layer film thickness T2 is 0.3-0.7, inclusive.

Description

laser diode

This disclosure relates to laser diodes.

Conventionally, nitride semiconductors have been used as materials for forming light emitting diodes (LEDs) and laser diodes (LDs). Since nitride semiconductors have a recombination mode of direct transition, they are suitable as materials for LEDs and LDs in that high recombination efficiency and high optical gain can be obtained. As an example of a laser diode using such a nitride semiconductor, a technique for oscillating a current injection type laser diode in the ultraviolet region has been disclosed (for example, Non-Patent Document 1).

The UV laser diodes mentioned above are pulsed and require continuous wave for practical applications. This continuous oscillation requires reduction of the oscillation threshold current.
An object of the present disclosure is to provide a laser diode with reduced lasing threshold current.

In order to solve the above-described problems, a laser diode according to one aspect of the present disclosure includes a nitride semiconductor substrate containing Al, and a semiconductor lamination portion arranged on the nitride semiconductor substrate, wherein the semiconductor lamination portion is a first conductivity type clad layer disposed on a nitride semiconductor substrate and including a first conductivity type nitride semiconductor layer; a first waveguide layer disposed on the first conductivity type clad layer; a light-emitting layer disposed on the waveguide layer and formed of a nitride semiconductor including one or more quantum wells; a second waveguide layer disposed on the light-emitting layer; a second waveguide layer disposed on the second waveguide layer; a second-conductivity-type clad layer including a second-conductivity-type nitride semiconductor layer, wherein the first-conductivity-type clad layer is Al _a Ga _(1-a) N (0.7<a<0.8 ), the first waveguide layer is Al _c1 Ga _(1−c1) N (0.6<c1<0.7), and the second waveguide layer is Al _c2 Ga _(1−c2) N (0.6<c2<0.7), and the film thickness ratio T1/T2 between the film thickness T1 of the first waveguide layer and the film thickness T2 of the second waveguide layer is 0.3 or more and 0.7. It is below.
Note that the summary of the invention described above does not list all the features of the invention according to the present disclosure.

According to the present disclosure, it is possible to provide a laser diode capable of reducing the oscillation threshold current.

1 is a schematic cross-sectional view showing one configuration example of a laser diode according to an embodiment of the present disclosure; FIG. 1 is a plan view showing a configuration example of a laser diode according to an embodiment of the present disclosure; FIG.

Although the laser diode according to the present disclosure will be described below through embodiments, the following embodiments do not limit the invention according to the claims. Also, not all combinations of features described in the embodiments are essential for the solution of the invention.
Also, in the following description, "above" and "below" do not necessarily mean the vertical direction with respect to the ground. That is, the "up" and "down" directions are not limited to the direction of gravity. "Upper" and "lower" are merely expedient expressions specifying relative positional relationships among surfaces, films, substrates, etc., and do not limit the technical idea of the present invention. For example, if the paper surface is rotated 180 degrees, it goes without saying that "top" becomes "bottom" and "bottom" becomes "top".

1. Embodiment A laser diode according to an embodiment of the present disclosure will be described.
(1.1) Configuration of Laser Diode A laser diode according to the present embodiment includes a nitride semiconductor substrate containing Al and a semiconductor lamination portion arranged on the nitride semiconductor substrate. The semiconductor lamination portion is arranged on the nitride semiconductor substrate and includes a first conductivity type clad layer including a first conductivity type nitride semiconductor layer, and a first waveguide layer arranged on the first conductivity type clad layer. , a light-emitting layer disposed on the first waveguide layer and formed of a nitride semiconductor including one or more quantum wells; a second waveguide layer disposed on the light-emitting layer; and a second conductivity type clad layer disposed and including a second conductivity type nitride semiconductor layer. The first conductivity type clad layer is Al _a Ga _(1−a) N (0.7<a<0.8), and the first waveguide layer is Al _c1 Ga _(1−c1) N (0.8). 6<c1<0.7), the second waveguide layer is Al _c2 Ga _(1−c2) N (0.6<c2<0.7), and the thickness of the first waveguide layer is T1 and the film thickness T2 of the second waveguide layer, the film thickness ratio T1/T2 is 0.3 or more and 0.7 or less.
Each layer of the laser diode will be described in detail below.

<Nitride semiconductor substrate>
A nitride semiconductor substrate (hereinafter sometimes referred to as a substrate) contains a nitride semiconductor containing Al. A nitride semiconductor containing Al is, for example, AlN. That is, the substrate is preferably an AlN single crystal substrate. Also, the nitride semiconductor containing Al is not limited to AlN, and may be AlGaN, for example. For example, when the substrate is a nitride semiconductor single crystal substrate such as AlN or AlGaN, the difference in lattice constant from the nitride semiconductor layer formed on the substrate becomes small, and the nitride semiconductor layer is grown in a lattice matching system. This can reduce threading dislocations.
The threading dislocation density of the substrate is preferably 5×10 ⁴ cm ⁻² or less. In particular, from the viewpoint of reducing the oscillation threshold current, the threading dislocation density is more preferably 1×10 ³ or more and 1×10 ⁴ cm ⁻² or less.

Here, "including" in the expression "including a nitride semiconductor" means that the nitride semiconductor is mainly included in the layer, but the expression also includes cases where other elements are included. Specifically, a small amount of an element other than a nitride semiconductor (for example, Ga (when Ga is not the main element), In, As, P, or Sb, etc. is added in a few percent or less) to the composition of this layer. This expression also includes cases where minor changes are made. The term "includes" also has the same meaning in expressing the compositions of other layers. Also, the minor elements contained are not limited to those described above.

For example, the substrate preferably has a layer thickness of 100 μm or more and 600 μm or less. The plane orientation includes c-plane (0001), a-plane (11-20), m-plane (10-10), etc., but the c-plane (0001) substrate is more preferable. Furthermore, it can be formed on a plane inclined at some angle (for example, -4° to 4°, preferably -0.4° to 0.4°) from the c-plane (0001) normal direction, but this is not limited to

<Buffer layer>
The buffer layer is formed between the substrate and the clad layer of the first conductivity type, and is preferably formed over the entire surface of the substrate. By providing the buffer layer, a nitride semiconductor layer having a small difference in lattice constant and thermal expansion coefficient and few defects is formed on the buffer layer.
The buffer layer is preferably a nitride semiconductor layer containing Al. For example, AlN.

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

<First conductivity type cladding layer>
A first conductivity type clad layer is formed on the substrate. Here, for example, the term "on" in the expression "a clad layer of the first conductivity type is formed on the substrate" means that the clad layer of the first conductivity type is formed on one side of the substrate. do. The above expression also includes the case where another layer further exists between the substrate and the first-conductivity-type clad layer. The word "upper" has the same meaning also in relation between other layers. For example, even when a second conductivity type clad layer is formed on a first waveguide layer, which will be described later, through an electron blocking layer, the phrase "the second conductivity type clad layer is formed on the first waveguide layer" is used. included in the expression. Further, in the description of the present embodiment, "first conductivity type" and "second conductivity type" mean semiconductors exhibiting different conductivity types. , the other becomes p-type conductive.

The first conductivity type cladding layer is a nitride semiconductor layer containing Al and Ga. The first conductivity type cladding layer is made of Al _a Ga _(1-a) N (0<a<1), for example. This makes it possible to improve the crystallinity of the light-emitting layer and improve the light-emitting efficiency when the light-emitting layer is formed of a material corresponding to the bandgap energy of the deep ultraviolet region. From the viewpoint of achieving high luminous efficiency, the nitride semiconductor forming the first conductivity type clad layer is preferably a mixed crystal of AlN and GaN. Further, from the viewpoint of growing with perfect strain on the substrate, the first conductivity type clad layer is more preferably made of Al _a Ga _(1-a) N (0.6<a≦0.9). . From the viewpoint of improving the optical confinement coefficient, it is more preferably made of Al _a Ga _(1-a) N (0.7<a≦0.8). The Al composition of the first-conductivity-type cladding layer is preferably uniform in the film thickness direction, but is not limited to this. The average Al composition in the first-conductivity-type cladding layer is obtained by integrating the Al composition at a certain position over the film thickness range and then dividing it by the film thickness. For example, when the Al composition is linearly graded from 100% to 70% from the start position to the end position of the first-conductivity-type cladding layer, the average composition a' is 85%. Further, when 2/3 of the film thickness is 100% and 1/3 of the film thickness is 70%, the average composition a' is 90%.

For the purpose of controlling longitudinal conductivity, the first conductivity type clad layer may be a graded layer in which the Al composition increases with distance from the substrate. In this case, the Al composition described above can be limited to the Al composition obtained by averaging the Al composition at positions in the first conductivity type clad layer in the film thickness direction with respect to the thickness of the first conductivity type clad layer.

When the first-conductivity-type cladding layer is an n-type conductive semiconductor layer, it may contain group V elements other than N such as P, As, and Sb, and impurities such as C, H, F, O, Mg, and Si. Good, but the type of impurity element is not limited to this. From the viewpoint of reducing the electrical resistance and the difficulty 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 or more and 5×10 ¹⁹ cm. ^-3 is preferred.
The first conductivity type clad layer preferably has a layer thickness of 250 nm or more and 600 nm or less, and has a layer thickness of 300 nm or more and 450 nm or less, from the viewpoint of lattice relaxation in the first conductivity type clad layer and the film resistance. is more preferable.

<Light emitting layer>
The light emitting layer is a nitride semiconductor layer containing Al and Ga. _The nitride semiconductor included in the light-emitting layer is preferably a mixed crystal of AlN and GaN, for example, from the viewpoint of achieving high light- _emitting efficiency. be. From the viewpoint of lattice matching with the substrate, the quantum well layer of the light emitting layer is preferably Al _b Ga _(1-b) N (0.35<b<0.6). The light-emitting layer may have either a multi-quantum well structure or a single-layer quantum well structure, but the number of quantum well structures is preferably two to four. Moreover, from the viewpoint of the light emission efficiency of the light emitting layer, the film thickness of the quantum well layer is preferably 3 nm or more and 6 nm or less.
The light-emitting layer may contain group V elements other than N such as P, As, and Sb, and impurities such as C, H, F, O, Mg, and Si. do not have.

<Waveguide layer>
From the viewpoint of light confinement as a laser diode, the laser diode of this embodiment is formed above and below the light-emitting layer so as to sandwich the light-emitting layer, and has the effect of confining the light emitted from the light-emitting layer within the light-emitting layer. It may have layers. The waveguide layer is composed of a first waveguide layer arranged on the first conductivity type clad layer side with respect to the light emitting layer and a second waveguide layer arranged on the second conductivity type clad layer side with respect to the light emitting layer. It is preferably composed of two layers.
That is, the laser diode of this embodiment includes, for example, a first waveguide layer disposed between a first conductivity type clad layer and a light emitting layer to confine light in the light emitting layer, a second conductivity type clad layer, and a light emitting layer. a second waveguide layer disposed between the layers to confine light to the light emitting layer.

From the viewpoint of optical confinement, the waveguide layer is preferably a nitride semiconductor containing Al and Ga having a bandgap with higher energy than the light emitting layer. The waveguide layer preferably has an Al composition and thickness that increase the field intensity distribution of the light residing within the device and the overlap of the light emitting layer. From the viewpoint of carrier confinement in the light emitting layer, the first waveguide layer is Al _c1 Ga _(1−c1) N (0.6<c1<0.7), and the second waveguide layer is Al _c2 Ga _{(1 -c2)} N (0.6<c2<0.7) is preferred. For example, in the case of a light-emitting layer with an emission wavelength of 265 nm, the Al composition in the quantum well layer of the light-emitting layer is b=0.52, and c1 and c2 can be 0.63. From the viewpoint of light confinement and device resistance, it is preferable that the film thickness T1 of the first waveguide layer is 20 nm or more and 50 nm or less, and the film thickness T2 of the second waveguide layer is 50 nm or more and 90 nm or less. More preferably, the film thickness T1 of the first waveguide layer is 30 nm or more and 50 nm or less, and the film thickness T2 of the second waveguide layer is 60 nm or more and 80 nm or less. This makes it possible to more strongly overlap the asymmetric optical modes in the light-emitting layer. As a result, the optical confinement coefficient is further improved, and the oscillation current threshold can be reduced. Similarly, the film thickness ratio T1/T2 between the film thickness T1 of the first waveguide layer and the film thickness T2 of the second waveguide layer is preferably 0.3 or more and 0.7 or less. It is preferably 0.5 or more and 0.6 or less.

The waveguide layer may contain group V elements other than N, such as P, As, and Sb, and impurities such as C, H, F, O, Mg, and Si. isn't it.
The Al composition of each of the first waveguide layer and the second waveguide layer is preferably uniform in the film thickness direction, but is not limited to this. The Al composition of the second waveguide layer is higher than the Al composition of the first waveguide layer in order to avoid light absorption by the metal (for example, the second electrode) existing above the second conductivity type cladding layer, which will be described later. may be

<Second conductivity type clad layer>
The second-conductivity-type cladding layer is a nitride semiconductor layer formed on the light-emitting layer and containing Al and Ga having second-conductivity-type conductivity. The second-conductivity-type cladding layer is made of Al _d Ga _(1-d) N (0<d<1), for example. Further, when a waveguide layer (second waveguide layer) is provided on the light emitting layer, the second conductivity type cladding layer is formed on the waveguide layer (second waveguide layer). Thereby, the second-conductivity-type cladding layer can be easily lattice-matched with the light-emitting layer or the waveguide layer, and the threading dislocation density can be suppressed.

The second-conductivity-type cladding layer has conductivity sufficient to inject carriers (electrons or holes) into the light-emitting layer, and increases the electric field intensity distribution of the optical mode existing in the device and the overlap of the light-emitting layer. The conductivity type is not particularly limited as long as it is possible to increase the confinement of light (that is, to increase the optical confinement). From the viewpoint of enhancing optical confinement, the average Al composition d' of the second-conductivity-type clad layer is preferably larger than the average Al composition a' of the first-conductivity-type clad layer. More preferably, the average Al composition d' of the second-conductivity-type clad layer is 0.8 or more and 0.9 or less. This makes it possible to more strongly overlap the asymmetric optical modes in the light-emitting layer. As a result, the optical confinement coefficient is further improved, and the oscillation current threshold can be reduced. At this time, the average Al composition is obtained by integrating the Al composition at a certain position in the film thickness range and then dividing it by the film thickness. For example, when the Al composition is linearly graded from 100% to 70% from the start position to the end position of the second-conductivity-type clad layer, the average composition d' is 85%. Further, when 2/3 of the film thickness is 100% and 1/3 of the film thickness is 70%, the average composition d' is 90%.
From the viewpoint of relaxation, the film thickness of the second clad layer is preferably 300 nm or more and 400 nm or less.

From the viewpoint of injecting carriers into the light-emitting layer more efficiently, the second-conductivity-type cladding layer is inclined such that the Al composition e decreases with increasing distance from the substrate, that is, the Al composition e decreases in the direction away from the upper surface of the substrate. A composition gradient layer (second conductivity type vertical conduction layer) made of Al _e Ga _(1−e) N (0.1≦e≦1) and Al _f Ga _(1−f) N (0<f≦1) 1) and a lateral conductive layer of the second conductivity type including 1).
Also, the second conductivity type cladding layer may be, for example, p-type AlGaN doped with Mg. The second conductivity type cladding layer may contain, for example, group V elements other than N, such as P, As, and Sb, and impurities such as C, H, F, O, Mg, and Si. is not limited to this.
The second-conductivity-type vertical conduction layer and the second-conductivity-type horizontal conduction layer will be described below.

(Second conductivity type vertical conduction layer)
The second-conductivity-type vertical conduction layer is a layer forming a region of the second-conductivity-type clad layer on the light-emitting layer side.
The second-conductivity-type vertical conduction layer is a layer containing _AleGa _(1-e) N. The profile (slope) of the Al composition e in the second-conductivity-type vertical conduction layer may decrease continuously or may decrease intermittently. Here, "intermittently decreasing" means that a portion of the film of the second-conductivity-type vertical conduction layer includes a portion in which the Al composition e is the same (constant in the film thickness direction). . That is, the second-conductivity-type vertical conduction layer may include a portion where the Al composition e does not decrease in the direction away from the substrate, but does not include a portion where the Al composition e increases.

From the viewpoint of lattice matching, the film thickness of the second-conductivity-type vertical conduction layer is preferably 500 nm or less, more preferably 20 nm or more and 400 nm or less, and even more preferably 30 nm or more and 350 nm or less.

(Second conductivity type lateral conductive layer)
The second-conductivity-type lateral conduction layer is a layer forming a region of the second-conductivity-type cladding layer opposite to the light-emitting layer, and is formed on the second-conductivity-type vertical conduction layer.
The second conductivity type lateral conduction layer is a layer containing Al _f Ga _(1−f) N (0<f≦1). Here, it is preferable that the Al composition f of the surface of the second-conductivity-type horizontal conduction layer facing the second-conductivity-type vertical conduction layer is larger than the minimum value of the Al composition e of the second-conductivity-type vertical conduction layer.
From the viewpoint of facilitating quantum transmission of carriers passing through the second-conductivity-type lateral conducting layer, the thickness of the second-conductivity-type lateral conducting layer is preferably 20 nm or less, more preferably 10 nm or less, and 5 nm. More preferably:

When a second-conductivity-type contact layer, which will be described later, is provided on the second-conductivity-type lateral-conducting layer, the Al composition at the interface between the second-conductivity-type lateral-conducting layer and the second-conductivity-type contact layer is It is preferably less than the Al composition in the layer and fully strained relative to the substrate. In such a second-conductivity-type lateral conductive layer, the net internal electric field accumulated on the surface and near the surface of the second-conductivity-type lateral conductive layer becomes negative, and carriers are induced at the interface, thereby laterally Conductivity can be improved.

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 the carriers are efficiently generated. It has a good effect of injecting into the active layer in the light emitting layer. Therefore, the carrier injection efficiency of the laser diode can be increased by providing the vertical conduction layer of the second conductivity type on the light emitting layer.

In addition, the lateral conductive layer of the second conductivity type has the effect of widening the carrier distribution, which is narrowed by the electric field concentrated under the electrode, in the lateral direction (within the plane of the lateral conductive layer of the second conductivity type). Due to this effect, the second-conductivity-type horizontal conduction layer can increase the efficiency of carrier injection into the light-emitting layer in the same manner as the second-conductivity-type vertical conduction layer.

<Second conductivity type contact layer>
The semiconductor lamination portion of the laser diode of this embodiment may further include a second conductivity type contact layer disposed on the second conductivity type clad layer. The nitride semiconductor constituting the second-conductivity-type contact layer is preferably made of, for example, GaN, AlN, or InN, or a mixed crystal containing them, and more preferably a nitride semiconductor containing GaN.

The second conductivity type contact layer may contain V group elements other than N, such as P, As, and Sb, and impurities such as C, H, F, O, Mg, Si, and Be. Due to the versatility of the raw material gas, the impurity contained in the second conductivity type contact layer is preferably Mg. From the viewpoint of reducing the contact resistance, the Mg concentration is preferably 8×10 ¹⁹ cm ⁻³ or more and 5×10 ²¹ cm ⁻³ or less, and more preferably 5×10 ²⁰ cm ⁻³ or more and 5×10 ²¹ cm ⁻³ or less. It is more preferable to have

Further, the layer thickness of the second-conductivity-type contact layer is preferably 1 nm or more and 20 nm or less. The carrier injection efficiency of the light-emitting layer improves as the layer thickness of the second-conductivity-type contact layer decreases, and the carrier injection efficiency decreases as the layer thickness increases.

<Electron blocking layer>
The semiconductor lamination portion of the light emitting layer of the present embodiment may further have an electron blocking layer above the light emitting layer and 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 conduction layer. It can also be set between
The layer thickness of the electron blocking layer is preferably 30 nm or less, more preferably 20 nm or less so that carriers (holes) can easily quantum penetrate the electron blocking layer.

<Electrode>
A laser diode can emit light or oscillate by injecting a current through a second electrode arranged on a second-conductivity-type clad layer and a first electrode arranged on a first-conductivity-type clad layer. At this time, the first electrode is formed so as to be in electrical contact with the clad layer of the first conductivity type, and the second electrode is formed so as to be in electrical contact with the clad layer of the second conductivity type.
The first electrode can be arranged, for example, on the back side of the substrate. Also, the first electrode is arranged on the first conductivity type cladding layer exposed by removing the layer above the first conductivity type cladding layer of the semiconductor lamination portion by chemical etching or dry etching, for example. That is, the first electrode is arranged on a region in which the mesa structure is not formed in the first-conductivity-type cladding layer.

When the first conductivity type clad layer is an n-type clad layer, the first electrode is Al, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Co, Rh, Ir, Ni, Pd, Pt. , Cu, Ag, Au, Zr, etc., a mixed crystal thereof, or a conductive oxide such as ITO or Ga ₂ O ₃ .
When the first conductivity type clad layer is a p-type clad layer, the first electrode is Ni, Au, Pt, Ag, Rh, Pd, Pt, Cu, Al, Ti, Zr, Hf, V, Nb, Ta, Cr , Mo, W, Co, Ir, and Zr, or mixed crystals thereof, or conductive oxides such as ITO or Ga ₂ O ₃ .

When the second conductivity type clad layer is an n-type clad layer, the second electrode is Al, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Co, Rh, Ir, Ni, Pd, Pt. , Cu, Ag, Au, Zr, etc., a mixed crystal thereof, or a conductive oxide such as ITO or Ga ₂ O ₃ .
When the second conductivity type clad layer is a p-type clad layer, the second electrode is Ni, Au, Pt, Ag, Rh, Pd, Pt, Cu, Al, Ti, Zr, Hf, V, Nb, Ta, Cr , Mo, W, Co, Ir, and Zr, or mixed crystals thereof, or conductive oxides such as ITO or Ga ₂ O ₃ .

The arrangement regions and shapes of the first electrode and the second electrode are the same as those of the first-conductivity-type clad layer and the second-conductivity-type clad layer (the second-conductivity-type contact layer when the second-conductivity-type contact layer is provided). There is no limitation as long as electrical contact is obtained.

(1.2) Manufacturing Method of Ultraviolet Laser Diode The laser diode of the present embodiment is manufactured through steps of forming layers on a substrate.

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

(Formation of semiconductor laminated portion)
Each layer of the semiconductor laminate formed on the substrate is formed by, for example, a molecular beam epitaxy (MBE) method, a hydride vapor phase epitaxy (HVPE) method, or a metal organic chemical vapor deposition (MOCVD) method. It can be formed by a method or the like.
Here, among the layers formed on the substrate, the nitride semiconductor layer is, for example, an Al raw material containing trimethylaluminum (TMAl), a Ga raw material containing trimethylgallium (TMGa) or triethylgallium (TEGa), or ammonia ( NH ₃ ) can be used as the N source material.

A first conductivity type clad layer containing a first conductivity type nitride semiconductor is formed on a buffer layer formed on a substrate. Next, a light-emitting layer is formed on the first-conductivity-type clad layer using a nitride semiconductor (such as AlGaN) including one or more quantum wells, and a second-conductivity-type clad layer is formed on the light-emitting layer.
If necessary, waveguide layers made of a nitride semiconductor such as AlGaN may be formed above and below the light emitting layer. Further, an intermediate layer made of a nitride semiconductor such as AlGaN may be formed between the second-conductivity-type clad layer and the waveguide, or a second-conductivity-type nitride semiconductor containing GaN or the like may be formed on the second-conductivity-type clad layer. A contact layer may be provided, and an electron blocking layer may be formed above the light emitting layer.

A laser diode is manufactured through a process (mesa structure forming process) of removing unnecessary portions of each layer of a semiconductor laminate formed on a substrate by etching. The removal of unnecessary portions of each layer of the semiconductor laminate can be performed by, for example, inductively coupled plasma (ICP) etching or the like.
In the mesa structure forming step, unnecessary portions of each layer of the conductor laminate are removed by etching, thereby partially exposing the first conductivity type clad layer.

(Formation of electrodes)
Also, the laser diode can be manufactured through a process of forming electrodes. Electrodes such as the first electrode and the second electrode are formed by various methods of evaporating metal by electron beam evaporation (EB), such as resistance heating evaporation, electron gun evaporation, or sputtering. is not limited. Each electrode may be formed as a single layer, or may be formed by laminating a plurality of layers. Further, each electrode may be subjected to heat treatment in an atmosphere of oxygen, nitrogen, air, or the like after the layer is formed.
Finally, the substrate on which each layer is formed through the above steps is divided into individual pieces by dicing to manufacture laser diodes.

Specifically, a first electrode is formed on the surface of the first-conductivity-type clad layer. Also, the second electrode is formed on the uppermost layer (for example, the second-conductivity-type clad layer) of the mesa structure formed in part of the semiconductor laminate.
As described above, according to the laser diode manufacturing method according to the present embodiment, the oscillation threshold current density can be reduced, and a long-life laser diode can be manufactured.

2. Method for Measuring Physical Properties of Laser Diode The physical properties of the laser diode described above can be measured as follows.

(Method for measuring layer thickness)
The layer thickness of each layer constituting the laser diode is 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 length measurement function of the TEM. can. As a measuring method, first, a TEM is used to observe a cross section perpendicular to the main surface of the substrate of the laser diode. Specifically, for example, the observation width is defined as a range of 2 μm or more in a direction parallel to the main surface of the substrate in a TEM image showing a cross section perpendicular to the main surface of the substrate of the laser diode. In this observation width range, a contrast is observed at the interface between the two layers with different compositions, so the thickness up to this interface is observed in a continuous observation area with a width of 200 nm. The layer thickness of each layer can be obtained by calculating the average value of the thickness of each layer included in the observation area of 200 nm width from five points arbitrarily extracted from the observation width of 2 μm or more.

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

(Method for measuring atomic concentration of each layer)
Methods for measuring the atomic concentration contained in each layer constituting a laser diode include reciprocal space mapping (RSM) by X-ray diffraction (XRD). Specifically, by analyzing the reciprocal lattice mapping data in the vicinity of the diffraction peak obtained with the asymmetric plane as the diffraction plane, the lattice relaxation rate and Al composition for the underlayer can be obtained. Examples of diffraction planes include the (10-15) plane and the (20-24) plane.
In addition, layers and regions where sufficient reflection intensity cannot be obtained by XRD, such as the light emitting layer, the gradient layer, and the hillocks formed in each layer, are X-ray photoelectron spectroscopy (XPS), energy dispersive X It can be measured by line spectroscopy (EDX: Energy Dispersive X-ray spectroscopy) and electron energy-loss spectroscopy (EELS: Electron Energy-Loss Spectroscopy).

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, in a sliced sample used for TEM observation, etc., an energy loss spectrum of the intensity of a transmitted electron beam is measured and analyzed. Using the fact that the peak position appearing near the energy loss of 20 eV changes according to the composition of each layer, the composition can be obtained from the peak position.
In the same manner as the layer thickness calculation method by TEM observation described above, the average value of the Al composition at an observation width of 200 nm is calculated from 5 points arbitrarily extracted from the observation area of 2 μm or more to obtain the Al composition of each layer.

EDX measures and analyzes the characteristic X-rays generated by the electron beam in the thinned sample used for the above-mentioned TEM observation. In the same manner as the layer thickness calculation method by TEM observation described above, the average value of the Al composition at an observation width of 200 nm is calculated from 5 points arbitrarily extracted from the observation area of 2 μm or more to obtain the Al composition of each layer.

With XPS, evaluation in the depth direction is possible by performing XPS measurement while performing sputter etching using an ion beam. Ar + is generally used for the ion beam, but other ion species such as Ar cluster ions may be used as long as the ions can be irradiated by an etching ion gun mounted on the XPS apparatus. The XPS peak intensities of Al, Ga, and N are measured and analyzed to obtain the depth direction distribution of the Al composition of each layer. Instead of sputter etching, the laser diode may be obliquely polished so that the cross section perpendicular to the main surface of the substrate is enlarged and exposed, and the exposed cross section may be measured by XPS.

The composition of each layer can be measured not only by XPS but also by using Auger Electron Spectroscopy (AES). In this case, the composition can be measured by measurement by Auger electron spectroscopy on a section exposed by sputter etching or oblique polishing. The composition of each layer can also be measured by SEM-EDX measurement of a section exposed by oblique polishing.

(Application fields of ultraviolet laser diodes)
The laser diode according to the present disclosure is applicable to devices in, for example, the medical/life science field, the environmental field, the industrial/industrial field, the life/home appliance field, the agricultural field, and other fields. Laser diodes are used in equipment for synthesizing and decomposing drugs or chemical substances, sterilizing equipment for liquids, gases, and solids (containers, food, medical equipment, etc.), cleaning equipment for semiconductors, etc., equipment for surface modification of films, glass, metals, etc., semiconductors・FPD (Flat Panel Display) ・PCB (Printed Wiring Board) ・Exposing equipment for manufacturing other electronic products, printing/coating equipment, adhesive/sealing equipment, transfer/molding equipment for film/pattern/mock-up, banknote/scratches・Applicable to measuring and testing devices for blood, chemical substances, etc.

Examples of liquid sterilizers include automatic ice makers, ice trays and ice storage containers in refrigerators, water supply tanks for ice makers, freezers, ice makers, humidifiers, dehumidifiers, cold water tanks, hot water tanks, and flow paths of water servers. Piping, stationary water purifiers, portable water purifiers, water supply equipment, water heaters, waste water treatment equipment, disposers, waste water traps for toilet bowls, washing machines, dialysis water sterilization modules, peritoneal dialysis connector sterilizers, disaster water storage systems, etc. are listed, but are not limited to these.

Examples of gas sterilizers include air purifiers, air conditioners, ceiling fans, floor or bedding vacuum cleaners, futon dryers, shoe dryers, washing machines, clothes dryers, indoor germicidal lamps, and storage ventilation. Examples include, but are not limited to, systems, shoeboxes, chests of drawers, and the like.
Examples of solid sterilizers (including surface sterilizers) include vacuum packers, belt conveyors, hand tool sterilizers for medical, dental, barber and beauty salon use, toothbrushes, toothbrush cases, chopstick cases, cosmetic pouches, Drain lids, local washes of toilet bowls, toilet bowl lids, etc., but not limited to these.

3. Specific Example of Laser Diode Hereinafter, the laser diode of the present embodiment will be described more specifically with reference to FIGS. 1 and 2. FIG. The detailed configuration of each layer in the following embodiments is as described above.
FIG. 1 is a schematic cross-sectional view of a laser diode 1 according to this embodiment. FIG. 2 is a plan view of the laser diode 1 according to this embodiment. As shown in FIG. 1, the laser diode 1 includes a substrate 11, a semiconductor lamination portion 10 arranged on the substrate 11, a first electrode 12, and a second electrode 13. As shown in FIG. The semiconductor lamination portion 10 includes a first conductivity type cladding layer 101 having n-type conductivity, a first waveguide layer 102, a light emitting layer 103, a second waveguide layer 104, and a second waveguide layer 104 having p-type conductivity. A conductive clad layer 105 and a contact layer 106 are provided.

4. Effects The laser diode described above has the following effects.
(1) A laser diode according to the present disclosure includes a nitride semiconductor substrate containing Al and a semiconductor lamination portion arranged on the nitride semiconductor substrate, the semiconductor lamination portion being arranged on the nitride semiconductor substrate, a first conductivity type cladding layer including a first conductivity type nitride semiconductor layer; a first waveguide layer disposed on the first conductivity type cladding layer; and one or more waveguide layers disposed on the first waveguide layer a light emitting layer formed of a nitride semiconductor including a quantum well of; a second waveguide layer disposed on the light emitting layer; and a nitride semiconductor layer of a second conductivity type disposed on the second waveguide layer and a second conductivity type clad layer comprising: the first conductivity type clad layer is Al _a Ga _(1−a) N (0.7<a<0.8); , Al _c1 Ga _(1−c1) N (0.6<c1<0.7), and the second waveguide layer is Al _c2 Ga _(1−c2) N (0.6<c2<0.7) , and the film thickness ratio T1/T2 between the film thickness T1 of the first waveguide layer and the film thickness T2 of the second waveguide layer is 0.3 or more and 0.7 or less.
This makes it possible to improve the optical confinement factor and reduce the oscillation threshold current density.

(2) In the laser diode of the present disclosure, it is preferable that the film thickness T1 of the first waveguide layer is 20 nm or more and 50 nm or less, and the film thickness T2 of the second waveguide layer is 50 nm or more and 90 nm or less.
This makes it possible to improve the optical confinement factor and reduce the oscillation threshold current density.

(3) In the laser diode of the present disclosure, the first conductivity type clad layer preferably has a thickness of 250 nm or more and 500 nm or less.
As a result, a nitride semiconductor laminate that does not relax can be obtained, the luminous efficiency can be improved, and the oscillation threshold current density can be reduced.

(4) In the laser diode of the present disclosure, the second conductivity type clad layer is Al _d Ga _(1−d) N (0<d<1), and the average composition d′ is the average of the first conductivity type clad layer It is preferably larger than the Al composition a'.
This makes it possible to improve the optical confinement factor and reduce the oscillation threshold current density.

(5) In the laser diode of the present disclosure, it is preferable that the film thickness of the second-conductivity-type clad layer is 300 nm or more and 400 nm or less.
This makes it possible to improve the optical confinement factor and reduce the oscillation threshold current density.

(6) In the laser diode of the present disclosure, the quantum well layer of the light-emitting layer is Al _b Ga _(1-b) N (0.4<b<0.6) and has a thickness of 3 nm or more and 6 nm or less. , preferably has a multiple quantum well structure of two to four layers.
As a result, a nitride semiconductor laminate that does not relax can be obtained, the luminous efficiency can be improved, and the oscillation threshold current density can be reduced.

(7) In the laser diode of the present disclosure, the nitride semiconductor substrate is preferably an AlN single crystal substrate.
As a result, the lattice constant difference between the substrate and the nitride semiconductor layer formed on the upper side of the substrate is reduced, and the nitride semiconductor layer is grown in a lattice matching system, thereby reducing threading dislocations and increasing stability. A high nitride semiconductor layer can be formed.

(8) The laser diode of the present disclosure includes a second conductivity type contact layer disposed on the second conductivity type cladding layer and formed of a nitride semiconductor containing GaN, wherein the second conductivity type cladding layer is made of Al A first film containing _e Ga _(1−e) 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. It is preferable to have a two-conductivity-type vertical conduction layer and a second-conductivity-type horizontal conduction layer containing Al _f Ga _(1−f) N (0<f≦1). This makes it possible to inject carriers into the light-emitting layer more efficiently, improve the light-emitting efficiency, and reduce the oscillation threshold current density.

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

<Example 1>
A (0001) plane AlN single crystal substrate having a thickness of 550 μm was used as the substrate.
Next, an AlN layer as a buffer layer was formed on the substrate. The AlN layer was formed with a thickness of 500 nm under an environment of 1200°C. At this time, the ratio (V/III ratio) between the supply rate of the group III element source gas and 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. Also, trimethylaluminum (TMAl) was used as an Al raw material. Ammonia (NH ₃ ) was used as the N raw material.

A clad layer of the first conductivity type was formed on this substrate. The first-conductivity-type cladding layer was an n-type AlGaN layer (Al: 75%, ie, an Al _0.75 Ga _0.25 N layer) using Si as a dopant impurity. The first conductivity type cladding layer was formed at a temperature of 1080° C., a degree of vacuum of 50 mbar and a V/III ratio of 4000 to a thickness of 400 nm. The growth rate of the first conductivity type clad layer at this time was 0.4 μm/hr. Also, trimethylaluminum (TMAl) was used as an Al raw material. Also, triethylgallium (TEGa) was used as a Ga source. Ammonia (NH ₃ ) was used as the N raw material. Also, monosilane (SiH ₄ ) was used as the Si raw material.

Subsequently, an n-type waveguide layer as a first waveguide layer was formed on the first conductivity type clad layer. The n-type waveguide layer was an AlGaN layer (Al: 63%, ie Al _0.63 Ga _0.37 N layer) containing no dopant. The n-type waveguide layer was formed with a thickness of 40 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 at this time was 0.35 μm/hr. Also, trimethylaluminum (TMAl) was used as an Al raw material. Also, triethylgallium (TEGa) was used as a Ga source. Ammonia (NH ₃ ) was used as the N raw material.

Subsequently, a light emitting layer was formed on the first waveguide layer. The light-emitting layer was formed by forming a film so as to have a multi-quantum well structure in which two periods of quantum well layers and barrier layers were laminated. Here, the quantum well layer was an AlGaN layer (Al: 52%, ie Al _0.52 Ga _0.48 N layer) having a thickness of 4.5 nm. Also, the barrier layer having a thickness of 6.0 nm was an AlGaN layer (Al: 63%, that is, an Al _0.63 Ga _0.37 N layer).
The light-emitting layer was formed under the conditions that the degree of vacuum was set to 50 mbar and the V/III ratio was set to 4000. The growth rate of the quantum well layer at this time was 0.18 μm/hr. Also, the growth rate of the barrier layer was 0.15 μm/hr.

Subsequently, a p-type waveguide layer as a second waveguide layer was formed on the light emitting layer. The p-type waveguide layer was an AlGaN layer (Al: 63%, ie Al _0.63 Ga _0.37 N layer) containing no dopant. The p-type waveguide layer was formed at a temperature of 1080° C., a degree of vacuum of 50 mbar and a V/III ratio of 4000 to a thickness of 70 nm. The growth rate of the p-type waveguide layer at this time was 0.35 μm/hr. Also, trimethylaluminum (TMAl) was used as an Al raw material. Also, triethylgallium (TEGa) was used as a Ga source.

Subsequently, a second conductivity type clad layer was formed on the p-type waveguide layer. The second-conductivity-type cladding layer has a laminated structure including a second-conductivity-type vertical conduction layer and a second-conductivity-type horizontal conduction layer, and is a graded layer with a graded Al composition ratio. The vertical conduction layer of the second conductivity type was an AlGaN layer having a layer thickness of 330 nm and having a distribution of Al composition in the direction away from the substrate and varying from Al = 1.0 to 0.7. The second-conductivity-type clad layer was formed at a temperature of 1,080° C. under the conditions of a degree of vacuum of 50 mbar and a V/III ratio of 4,000. The growth rate of the second conductivity type clad layer at this time was 0.3 to 0.5 μm/hr. Also, trimethylaluminum (TMAl) was used as an Al raw material. Also, triethylgallium (TEGa) was used as a Ga source. The lateral conduction layer of the second conductivity type was an AlGaN layer with Al=0.8 and a layer thickness of 5 nm.
At this time, the average Al composition d' in the second-conductivity-type clad layer was 0.85, which was larger than the average Al composition a' in the first-conductivity-type clad layer.

Subsequently, a p-type contact layer as a second conductivity type contact layer was formed on the second conductivity type cladding layer. Here, the p-type contact layer was formed of an AlGaN layer and a GaN layer. The AlGaN layer was a p-type nitride semiconductor layer with a layer thickness of 30 nm, using Mg as a dopant impurity, having an Al composition distribution in the direction away from the substrate and varying from Al=0.7 to 0.4. Also, the GaN layer was formed of GaN (that is, Al: 0%) with a thickness of 10 nm.
The second conductivity type contact layer was formed at a temperature of 950.degree. The growth rate of the second conductivity type contact layer at this time was 0.2 μm/hr.

As described above, a semiconductor lamination portion was formed on the AlN substrate. When the reciprocal lattice mapping measurement by XRD was performed on this semiconductor lamination portion, it was found that the semiconductor lamination portion undergoes pseudomorphic growth without relaxation up to the contact layer of the second conductivity type.

The semiconductor lamination portion formed as described above was annealed at 700° C. for 10 minutes or longer in an N ₂ atmosphere to further reduce the resistance of the second conductivity type contact layer. By performing dry etching using ICP with a gas containing Cl ₂ , a mesa structure with the first conductivity type clad layer exposed was formed.
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 in the <1-100> direction of the mesa structure is the distance between the resonator mirror end faces in plan view, and the length in the <11-20> direction is the distance between the side surfaces of the mesa structure. is.

On the contact layer of the second conductivity type in the mesa structure, Ni and Au were sequentially formed into films in a rectangular shape elongated in the <1-100> direction to form a plurality of electrode metal regions to form a p-type second electrode. At this time, the width of the second electrode was 5 μm and the length was 700 μm. Further, in the region where the n-type cladding layer of the mesa structure is exposed, V, Al, Ni, Ti and Au are deposited in order in a rectangular shape elongated in the <1-100> direction to form a plurality of electrode metal regions. It was used as the first electrode of the mold. An RTA apparatus was used to anneal the first electrode and the second electrode at 750° C. for 60 seconds in a nitrogen atmosphere.

Furthermore, in the electrode metal region, the substrate was divided into stripes by cleaving in parallel in the <11-20> direction multiple times to form singulated laser diodes. The length of the mesa structure after division in the <1-100> direction was 600 μm.
When the laser diode thus obtained was subjected to current-edge emission intensity measurement by current injection, the threshold voltage was 12.0 V and the oscillation threshold current density was 7.5 kA/cm ² .

<Example 2>
The laser diode of Example 2 was produced in the same manner as in Example 1 except that the first waveguide layer and the second waveguide layer were AlGaN layers (Al: 61%, that is, Al _0.61 Ga _0.39 N layers). formed.
When the laser diode thus obtained was subjected to current-edge emission intensity measurement by current injection, the threshold voltage was 11.5 V and the oscillation threshold current density was 8.5 kA/cm ² .

<Example 3>
The laser diode of Example 3 was manufactured in the same manner as in Example 1 except that the first waveguide layer and the second waveguide layer were AlGaN layers (Al: 66%, that is, Al _0.66 Ga _0.34 N layers). formed. When the laser diode thus obtained was subjected to current-edge emission intensity measurement by current injection, the threshold voltage was 12.5 V and the oscillation threshold current density was 7.2 kA/cm ² .

<Example 4>
The laser diode of Example 4 was produced in the same manner as in Example 1 except that the first waveguide layer and the second waveguide layer were AlGaN layers (Al: 69%, that is, Al _0.69 Ga _0.31 N layers). formed.
When the laser diode thus obtained was subjected to current-edge emission intensity measurement by current injection, the threshold voltage was 12.9 V and the oscillation threshold current density was 7.0 kA/cm ² .

<Example 5>
A laser diode of Example 5 was formed in the same manner as in Example 1 except that the film thickness T1 of the first waveguide layer was changed to 23 nm and the film thickness ratio T1/T2 was set to 0.33.
When the laser diode thus obtained was subjected to current-edge emission intensity measurement by current injection, the threshold voltage was 12.0 V and the oscillation threshold current density was 8.8 kA/cm ² .

<Example 6>
A laser diode of Example 6 was formed in the same manner as in Example 1 except that the film thickness T1 of the first waveguide layer was changed to 33 nm and the film thickness ratio T1/T2 was set to 0.47.
When the laser diode thus obtained was subjected to current-edge emission intensity measurement by current injection, the threshold voltage was 12.0 V and the oscillation threshold current density was 8.2 kA/cm ² .

<Example 7>
A laser diode of Example 7 was formed in the same manner as in Example 1 except that the film thickness T1 of the first waveguide layer was changed to 47 nm and the film thickness ratio T1/T2 was set to 0.67.
When current-edge emission intensity measurement was performed on the laser diode thus obtained by current injection, the threshold voltage was 12.0 V and the oscillation threshold current density was 8.3 kA/cm ² .

<Example 8>
Conducted in the same manner as in Example 1 except that the film thickness T1 of the first waveguide layer was changed to 35 nm, the film thickness T2 of the second waveguide layer was changed to 55 nm, and the film thickness ratio T1/T2 was changed to 0.64. A laser diode of Example 8 was formed.
When the laser diode thus obtained was subjected to current-edge emission intensity measurement by current injection, the threshold voltage was 11.6 V and the oscillation threshold current density was 9.3 kA/cm ² .

<Example 9>
A laser diode of Example 9 was formed in the same manner as in Example 1 except that the film thickness T2 of the second waveguide layer was changed to 85 nm and the film thickness ratio T1/T2 was set to 0.47.
When the laser diode thus obtained was subjected to current-edge emission intensity measurement by current injection, the threshold voltage was 12.7 V and the oscillation threshold current density was 7.2 kA/cm ² .

<Example 10>
A laser diode of Example 10 was formed in the same manner as in Example 1 except that the first conductivity type cladding layer was an AlGaN layer (Al: 72%, ie, an Al _0.72 Ga _0.28 N layer).
When the laser diode thus obtained was subjected to current-edge emission intensity measurement by current injection, the threshold voltage was 10.0 V and the oscillation threshold current density was 9.0 kA/cm ² .

<Example 11>
A laser diode of Example 11 was formed in the same manner as in Example 1 except that the first conductivity type cladding layer was an AlGaN layer (Al: 78%, ie, an Al _0.78 Ga _0.22 N layer).
When the laser diode thus obtained was subjected to current-edge emission intensity measurement by current injection, the threshold voltage was 14.0 V and the oscillation threshold current density was 7.2 kA/cm ² .

<Example 12>
A laser diode of Example 12 was formed in the same manner as in Example 1 except that the light emitting layer was an AlGaN layer (Al: 43%, that is, an Al _0.43 Ga _0.57 N layer).
When the laser diode thus obtained was subjected to current-edge emission intensity measurement by current injection, the threshold voltage was 11.5 V and the oscillation threshold current density was 6.5 kA/cm ² .

<Example 13>
A laser diode of Example 13 was formed in the same manner as in Example 1 except that the light emitting layer was an AlGaN layer (Al: 58%, ie, an Al _0.58 Ga _0.42 N layer).
When the laser diode thus obtained was subjected to current-edge emission intensity measurement by current injection, the threshold voltage was 12.5 V and the oscillation threshold current density was 8.5 kA/cm ² .

<Example 14>
A laser diode of Example 14 was formed in the same manner as in Example 1 except that the number of periods of the light emitting layer was 3, that is, the number of quantum well structures was 3.
When the laser diode thus obtained was subjected to current-edge emission intensity measurement by current injection, the threshold voltage was 11.5 V and the oscillation threshold current density was 7.1 kA/cm ² .

<Example 15>
A laser diode of Example 15 was formed in the same manner as in Example 1 except that the periodicity of the light emitting layer was 4, that is, the number of quantum well layers was 4.
When the laser diode thus obtained was subjected to current-edge emission intensity measurement by current injection, the threshold voltage was 11.0 V and the oscillation threshold current density was 6.8 kA/cm ² .

<Example 16>
A laser diode of Example 16 was formed in the same manner as in Example 1, except that the film thickness of the light emitting layer was 3.5 nm.
When the laser diode thus obtained was subjected to current-edge emission intensity measurement by current injection, the threshold voltage was 11.3 V and the oscillation threshold current density was 8.0 kA/cm ² .

<Example 17>
A laser diode of Example 17 was formed in the same manner as in Example 1, except that the thickness of the light emitting layer was 5.5 nm.
When the laser diode thus obtained was subjected to current-edge emission intensity measurement by current injection, the threshold voltage was 10.4 V and the oscillation threshold current density was 7.1 kA/cm ² .

<Example 18>
A laser diode of Example 18 was formed in the same manner as in Example 1 except that the film thickness of the second-conductivity-type cladding layer was 300 nm.
Current-edge emission intensity measurement by current injection was performed on the laser diode thus obtained, and the threshold voltage was 10.5 V, and the oscillation threshold current density was 8.3 kA/cm ² .

<Example 19>
A laser diode of Example 19 was formed in the same manner as in Example 1, except that the thickness of the second-conductivity-type cladding layer was set to 250 nm.
When the laser diode thus obtained was subjected to current-edge emission intensity measurement by current injection, the threshold voltage was 10.2 V and the oscillation threshold current density was 9.1 kA/cm ² .

<Example 20>
A laser diode of Example 20 was formed in the same manner as in Example 1, except that the film thickness of the second-conductivity-type clad layer was 400 nm.
When the laser diode thus obtained was subjected to current-edge emission intensity measurement by current injection, the threshold voltage was 12.6 V and the oscillation threshold current density was 7.0 kA/cm ² .

<Example 21>
A laser diode of Example 21 was formed in the same manner as in Example 1 except that the film thickness of the second-conductivity-type cladding layer was set to 450 nm.
When the laser diode thus obtained was subjected to current-edge emission intensity measurement by current injection, the threshold voltage was 12.9 V and the oscillation threshold current density was 7.1 kA/cm ² .

<Example 22>
The same procedure as in Example 1 was performed except that the second conductivity type vertical conduction layer was an AlGaN layer with a layer thickness of 330 nm, which had an Al composition distribution in the direction away from the substrate and varied from Al = 1.0 to 0.5. A laser diode of Example 22 was formed.
When the laser diode thus obtained was subjected to current-edge emission intensity measurement by current injection, the threshold voltage was 10.0 V and the oscillation threshold current density was 9.0 kA/cm ² .

<Comparative Example 1>
A laser diode of Comparative Example 1 was formed in the same manner as in Example 1 except that the first waveguide layer was an AlGaN layer (Al: 55%, that is, an Al _0.55 Ga _0.45 N layer).
When the laser diode thus obtained was subjected to current-edge emission intensity measurement by current injection, the threshold voltage was 11.8 V and the oscillation threshold current density was 11.7 kA/cm ² .

<Comparative Example 2>
A laser diode of Comparative Example 2 was formed in the same manner as in Example 1 except that the first waveguide layer was an AlGaN layer (Al: 75%, ie, an Al _0.75 Ga _0.25 N layer).
When the laser diode thus obtained was subjected to current-edge emission intensity measurement by current injection, the threshold voltage was 12.2 V and the oscillation threshold current density was 12.1 kA/cm ² .

<Comparative Example 3>
A laser diode of Comparative Example 3 was formed in the same manner as in Example 1 except that the second waveguide layer was an AlGaN layer (Al: 55%, ie, an Al _0.55 Ga _0.45 N layer).
When the laser diode thus obtained was subjected to current-edge emission intensity measurement by current injection, the threshold voltage was 11.8 V and the oscillation threshold current density was 11.9 kA/cm ² .

<Comparative Example 4>
A laser diode of Comparative Example 4 was formed in the same manner as in Example 1 except that the second waveguide layer was an AlGaN layer (Al: 75%, ie, an Al _0.75 Ga _0.25 N layer).
When the laser diode thus obtained was subjected to current-edge emission intensity measurement by current injection, the threshold voltage was 12.2 V and the oscillation threshold current density was 12.1 kA/cm ² .

<Comparative Example 5>
A laser diode of Comparative Example 5 was formed in the same manner as in Example 1 except that the first conductivity type cladding layer was an AlGaN layer (Al: 65%, ie, an Al _0.65 Ga _0.35 N layer).
When the laser diode thus obtained was subjected to current-edge emission intensity measurement by current injection, the threshold voltage was 9.0 V and the oscillation threshold current density was 12.0 kA/cm ² .

<Comparative Example 6>
A laser diode of Comparative Example 6 was formed in the same manner as in Comparative Example 1 except that the first conductivity type cladding layer was an AlGaN layer (Al: 85%, ie, an Al _0.85 Ga _0.15 N layer).
When the laser diode thus obtained was subjected to current-edge emission intensity measurement by current injection, the threshold voltage was 17.0 V and the oscillation threshold current density was 12.0 kA/cm ² .

<Comparative Example 7>
Comparative Example 7 was carried out in the same manner as in Example 1 except that the film thickness T1 of the first waveguide layer was 25 nm, the film thickness T2 of the second waveguide layer was 100 nm, and the film thickness ratio T1/T2 was 0.25. of laser diodes were formed.
When the laser diode thus obtained was subjected to current-edge emission intensity measurement by current injection, the threshold voltage was 12.0 V and the oscillation threshold current density was 10.9 kA/cm ² .

<Comparative Example 8>
The laser of Comparative Example 8 was produced in the same manner as in Example 1 except that the film thickness T1 of the first waveguide layer was 50 nm, the film thickness T2 of the second waveguide layer was 50 nm, and the film thickness ratio T1/T2 was 1. formed a diode.
When the laser diode thus obtained was subjected to current-edge emission intensity measurement by current injection, the threshold voltage was 12.0 V and the oscillation threshold current density was 11.8 kA/cm ² .

Table 1 below shows the evaluation results of each example and each comparative example.

As shown in Table 1, the Al composition a of the first conductivity type cladding layer satisfies 0.7<a<0.8, and the Al composition c1 of the first waveguide layer satisfies 0.6<c1<0.7. , the Al composition c2 of the second waveguide layer satisfies 0.6<c2<0.7, and the film thickness ratio between the film thickness T1 of the first waveguide layer and the film thickness T2 of the second waveguide layer is T1/ In the laser diodes of the comparative examples, which include a layer in which T2 does not satisfy 0.3 or more and 0.7 or less, the oscillation threshold current density was 10.9 kA/cm ² or more.
On the other hand, the laser diodes of the examples, in which each layer satisfies the above range, had an oscillation threshold current density of less than 10 kA/cm ² , which was lower than that of the laser diodes of the comparative examples.

Further, as shown in Examples 1 to 4, when the Al composition c1 of the first waveguide layer and the Al composition c2 of the second waveguide layer are within the ranges described above, the Al composition c1 and the Al composition c2 are The higher the value, the stronger the light confinement effect in the light-emitting layer, and the lower the oscillation threshold current density, but the higher the threshold voltage.

Further, as shown in Examples 1, 5 to 9, and Comparative Examples 7 and 8, the thickness ratio T1/T2 between the first waveguide layer and the second waveguide layer is 0.3 to 0.3. 7 or less, when the thickness T1 of the first waveguide layer and the thickness T2 of the second waveguide layer are large, the resistance tends to deteriorate and the threshold voltage tends to increase, but the optical confinement effect is strong and the oscillation threshold current Density decreased.

As shown in Examples 1 and 22, when the average Al composition a' of the clad layer of the first conductivity type is smaller than the average Al composition d' of the clad layer of the second conductivity type, the average Al composition a' and the average Al The oscillation threshold current density was lower than in the case of the same composition d'. Therefore, it is preferable that the average Al composition a' of the clad layer of the first conductivity type is smaller than the average Al composition d' of the clad layer of the second conductivity type.
As shown in Examples 1 and 18 to 21, the oscillation threshold current density decreases as the film thickness of the second-conductivity-type clad layer increases from 300 nm, but the oscillation threshold current density decreases within the film thickness range of 400 to 450 nm. The densities were almost the same. On the other hand, when the thickness of the second-conductivity-type cladding layer is 450 nm, the threshold voltage tends to be higher than when the thickness is 400 nm. From the above, it is preferable that the film thickness of the second-conductivity-type clad layer is 300 nm or more and 400 nm or less.

As shown in Examples 1 and 14 and 15, the larger the number of quantum wells, the lower the oscillation threshold current density. Also, the larger the number of quantum wells, the lower the threshold voltage. From the above, it is preferable that the light-emitting layer has a multiple quantum well structure.
Moreover, as shown in Example 1 and Examples 16 and 17, even if the number of quantum wells was the same, the larger the thickness of the quantum well layer, the lower the oscillation threshold current density.

As described above, in the laser diode of the present disclosure, the Al composition of the first conductivity type cladding layer, the first waveguide layer, and the second waveguide layer, the film thickness T1 of the first waveguide layer, and the second waveguide layer By adjusting the film thickness ratio T1/T2 of the film thickness T2, the oscillation threshold current density can be lowered to enable stable continuous oscillation by pulse driving.

Although the embodiments of the present disclosure have been described above, the above embodiments illustrate devices and methods for embodying the technical ideas of the present disclosure. It does not specify the material, shape, structure, arrangement, etc. Various modifications can be made to the technical idea of the present disclosure within the technical scope defined by the claims.

1 laser diode 10 semiconductor lamination portion 11 substrate 12 first electrode 13 second electrode 101 first conductivity type clad layer 102 first waveguide layer 103 light emitting layer 104 second waveguide layer 105 second conductivity type clad layer 106 contact layer

Claims

a nitride semiconductor substrate containing Al;
a semiconductor lamination portion arranged on the nitride semiconductor substrate;
with
The semiconductor lamination part is
a first conductivity type clad layer disposed on the nitride semiconductor substrate and including a first conductivity type nitride semiconductor layer;
a first waveguide layer disposed on the first conductivity type cladding layer;
a light emitting layer disposed on the first waveguide layer and formed of a nitride semiconductor including one or more quantum wells;
a second waveguide layer disposed on the light emitting layer;
a second conductivity type clad layer disposed on the second waveguide layer and including a second conductivity type nitride semiconductor layer;
has
The first conductivity type cladding layer is Al a Ga (1-a) N (0.7<a<0.8),
The first waveguide layer is Al c1 Ga (1-c1) N (0.6<c1<0.7),
the second waveguide layer is Al c2 Ga (1-c2) N (0.6<c2<0.7);
A laser diode, wherein a film thickness ratio T1/T2 between a film thickness T1 of the first waveguide layer and a film thickness T2 of the second waveguide layer is 0.3 or more and 0.7 or less.
A film thickness T1 of the first waveguide layer is 20 nm or more and 50 nm or less,
2. The laser diode according to claim 1, wherein the film thickness T2 of said second waveguide layer is 50 nm or more and 90 nm or less.
3. The laser diode according to claim 1, wherein the first-conductivity-type clad layer has a thickness of 250 nm or more and 600 nm or less.
The second conductivity type cladding layer is Al d Ga (1-d) N (0<d<1),
4. The laser diode according to claim 1, wherein the average Al composition d' is larger than the average Al composition a' of the first conductivity type cladding layer.
5. The laser diode according to any one of claims 1 to 4, wherein the second-conductivity-type clad layer has a thickness of 300 nm or more and 400 nm or less.
The quantum well layer of the light-emitting layer is Al b Ga (1-b) N (0.4<b<0.6), has a thickness of 3 nm or more and 6 nm or less, and has a multilayer structure of two to four layers. 6. A laser diode according to any one of claims 1 to 5, having a quantum well structure.
7. The laser diode according to claim 1, wherein said nitride semiconductor substrate is an AlN single crystal substrate.
a second conductivity type contact layer disposed on the second conductivity type cladding layer and formed of a nitride semiconductor containing GaN;
The second conductivity type cladding layer contains Al e Ga (1−e) N (0.1≦e≦1), and has a composition gradient in which the Al composition e decreases with increasing distance from the nitride semiconductor substrate, a second-conductivity-type vertical conduction layer having a thickness of less than 0.5 μm and a second-conductivity-type lateral conduction layer containing Al f Ga (1−f) N (0<f≦1);
8. A laser diode as claimed in any one of claims 1 to 7.
9. The film thickness ratio T1/T2 between the film thickness T1 of the first waveguide layer and the film thickness T2 of the second waveguide layer is 0.5 or more and 0.6 or less. A laser diode according to any one of the preceding paragraphs.
The film thickness T1 of the first waveguide layer is 30 nm or more and 50 nm or less,
10. The laser diode according to claim 1, wherein the second waveguide layer has a film thickness T2 of 60 nm or more and 80 nm or less.
11. The laser diode according to any one of claims 1 to 10, wherein the first-conductivity-type clad layer has a thickness of 300 nm or more and 500 nm or less.
The second conductivity type cladding layer is Al d Ga (1-d) N (0<d<1),
The average Al composition d' is 0.8 or more and 0.9 or less, and is larger than the average Al composition a'(0.7<a'<0.8) of the clad layer of the first conductivity type. The laser diode according to any one of Claims 1 to 3.