JPH11274642A - Semiconductor light emitting device and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve single longitudinal mode control and higher-order transverse mode control in a nitride semiconductor laser, realize high monochromaticity and excellent beam characteristics, and improve reliability. . SOLUTION: An MQW active layer 17 is formed on a sapphire substrate 10 by p-type and n-type AlGaN cladding layers 12 and 20.
In the nitride-based semiconductor laser sandwiched between the layers, a diffraction grating composed of the W light absorbing layer 13 and the SiO ₂ layer 14 is formed in a region between the active layer 17 and the n-type cladding layer 12 on the substrate 10 side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light emitting device using a nitride-based semiconductor material, and more particularly, to GaInAl.
The present invention relates to a nitride semiconductor light emitting device made of a BN material and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, short-wavelength semiconductor lasers have been developed for application to high-density optical disk systems and the like. In this type of laser, it is required to shorten the oscillation wavelength in order to increase the recording density.

InGaAs1 is used as a short wavelength semiconductor laser.
The 600-nm band light source made of a P material has already been put to practical use with its characteristics improved to a level at which both reading and writing of a disk are possible. Blue semiconductor lasers have been actively developed with the aim of further improving the recording density, and oscillations of II-VI group semiconductor lasers have been confirmed. However, there are many barriers to practical use, such as the reliability is limited to about 100 hours, and it is difficult to produce a wavelength of 480 nm or less. There are many.

On the other hand, a GaN-based semiconductor laser has a
m is possible, and the reliability is continuous oscillation at room temperature for several thousand hours or more, and the reliability of LED is confirmed for more than 10,000 hours. I have. As described above, the GaN-based material is an excellent material that satisfies the conditions necessary for the light source of the next-generation optical disk system.

In order to be applicable to next-generation optical disk systems, etc., the conditions for condensing lenses due to color differences become severe due to short wavelengths, so it is important to oscillate in a single longitudinal mode for monochromaticity of the spectrum. However, in nitride-based semiconductor growth requiring high-temperature growth, it has been difficult to preserve a fine diffraction grating.

A GaN-based semiconductor laser is made of AlGaN.
Is used for the cladding layer, but since the GaN layer for the electrode contact outside the A1GaN cladding is transparent to the oscillating light, a so-called anti-guiding phenomenon occurs in which light leaking from the cladding layer is guided. I do. A to avoid this
The lGaN cladding layer may be formed sufficiently thick, but generally, the low-refractive-index layer containing A1 is too thick to grow. For this reason, oscillation is likely to occur in the higher-order vertical transverse mode, which has a lower threshold current than in the fundamental transverse mode, and furthermore, mode competition between adjacent higher-order modes causes kinks in optical output and makes it difficult to focus light with a lens. Then, it was difficult to obtain characteristics that can be used as a light source for an optical disk system.

Further, in the growth of a nitride-based semiconductor layer on a sapphire substrate, high-density dislocations as high as about 10 ⁸ to 10 ¹¹ cm ⁻² are generated, and these dislocations are formed as threading dislocations propagated in the growth direction throughout the crystal. It is present and in the case of a nitride semiconductor laser, penetrates the active layer and reaches the surface of the growth layer.

Therefore, (1) electrical characteristics are poor due to deterioration of current flow and leakage current. (2) At the tip of threading dislocation (point where threading dislocation crosses the growth layer surface), pits are easily generated. (3) Due to disorder in the order of the multiple quantum well structure,
Light emission in the active layer becomes non-uniform. (4) The presence of the pits impairs the surface flatness of the multilayer film for an element such as a semiconductor laser. (5) The electrode material diffuses through a through defect such as a tube-shaped hole when energized. (6) At the time of energization or heat treatment, a dopant such as Mg diffuses through a penetrating defect. There is a problem that the device characteristics and reliability are impaired.

[0009]

As described above, in the conventional nitride semiconductor laser, it is difficult to control a single longitudinal mode, to control a higher-order transverse mode, and to increase the number of crystal defects. Therefore, it is very difficult to obtain good beam characteristics irrespective of the current confinement structure, and the reliability is poor.

The present invention has been made in view of the above circumstances, and has as its object to provide a nitride semiconductor light emitting device having high monochromaticity, excellent beam characteristics, and high reliability, and a method of manufacturing the same. Is to provide.

[0011]

(Structure) The gist of the present invention relates to a structure of a nitride-based semiconductor light-emitting device formed on a substrate such as sapphire, comprising a diffraction grating provided with a light absorption layer, An object of the present invention is to form an active layer which is flat and has few defects such as dislocations by a lateral growth.

That is, the present invention comprises a nitride-based semiconductor,
In a semiconductor light emitting device in which an active layer is sandwiched between cladding layers having different conductivity types, a diffraction grating containing at least a metal is formed between the active layer and the cladding layer or in any region in the cladding layer. And

Further, the present invention provides the method for manufacturing a semiconductor light emitting device, wherein a step of growing a first conductivity type clad layer on the substrate and forming a diffraction grating containing at least a metal on the first conductivity type clad layer are provided. And a step of growing an active layer on the clad layer on which the diffraction grating is formed, and a step of growing a second conductivity type clad layer on the active layer.

Here, preferred embodiments of the present invention include the following. (1) The diffraction grating or the laminated structure is formed on the substrate side with respect to the active layer. (2) The direction of the cavity when forming a semiconductor laser is perpendicular to the [1-100] direction of the nitride semiconductor layer.

(3) Ga _x In _y as a nitride semiconductor
Al _z B _1-xyz N (0 ≦ x, y, z, x + y + z ≦
Use 1). (4) The diffraction grating has a two-layer structure of a metal film and an oxide film or a nitride film. Using SiO ₂ as an oxide film.

(5) The active layer has a multiple quantum well structure (MQ
W). Further, the present invention provides a semiconductor light emitting device including a stacked film including a double hetero junction in which an active layer is sandwiched between cladding layers of different conductivity types, which is formed of a nitride-based semiconductor, and viewed from the cladding layer in the stacked film. A layered structure of oxide or nitride / metal / oxide or nitride is selectively provided at a position opposite to the active layer.

Here, preferred embodiments of the present invention include the following. (1) A stacked structure of oxide or nitride / metal / oxide or nitride, which is formed on the substrate side with respect to the active layer. (2) As a nitride-based semiconductor, Ga _x In _y Al _z B
_{Use 1-xyz} N (0 ≦ x, y, z, x + y + z ≦ 1). (3) SiO ₂ is used as the oxide film.

According to the present invention (claims 1 and 2), in a nitride semiconductor light emitting device (for example, a semiconductor laser) formed on a substrate such as sapphire, an MQW active layer and an underlying A1GaN cladding layer are formed. A diffraction grating is formed in the optical waveguide layer between the layers or in the underlying A1GaN cladding layer, and single longitudinal mode oscillation is performed. This diffraction grating is formed on a metal such as tungsten using a material that can be selectively grown such as SiO ₂ . As a result, not only the longitudinal mode control, but also the light that leaks out of the cladding layer is attenuated by the light absorption effect of the metal, and the higher-order transverse mode has a larger loss or cutoff than the fundamental mode, The far field pattern (FFP) has a single peak, the divergence angle can be suppressed, and the astigmatic difference can be reduced.

When the cavity direction of the semiconductor laser is set to be perpendicular to the [1-100] direction of the nitride semiconductor layer, the stripe direction of the diffraction grating made of metal and SiO ₂ is The crystal growth of the nitride semiconductor of the optical waveguide layer is performed by the metal organic chemical vapor deposition method on this substrate. First, only the exposed nitride semiconductor layer is grown, Lateral growth proceeds on the diffraction grating pattern. In this process, the threading dislocations extend in the vertical direction first, but extend in the lateral direction with the lateral growth, so that the threading dislocations remain in the optical waveguide layer.
Therefore, the dislocation density of the active layer formed on the upper portion can be greatly reduced.

That is, by providing a diffraction grating composed of metal and SiO ₂ , not only single longitudinal mode oscillation is possible, but also the transverse mode is stabilized only in the fundamental mode due to light absorption of the metal layer, and the dislocation density is low. Therefore, it is possible to provide a highly reliable nitride-based semiconductor laser capable of obtaining beam characteristics required for a high-density optical disk system.

According to the present invention (claim 3), in the nitride-based semiconductor light emitting device, an oxide or a nitride / metal / oxide or a nitride is formed on a part of the laminated film including the double hetero junction structure. Is partially created, which is important. This will be described below.

As described above, the conventional GaN-based semiconductor light emitting device has a problem that the light confinement is low and the oscillation threshold is high. Therefore, when an oxide / nitride / metal / oxide / nitride laminated structure is partially formed in a part of the laminated film as in the present invention, light leaking from the cladding layer is reduced to oxide / nitride / metal / It is absorbed by the oxide or nitride layered structure. For this reason, the electromagnetic wave distribution of light spreads around the active layer, and light confinement is greatly improved. Therefore, a semiconductor laser light emitting device having a stable mode and a low oscillation threshold can be obtained.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the illustrated embodiments. (First Embodiment) FIG. 1 is a sectional view showing an element structure of a blue semiconductor laser according to a first embodiment of the present invention.

In the figure, 10 is a sapphire substrate, 11 is n-G
aN contact layer 11 (Si doped: 5 × 10 ¹⁸ c
m ^-3, 3 [mu] m thick), 12 n-A1 _0.08 Ga _0.92 N clad layer ^{(Si-doped: 1 × 10 18 cm -3,} 0.8 thickness
μm), 13 is a W light absorbing layer (50 nm in thickness), 14 is S
iO ₂ layer (thickness 200 nm, width 40 nm, period 80 n)
m), and a diffraction grating is formed from 13 and 14.
Reference numeral 15 denotes an n-GaN optical waveguide layer (Si dope: 1 × 10 ¹⁸ c)
m ⁻³ , thickness 0.3 μm), 16 is n-A1 _0.25 Ga _0.85
N carrier overflow prevention layer (Si doping: 1 × 1
0 ¹⁸ cm ⁻³ , thickness 20 nm), and 17 is a multiple quantum well (M
QW) Active layer. The active layer 17 is made of In _0.15 Ga _0.85
The N well layer (thickness: 3 nm, five layers) and the In _0.02 Ga _0.98 N barrier layer (thickness: 6 nm) are stacked in five layers.

Reference numeral 18 denotes a p-A1 _0.25 Ga _0.85 N carrier overflow prevention layer (Mg dope: 1 × 10 ¹⁸ cm ^-3 ,
20 is a p-GaN optical waveguide layer (Mg doped: 1 × 10 ¹⁸ cm ⁻³ , 0.1 μm in thickness), 20 is p-GaN
A1 _0.08 Ga _0.92 N cladding layer (Mg doped: 1 × 10
¹⁸ cm ⁻³ , thickness 0.8 μm), 21 is a p-GaN contact layer (Mg doped: 2 × 10 ¹⁸ cm ⁻³ , thickness 0.01)
μm), 22 is a p-side electrode made of Pt / Ti / Pt / Au, and 23 is SiO ₂ (thickness 140
nm) is a non-reflective coating film laminated with Although not particularly shown, the n-GaN contact layer 11
An n-side electrode made of A1 / Ti / Au is formed on the partially etched surface.

Next, a method of manufacturing the semiconductor laser will be described. First, from the n-GaN contact layer 11 to the n-A1GaN cladding layer 12 are grown on the sapphire substrate 10 by metal organic chemical vapor deposition (MOCVD). Next, the W light absorbing layer 13 is deposited by using the electron beam evaporation method or the CVD method, and further, the SiO ₂ layer 14 is deposited by the CVD method. Next, a photoresist pattern of a diffraction grating is formed by an interference exposure method so that the resonator direction is perpendicular to the [1-100] direction of the nitride semiconductor layer, and the W light absorbing layer 13 and the SiO ₂ layer are formed by a dry etching method. 14 is partially removed, and the photoresist is further removed.

In this embodiment, the first-order diffraction gratings (13, 14) are formed to facilitate the manufacturing process.
This enabled single longitudinal mode oscillation. Although the period of the diffraction grating may be higher, it is desirable that the thickness of the optical waveguide layer 15 is larger than the width of the diffraction grating mask, whereby the optical waveguide layer 15 having a flat upper surface can be formed.
In addition, it is possible to prevent an increase in electrical resistance due to a decrease in the contact area of the nitride semiconductor in the vertical direction of the diffraction grating.

Next, from the n-GaN optical waveguide layer 15 to the p-GaN contact layer 21 are grown by MOCVD, the n-GaN optical waveguide layer 15 is formed on the diffraction gratings (13, 14) by using lateral growth. By forming a crystal defect, crystal defects such as dislocations are terminated in the surface of the n-GaN optical waveguide layer 15, and the MQW active layer 17 with few threading dislocations was obtained, and the device life was greatly improved. Further, in order to form an n-side electrode, a part of the substrate is etched to the surface of the n-GaN contact layer 11, an n-side electrode is deposited on the surface of the n-GaN contact layer 11, and a p-GaN contact layer is formed. A p-side electrode 22 was deposited on the surface of the layer 21. Furthermore, the resonator length is 0.3 m
m, and a non-reflective coating film 23 was formed on the light emitting end face.

In this embodiment, when the resonator length is 0.3 mm, the threshold current is 75 mA, the oscillation wavelength is 420 nm, a single mode, the operating voltage is 5.0 V, and the continuous oscillation is performed at room temperature.
Furthermore, the device life at 50 ° C. and 5 mW drive is 100
It was over 00 hours. The far field pattern (FFP) had a single peak at a horizontal angle of 8 ° and a vertical angle of 25 °, and the astigmatic difference was as small as 7 μm. Thus, a beam characteristic suitable for optical disk application was obtained.

In the case of the laser of the present embodiment, since the GaN layers 11 and 21 that are transparent to the oscillating light are provided outside the A1GaN cladding layers 12 and 20 sandwiching the MQW active layer 17, the transverse mode is anti-guided. With respect to light that has permeated outside the p-A1GaN cladding layer 20, the p-side electrode 22 can be easily formed because the transparent p-GaN contact layer 21 can be easily thinned.
Can be absorbed. On the n side, since the W light absorbing layer 13 is located immediately above the n-A1GaN clad 12,
The lateral mode distribution is asymmetric with respect to the MQW active layer 17, but the higher-order vertical lateral modes outside the n-A1GaN cladding layer 12 have a large attenuation. Therefore, a single peak FFP
Was obtained, the divergence angle was suppressed, and the astigmatic difference was reduced.

(Second Embodiment) FIG. 2 shows a second embodiment of the present invention.
FIG. 3 is a cross-sectional view illustrating an element structure of a blue semiconductor laser according to the embodiment. The same parts as those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof will be omitted.

This embodiment is different from the first embodiment described above in that the n-A1GaN cladding layer 12 has the same composition as the n-A1GaN cladding layer 12 in the crystal growth on the diffraction gratings (13, 14). The purpose of this is to grow the layer 12a and perform lateral growth of the n-GaN optical waveguide layer 15 where the roof-shaped shape is formed and lateral growth does not start. Therefore, the n-A1 GaN cladding layers 12 and 1
2a has an upper portion forming a diffraction grating.

In this embodiment, when the resonator length is 0.3 mm, the threshold current, oscillation wavelength, operating voltage, element life, F
For the beam characteristics such as FP, almost the same values as in the first embodiment were obtained. Further, the maximum light output is 50 mW, which is about 20% improvement over the first embodiment. In the case of the laser of this embodiment, in addition to the effects of the first embodiment, n-
It is considered that the diffraction efficiency is improved because the upper part of the A1GaN clad is a diffraction grating, and the light output is thereby increased.

As described above, in the first and second embodiments, the case where SiO ₂ is used as the mask material for the diffraction grating and the lateral growth has been described. In addition, 1000 ° C. which is the growth temperature of the nitride semiconductor is used. As long as the material has durability at the above temperature, the same effect can be obtained.
₂ , In ₂ O ₃ , TiN, AlN, SiN, WNx and the like can be used. Further, the metal for light absorption immediately below the diffraction grating may be a metal having a high melting point of about 1200 ° C. or more, and Pt, Ni, Mo or the like may be used in addition to W.

(Third Embodiment) FIG. 3 shows a third embodiment of the present invention.
FIG. 4 is a cross-sectional view showing an element structure of a semiconductor laser according to the embodiment.

In the figure, 31 is a sapphire substrate, 32 is an n-type GaN contact layer, 33 is an n-type AlGaN cladding layer, 34 is an undoped GaN light guide layer, and 35 is In
This is a quantum well active layer made of GaN / InGAN. 3
6 is a p-type GaN optical guide layer, 37 is a p-type AlGaN cladding layer, 38 is a low-resistance p-type GaN contact layer,
Reference numerals 41 and 42 denote n and p electrodes, respectively, which are constricted to a width of 3 μm.

Each of 310, 311 and 312 is made of SiO
₂ , Au, and SiO _2, which are in contact with the substrate 31. The MOCVD method is used for crystal growth. Before growth, SiO ₂ , Au, SiO ₂ is formed on the substrate by sputtering, and thereafter, patterning is performed using a resist such that one width is 2 μm. Dry etching was performed. Thereafter, normal crystal growth was performed. Here, although 310, 311 and 312 are formed directly on the substrate, they may be formed on the nitride-based semiconductor film.

With such a configuration, light leaking from the n-side cladding layer 33 is absorbed by Au 311 in the stacked structure of SiO ₂ / Au / SiO ₂ . For this reason, the electromagnetic wave distribution of light spreads around the active layer 35, and light confinement is greatly improved. Therefore, a semiconductor laser light emitting device having a stable mode and a low oscillation threshold can be obtained. Incidentally, the threshold value of the laser of the structure of this embodiment is 1 k.
A / cm ² , which was 1/5 or less of the conventional value.

In this embodiment, the laminated structure is Si
O ₂ , Au, SiO ₂ was used, but instead of SiO ₂ , oxides such as TiO ₂ , In ₂ O ₃ , TiN, AlN,
It is also possible to use nitrides such as SiN and WNx.
Further, instead of Au, W, Pt, Ni, Mo, or other metals can be used.

In the first to third embodiments,
Although a GaN-based material was used as an element constituent material system, various gallium nitride-based semiconductor materials, specifically, Ga _x
In _y Al _z B _1-xyz N (0 ≦ x, y, z, x + y +
z ≦ 1) can be used. Further, a plurality of elements can be integrated on the same substrate. In addition, various modifications can be made without departing from the scope of the present invention.

[0041]

As described above in detail, according to the present invention, the structure of a nitride-based semiconductor light-emitting device formed on a substrate such as sapphire is provided with a diffraction grating having a light absorbing layer, By forming an active layer that is flat and has few defects such as dislocations by lateral growth, it is possible to realize a nitride-based semiconductor light-emitting device having good beam characteristics and an easy manufacturing method.

Also, by selectively providing an oxide or nitride / metal / oxide or nitride laminated structure in a laminated film including a double hetero junction, light leaking from the cladding layer is absorbed by the laminated structure. As a result, it is possible to realize a mode-stable, low-threshold semiconductor light emitting device having high light confinement, which has not been obtained conventionally.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an element structure of a semiconductor laser according to a first embodiment.

FIG. 2 is a sectional view showing an element structure of a semiconductor laser according to a second embodiment;

FIG. 3 is a sectional view showing an element structure of a semiconductor laser according to a third embodiment.

[Explanation of symbols]

10 ... sapphire substrate 11 ... n-GaN contact layer 12 ... n-A1GaN cladding layer 13 ... W light absorbing layer (diffraction grating) 14 ... SiO ₂ layer (diffraction grating) 15 ... n-GaN optical waveguide layer 16 ... n-A1GaN Carrier overflow prevention layer 17 MQW active layer 18 p-A1GaN carrier overflow prevention layer 19 p-GaN optical waveguide layer 20 p-A1GaN cladding layer 21 p-GaN contact layer 22 p-side electrode 23 anti-reflection coating film

Claims (3)

[Claims] 1. A semiconductor light emitting device comprising a nitride-based semiconductor and having an active layer sandwiched between cladding layers of different conductivity types, wherein at least a metal is provided between the active layer and the cladding layer or in any region in the cladding layer. A semiconductor light emitting device characterized by comprising a diffraction grating comprising: 2. A method for manufacturing a semiconductor light emitting device comprising a nitride semiconductor and having an active layer sandwiched between cladding layers of different conductivity types, comprising: growing a first conductivity type cladding layer on a substrate; Forming a diffraction grating containing at least a metal on the conductive type cladding layer; growing an active layer on the cladding layer on which the diffraction grating is formed;
Growing a conductive cladding layer. 3. A semiconductor light emitting device comprising a laminated film comprising a nitride-based semiconductor and having a double hetero junction structure in which an active layer is sandwiched between cladding layers of different conductivity types, wherein the cladding layer in the laminated film A semiconductor light emitting device characterized by selectively providing a stacked structure of oxide or nitride / metal / oxide or nitride at a position opposite to the active layer when viewed.