JPH1140890A - Low-resistance gallium nitride light-emitting device and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the contact resistance between a gallium nitride semiconductor and an electrode by a method, wherein a first layer which forms the electrode coming into contact with the semiconductor is formed of indium. SOLUTION: An n electrode 213s first layer coming into contact with a gallium nitride contact layer 111 is formed of indium, so as to lessen a contact resistance between the n electrode 213 and the contact layer 111. The n electrode 213 is composed of an indium layer (first layer), a titanium layer (second layer), and an aluminum layer (third layer). In such a structure, when the electrode and the contact layer are alloyed, gallium nitride contained in the contact layer and indium contained in the first layer of the n electrode are alloy into Inx Ga1-x N (0<X<1). A forbidden band energy of Inx Ga1-x N is smaller than that of gallium nitride, so that an interface Schottky barrier between the contact layer and the metal electrode becomes low. Therefore, the electrode can be reduced in contact resistance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting device including at least one layer of gallium nitride, indium nitride, aluminum nitride, or a mixed crystal thereof (hereinafter, simply referred to as a gallium nitride light emitting device). The present invention relates to a gallium nitride-based light emitting device having a low density and a method for manufacturing the same.

[0003]

2. Description of the Related Art Gallium nitride is compared with conventional general compound semiconductors such as indium phosphide and gallium arsenide.
Large forbidden energy. Therefore, gallium nitride-based compound semiconductors are expected to be applied to light-emitting devices (semiconductor lasers (hereinafter simply referred to as lasers) and light-emitting diodes) from green to ultraviolet.

Heretofore, generally, p-type gallium nitride and n-type gallium nitride have been used as contact layers for a p-electrode and an n-electrode of a gallium nitride-based light emitting device by current injection. FIG. 4 is a schematic cross-sectional view of a typical gallium nitride-based laser according to the related art (S.
Nakamura et al., Jpn. J. Appl. Phys. 35 (1996) L7
Four). This gallium nitride-based laser comprises an undoped gallium nitride low-temperature growth buffer layer 102 having a thickness of 300 A (angstrom) on a sapphire substrate 101 having a (0001) plane as a surface, and a 3 μm-thick n-type nitride doped with silicon. A gallium contact layer 203, a 0.1 μm thick n-type In _0.1 Ga _0.9 N layer 104 doped with silicon, a 0.4 μm thick n-type Al _0.15 Ga _0.85 N clad layer 105 doped with silicon, Added 0.1 μm thick n-type gallium nitride optical guide layer 106, 25 A (angstrom) undoped In _0.2 Ga _0.8 N quantum well layer and 50 μm thick
A (Angstrom) undoped In _0.05 Ga _0.95 N
26-period active layer 10 having a multiple quantum well structure comprising a barrier layer
7. Magnesium-added p-type Al _0.2 Ga _0.8 N layer 108 having a thickness of 200 A (angstrom), magnesium-added p-type gallium nitride optical guide layer 109 having a thickness of 0.1 μm, and magnesium-added thickness 0.4μm
P-type Al _0.15 Ga _0.85 N cladding layer 110, magnesium-added 0.5 μm-thick p-type gallium nitride contact layer 111, nickel (first layer) and gold (second layer)
And an n-electrode 113 made of titanium (first layer) and aluminum (second layer).

[0005]

In such a conventional gallium nitride-based laser, the gallium nitride used as a contact layer for the electrode has a large bandgap energy of 3.4 eV, so that the contact between the electrode and the gallium nitride cannot be reduced. There was a problem that resistance was high. For example, although the contact resistance of the n-electrode is relatively low at about 8 × 10 ⁻⁶ Ω · cm ² (ME Lin et
al., Appl. Phys. Lett. 64 (1994) p. 1003), further suppression of heat generation of the light emitting element is expected.

A typical p-type dopant in a gallium nitride-based compound semiconductor is magnesium,
Generally, magnesium is inactive immediately after the gallium nitride layer to which magnesium is added by crystal growth. Although magnesium can be activated to some extent by subsequent annealing using heat or an electron beam, the activation rate is not so high, and it has been difficult to increase the p-type carrier concentration to a certain degree or more. Therefore, the contact resistance of the p-electrode was particularly large, about 6 × 10 ⁻² Ω · cm ² (Kobayashi et al., Proceedings of the 56th JSAP Autumn Meeting, 20a-V, 1995) -1).

An object of the present invention is to reduce the contact resistance between a gallium nitride-based semiconductor and an electrode, thereby realizing a gallium nitride-based light-emitting device having a low electrode contact resistance.

[0008]

The gallium nitride-based light-emitting device of the present invention comprises an n-electrode in a gallium nitride-based light-emitting device including at least one layer of gallium nitride, indium nitride, aluminum nitride, or a mixed crystal thereof. Indium is used as the first layer in contact with the semiconductor. The n-electrode is formed of indium (first
Layer) and titanium (second layer) and aluminum (third layer).
Layer).

Further, the method of manufacturing a gallium nitride-based light emitting device of the present invention is a method of manufacturing a gallium nitride based light emitting device including at least one layer of gallium nitride, indium nitride, aluminum nitride or a mixed crystal thereof.
An n-electrode using indium is formed as a first layer in contact with a semiconductor on a contact layer, and In _x Ga ₁ -xN (0 <x <1) is formed in the contact layer by an alloy.

Further, the gallium nitride based light emitting device of the present invention is a gallium nitride based light emitting device of the present invention, wherein the gallium nitride based light emitting device includes at least one layer of gallium nitride, indium nitride, aluminum nitride or a mixed crystal thereof. Further, as the contact layer for the electrode, GaNAs having a smaller forbidden band energy than gallium nitride is used. Further, the gallium nitride-based light-emitting element of the present invention is a gallium nitride-based light-emitting element including at least one layer of gallium nitride, indium nitride, aluminum nitride, or a mixed crystal thereof. Characterized by using GaN _1-x As _x (0.2 ≦ x ≦ 0.8) in which is less than or equal to zero.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described in detail based on embodiments with reference to the drawings.

Example 1 In Example 1, indium was employed as the first layer of the n-electrode in contact with the contact layer in order to reduce the contact resistance between the n-electrode and the gallium nitride-based contact layer.

FIG. 1 is a schematic cross-sectional view of the gallium nitride based laser thus formed. In FIG. 1, a gallium nitride based laser has a 300 A (angstrom) undoped gallium nitride low temperature growth buffer layer 1 on a sapphire substrate 101 having a (0001) plane as a surface.
02, a silicon-added n-type gallium nitride contact layer 203 having a thickness of 3 μm, a silicon-added thickness of 0.1 μm
N-type In _0.1 Ga _0.9 N layer 104, thickness of 0.4 μm to which silicon is added
m, n-type Al _0.15 Ga _0.85 N cladding layer 105, n-type gallium nitride optical guide layer 1 with a thickness of 0.1 μm doped with silicon
06, 25A (angstrom) undoped
26 comprising an In _0.2 Ga _0.8 N quantum well layer and an undoped In _0.05 Ga _0.95 N barrier layer having a thickness of 50 A (angstrom).
Periodic multiple quantum well structure active layer 107, p-type Al with a thickness of 200A (angstrom) doped with magnesium
_0.2 Ga _0.8 N layer 108, p-type gallium nitride optical guide layer 109 with a thickness of 0.1 μm doped with magnesium, p-type Al _0.15 Ga with a thickness of 0.4 μm doped with magnesium
_0.85 N cladding layer 110, p-type gallium nitride contact layer 111 with a thickness of 0.5 μm doped with magnesium,
P electrode 112 made of nickel (first layer) and gold (second layer), indium (first layer) and titanium (second layer)
And an n-electrode 213 made of aluminum (third layer).

In the gallium nitride based laser of this embodiment, indium is used as the first layer of the n-electrode in contact with the contact layer, and when the electrode and the contact layer are alloyed, the contact layer with the n-electrode is nitrided. Gallium and indium in the first layer of the n-electrode are alloyed to form In _x Ga _1-x N (0 <x
<1) occurs. Since the forbidden band energy of In _x Ga _1-x N (0 <x <1) is smaller than the forbidden band energy of gallium nitride, the gallium nitride-based laser of this embodiment has a higher contact energy than the conventional gallium nitride-based laser. The Schottky barrier at the interface between the layer and the metal electrode is reduced. Therefore, when the carrier concentration of the contact layer with respect to the n-electrode is about the same, the gallium nitride-based laser of this embodiment has a lower contact resistance of the electrode than the conventional gallium nitride-based laser. That is, the gallium nitride-based laser of the present embodiment can have a smaller oscillation threshold current and a lower oscillation threshold voltage than the conventional gallium nitride-based laser.

In this embodiment, an example of indium (first layer), titanium (second layer) and aluminum (third layer) has been described as an n-electrode, but the present invention is not limited to this.
The electrode in contact with the contact layer only needs to contain indium.

In the gallium nitride-based laser of this embodiment, In _x Ga ₁ -xN (0 <x <1) generated when the electrode and the contact layer are alloyed tends to be n-type. . Therefore, it is inappropriate to use indium as the first layer of the p-electrode.

Embodiment 2 In Embodiment 2, in order to reduce the contact resistance between the p and n electrodes and the gallium nitride-based contact layer, the contact layers for the p and n electrodes are
GaN _0.1 As _0.9 was adopted.

FIG. 2 is a schematic cross-sectional view of the gallium nitride based laser thus formed. In FIG. 2, a 300 g (angstrom) thick undoped gallium nitride low-temperature growth buffer layer 1 is formed on a sapphire substrate 101 having a (0001) plane as a surface.
02, 3 μm thick n-type GaN _0.1 As _0.9 doped with silicon
Contact layer 303, thickness 0.1 μm to which silicon is added
N-type In _0.1 Ga _0.9 N layer 104, an n-type Al _0.15 Ga _0.85 N cladding layer 105 having a thickness of 0.4 μm doped with silicon, and an n-type gallium nitride optical guide having a thickness of 0.1 μm doped with silicon. A layer 106, a 26-period multi-quantum well structure active layer 107 composed of an undoped In _0.2 Ga _0.8 N quantum well layer having a thickness of 25 A (angstrom) and an undoped In _0.05 Ga _0.95 N barrier layer having a thickness of 50 A (angstrom); 200A (angstrom) with magnesium added
P-type Al _0.2 Ga _0.8 N layer 108, p-type gallium nitride optical guide layer 10 with a thickness of 0.1 μm doped with magnesium
9. 0.4μm thick pAl with magnesium added
_0.15 Ga _0.85 N cladding layer 110, p-type GaN _0.1 As _0.9 contact layer 3 with a thickness of 0.5 μm doped with magnesium
11, a p-electrode 112 made of nickel (first layer) and gold (second layer), and an n-electrode 113 made of titanium (first layer) and aluminum (second layer) are formed.

In the gallium nitride based laser of this embodiment, p
GaN _0.1 As as contact layer for electrode and n-electrode
_0.9 is used. GaN _1-x As _x (0 <x ≦ 1) because the bandgap energy is smaller than that of gallium nitride (Kondo et al., Applied Physics Vol. 65, No. 2 (1996) p. 14
8) The gallium nitride-based laser of this embodiment has a lower Schottky barrier at the interface between the contact layer and the metal electrode than the conventional gallium nitride-based laser. Therefore, when the carrier concentration of the contact layer with respect to the p-electrode and the n-electrode is about the same, the gallium nitride-based laser of the present embodiment has a lower electrode contact resistance than the conventional gallium nitride-based laser. That is, the gallium nitride-based laser of the present embodiment can have a smaller oscillation threshold current and a lower oscillation threshold voltage than the conventional gallium nitride-based laser.

Embodiment 3 In Embodiment 2, in order to reduce the contact resistance between the p and n electrodes and the gallium nitride-based contact layer, GaN _0.5 As _{0.5 is used} as the contact layer for the p and n electrodes of the gallium nitride-based laser. It was adopted.

FIG. 3 is a schematic cross-sectional view of the gallium nitride based laser thus formed. In FIG. 3, a gallium nitride based laser has a 300 A (angstrom) thick undoped gallium nitride low temperature growth buffer layer 1 on a sapphire substrate 101 having a (0001) plane as a surface.
02, the thickness of 0.1μm of N-type GaN _0.5 As _0.5 contact layer 403 having a thickness of 3μm which silicon is added, the silicon was added n-type In
_0.1 Ga _0.9 N layer 104, 0.4 μm thick with silicon added
N-type Al _0.15 Ga _0.85 N clad layer 105, n-type gallium nitride optical guide layer 10 with a thickness of 0.1 μm doped with silicon
6. Undoped In of thickness 25A (angstrom)
26 comprising a _0.2 Ga _0.8 N quantum well layer and an undoped In _0.05 Ga _0.95 N barrier layer having a thickness of 50 A (angstrom).
Periodic multiple quantum well structure active layer 107, p-type Al with a thickness of 200A (angstrom) doped with magnesium
_0.2 Ga _0.8 N layer 108, p-type gallium nitride optical guide layer 109 with a thickness of 0.1 μm doped with magnesium, p-type Al _0.15 Ga with a thickness of 0.4 μm doped with magnesium
_0.85 N cladding layer 110, a thickness of 0.5μm magnesium was added p-type GaN _0.5 As _0.5 contact layer 411,
P-electrode 112 made of nickel (first layer) and gold (second layer); titanium (first layer) and aluminum (second layer)
Layer) is formed.

In the gallium nitride based laser of this embodiment, p
GaN _0.5 As as contact layer for electrode and n-electrode
_0.5 is used. The forbidden band energy of GaN _1-x As _x (0 <x ≦ 1) is smaller than the forbidden band energy of gallium nitride, and especially when about 0.2 ≦ x ≦ 0.8, the bandgap energy becomes a negative metalloid (Kondo et al. , Applied Physics Vol. 65, No. 2
(1996) p. 148), the gallium nitride-based laser of this embodiment does not have a Schottky barrier at the interface between the contact layer and the metal electrode, unlike the gallium nitride-based laser according to the prior art.
Therefore, when the carrier concentration of the contact layer with respect to the p-electrode and the n-electrode is substantially the same, the contact resistance of the electrode of the gallium nitride-based laser of this embodiment is extremely smaller than that of the conventional gallium nitride-based laser. That is, the gallium nitride-based laser of this embodiment has a smaller oscillation threshold current and a lower oscillation threshold voltage than the conventional gallium nitride-based laser.

The present invention is not only effective for the gallium nitride based laser having the structure shown in the above embodiment, but is also effective for gallium nitride based lasers having any layer structure. Note that the present invention does not need to be applied to both the p-electrode side and the n-electrode side, and it is sufficiently effective if applied to only one of the electrodes. Also, the present invention is not only effective in gallium nitride based lasers,
Gallium nitride based light emitting diodes are also effective in reducing the contact resistance of the electrodes.

The semiconductor layer (except for the contact layers of Examples 2 and 3) in each of the embodiments is not limited to this, and can be appropriately selected from gallium nitride, indium nitride, aluminum nitride, or a mixed crystal thereof. Needless to say,

[0025]

As described above, according to the present invention, by employing a novel material for the electrode of the gallium nitride-based light emitting device or the contact layer for the electrode, the electrode which has become a problem in the gallium nitride based light emitting device. This has the effect that the contact resistance can be reduced. For example, in the case of a gallium nitride-based laser, the oscillation threshold current and the oscillation threshold voltage can be reduced. In the case of a light emitting diode, the operating current and operating voltage for obtaining the required light output can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a gallium nitride-based laser employing indium as a first layer of p and n electrodes in Example 1.

FIG. 2 is a schematic sectional view of a gallium nitride based laser employing GaN _0.1 As _0.9 as a contact layer for p and n electrodes in Example 2.

FIG. 3 is a schematic sectional view of a gallium nitride based laser employing GaN _0.5 As _0.5 as a contact layer for p and n electrodes in Example 3.

FIG. 4 is a schematic cross-sectional view of a typical gallium nitride based laser employing gallium nitride as a contact layer for p and n electrodes according to the prior art.

[Explanation of symbols]

Reference Signs List 101 sapphire substrate 102 low-temperature growth buffer layer of gallium nitride 104 n-type In _0.1 Ga _0.9 N layer 105 n-type Al _0.15 Ga _0.85 N layer 106 n-type gallium nitride optical guide layer 107 In _0.2 Ga _0.8 N / In _0.05 Ga _0.95 N multiple quantum Well active layer 108 p-type Al _0.2 Ga _0.8 N layer 109 p-type gallium nitride optical guide layer 110 p-type Al _0.15 Ga _0.85 N cladding layer 111 p-type gallium nitride contact layer 112 p electrode made of nickel and gold 113 made of titanium and aluminum N electrode 203 n-type gallium nitride contact layer 212 p made of indium, nickel and gold
Electrode 213 n-electrode made of titanium and aluminum 303 n-type GaN _0.1 As _0.9 contact layer 311 p-type GaN _0.1 As _0.9 contact layer 403 n-type GaN _0.5 As _0.5 contact layer 411 p-type GaN _0.5 As _0.5 contact layer

Claims (5)

[Claims] At least one layer of gallium nitride, indium nitride, aluminum nitride or a mixed crystal thereof is provided.
A gallium nitride-based light-emitting device comprising a single layer, wherein indium is used as a first layer constituting an n-electrode and in contact with a semiconductor. 2. The gallium nitride based light emitting device according to claim 1, wherein said n-electrode is made of indium (first layer), titanium (second layer) and aluminum (third layer). . 3. A layer of gallium nitride or indium nitride or aluminum nitride or a mixed crystal thereof at least.
In a method for manufacturing a gallium nitride based light emitting device including one layer,
Forming an n-electrode using indium as a first layer in contact with the semiconductor on the contact layer, and forming In _x Ga ₁ -xN (0 <x <1) in the contact layer by an alloy; A method for manufacturing a gallium-based light emitting device. 4. A gallium nitride-based light emitting device comprising at least one layer of gallium nitride, indium nitride, aluminum nitride or a mixed crystal thereof, wherein the GNAs have a forbidden band energy smaller than that of gallium nitride as a contact layer for the electrode. A gallium nitride-based light-emitting device, comprising: 5. A least one layer comprising a gallium nitride-based light emitting device layers of aluminum indium gallium nitride or nitride or nitride, or mixed crystals thereof, as a contact layer for the electrodes, GaN ₁ forbidden band energy becomes zero or less _A gallium nitride-based light emitting device using _-x As _x (0.2 ≦ x ≦ 0.8).