JPH08213653A - Semiconductor device having contact resistance reducing layer - Google Patents

Abstract

PURPOSE: To reduce contact resistance, and remarkably reduce the operating voltage of a light emitting device, by forming a thin film GaPN layer between an AlGeInN based layer and an electrode. CONSTITUTION: In order to reduce contact resistance in wide band gap semiconductor, a thin film GaPxN1-x (0.1<=x<=0.9) layer whose band gap is very small or equal to zero is inserted. Thereby a potential barrier formed between an electrode and a surface layer is remarkably reduced, and ohmic contact is very easily obtained. The values of thickness, composition, etc., of the GaPxN1-x (0.1<=x<=0.9) layer between an AlGaInP based layer and the electrode are different from the carrier concentration and the composition (band gap) of a layer composed of AlGaInP based layer, and therefore not specially limited. Usually the desirable thickness is necessary only for satisfying the effect that the contact resistance is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device, and more particularly to a light emitting element such as a blue to green light emitting diode or a blue to green laser diode using a gallium nitride-based material, and more particularly to a semiconductor device having a greatly reduced contact resistance.

[0002]

2. Description of the Related Art Recent progress in high brightness of blue and green light emitting diodes (LEDs) is remarkable, and ZnSSe-based or AlGaInN-based materials are used as materials. At present, the growth of high quality gallium nitride (GaN) compound semiconductor films on substrates such as sapphire and SiC and the high concentration p-type doping of GaN have enabled the development of high-luminance blue light emitting diodes. It has been realized and uses a double heterostructure as shown in FIG.

[0003]

However, in FIG.
Wide bandgap on the surface contact layer as shown
Of GaN (Eg = 3.39eV)
The potential barrier with the poles tends to increase, which causes
This leads to an increase in pressure (Fig. 3, in the case of n type, E _CIs
Energy at the bottom of the band, E_FIs the Fermi level, E_VIs a charge
Energy of the bottom of the band, qφ_BIs a potential barrier). like this
Wide bandgap semiconductor for lowering contact resistance
First, insert the heavily doped layer directly under the electrode,
In other words, a method to form a structure called metal-n + -n, metal-p + -p
There is a method (Fig. 4, but for n type). This allows
The potential barrier remains, but the depletion layer becomes very thin and carriers
Can freely pass through the tunnel effect, so do not show resistance.
It becomes. In n-type GaN, the hole concentration is 10¹⁹High as a stand
Can be doped to a high concentration, while p-type GaN
In the current situation, 10¹⁷Only enter the level
Yes. For this purpose, especially a layer made of p-type AlGaInN
It is difficult to realize a sufficiently low contact resistance. This operating power
Increased pressure leads to heat generation of the element, which shortens life
Therefore, it becomes a big problem.

[0004]

[Means for Solving the Problems] We use MOCVD and M
In manufacturing an AlGaInN LED by the BE method,
A thin Ga film is formed between the AlGaInN-based layer and the electrode.
By inserting a P _x N _1-x (0.1 ≦ x ≦ 0.9) layer, the above problems have been solved. The reason for this is Ga
PN has the same composition as GaP even if the P composition is increased from GaN.
The reason is that even if the N composition is increased, the band gap decreases, and the band gap becomes zero in the intermediate composition, which is a special band structure. Therefore, in order to reduce the contact resistance with a wide band gap semiconductor,
By inserting a GaP _x N _{1 -x} (0.1 ≦ x ≦ 0.9) layer of a thin film having a very small or zero band gap, even if the carrier concentration cannot be made very high, It is considered that this is because the potential barrier formed between the electrode and the surface layer is significantly reduced, and ohmic contact becomes very easy (FIG. 5, n-type).

From the AlGaInN system, which is the main point of the present invention,
Thin film GaP between the layer and the electrode _xN_1-x(0.1 ≦ x
≦ 0.9) For the layer, the thickness, composition, etc.,
The carrier concentration and composition of the AlGaInN-based layer (Ba
It is not particularly limited because it depends on the band gap),
Usually, the preferable thickness is the effect that the contact resistance decreases.
It only needs to have the thickness necessary to fill the fruit, usually less than 1 μm.
Below, often used in thicknesses of the order of 5-100 nm
Be done.

A more preferable mixed crystal ratio x is 0.1 or more and 0.9 or less, and more preferably 0.2 or more and 0.8 or less.
It is the following. In this specification, the layer made of AlGaInN system includes a layer having a composition of Al or In of 0. Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the examples as long as the gist thereof is not exceeded. (Example) As shown in FIG. 6, the apparatus used for the growth of the present invention has a substrate transfer chamber in the center, one substrate exchange chamber and three decompression MOCVD devices. The growth chamber 1 is an ordinary MOCVD apparatus and is used for growing an AlGaInN-based compound semiconductor. The growth chamber 2 is also an ordinary MOCVD apparatus, but is used for growing III-V group compound semiconductors other than AlGaInN. The growth chamber 3 is capable of radically decomposing the raw material by microwave excitation, and is used for nitriding the substrate surface and growing an AlGaInN-based compound. A procedure for growing an epitaxial wafer having a structure as shown in FIG. 1 will be described.

First, a sapphire substrate is introduced into the growth chamber 3,
Heat up. At 500 ° C., nitrogen gas (N ₂ ) is used as a raw material before growth, radical nitrogen is supplied to the substrate surface by microwave excitation, and oxygen (O) atoms on the surface are replaced with N atoms, that is, nitriding is performed. . A GaN buffer layer 20 nm is grown on this surface. After this,
The substrate is cooled and moved to the growth chamber 1 via the transfer chamber. By heating at a growth temperature of 1000 ° C., an n-type GaN buffer layer 4 μm, an n-type Al _0.2 Ga _0.8 N clad layer 1 μm, and Zn-doped In are formed on the epitaxial film growth substrate.
_0.1 Ga _0.9 N active layer 0.1 μm, p-type Al _0.2 Ga _0.8 N
A clad layer 1 μm and a p-type GaN contact layer 1 μm are sequentially grown. At this time, hydrogen was used as a carrier gas, and trimethylgallium (TM
G), trimethylaluminum (TMA), and trimethylindium (TMI) were used. Ammonia (NH3) is generally used as the group V raw material, but an organic metal such as dimethylhydrazine or ethyl azide, which has good decomposition efficiency at low temperatures, may be used in order to reduce the growth temperature. n
Si or Ge was used as the type dopant, and Mg or Zn was used as the p-type dopant. If necessary, after the growth, heat treatment is subsequently performed in the growth chamber to activate the carriers. After that, the substrate is cooled and moved to the growth chamber 2 via the transfer chamber. The substrate is heated to 700 ° C., and a 20 nm thick GaP film is formed on the epitaxial film growth substrate.
_0.2 N _0.8 is grown as a contact resistance reducing layer. At this time, hydrogen is used as the carrier gas, TMG is used as the group III source gas, NH ₃ and phosphine (P
H ₃₎ was used. The GaP _0.2 N _0.8 contact resistance reduction layer increases absorption of emitted light when it is made too thick. However, as in the above embodiment, contact resistance can be reduced even with a very thin thin film that is not affected by light absorption. It is very effective. Further, the contact resistance reducing layer has a very small resistivity, and therefore plays a role of spreading the current on the surface.

Electrodes were formed on the surface side of the epitaxial wafer thus grown and processed into chips. When this chip was assembled as a light emitting diode to emit light, a light emission wavelength of 420n at a forward current of 20 mA.
m, and the emission output was 800 μW, which were very good values.
At this time, the operating voltage was 3.3 V, and the operating voltage was 4.0 V in the conventional light emitting diode having electrodes formed on the p-GaN surface prepared for comparison. This reduction in operating voltage means reduction in heat generation of the element itself, and the life of the element could be greatly improved.

Although the above-mentioned embodiment is for the light emitting diode, it goes without saying that the semiconductor laser has the same effect, and for all other semiconductor elements in which electrodes are directly provided on the AlGaInN based semiconductor layer,
The loss due to the reduction of resistance can be reduced, and the effect is demonstrated.

[0010]

By inserting a thin GaP _x N _{1 -x} (0.1 ≦ x ≦ 0.9) layer between the AlGaInN-based layer and the electrode, the resistance is reduced and the light is emitted. When used as a device, the operating voltage can be greatly reduced, and the characteristics of the ultraviolet to red AlGaInN-based light emitting device and the device life can be greatly improved.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an example of a semiconductor device of the present invention.

FIG. 2 is an explanatory diagram showing an example of a conventional semiconductor device.

FIG. 3 is an explanatory diagram of an energy band in the case where an electrode is directly placed on a conventional AlGaInN-based semiconductor layer.

FIG. 4 is an explanatory diagram of an energy band when a heavy doped layer is provided on a conventional AlGaInN-based semiconductor layer and an electrode is provided thereon.

FIG. 5 is an explanation of an energy band when an electrode is provided by inserting a GaP _x N _1-x (0.1 ≦ x ≦ 0.9) layer on the AlGaInN-based semiconductor layer of the present invention. It is a figure.

FIG. 6 is an explanatory diagram of a manufacturing apparatus used in Example 1.

Claims (2)

[Claims] 1. A semiconductor device comprising a thin GaP _x N _1-x (0.1 ≦ x ≦ 0.9) layer between an AlGaInN-based layer and an electrode. 2. The semiconductor device according to claim 1, wherein the AlGaInN-based layer is p-type.