JPS5911675A - P-side ohmic electrode for compound semiconductor - Google Patents

Abstract

PURPOSE:To obtain the P ohmic electrode, heat resistance thereof is high and which is not exfoliated, by providing multilayered structure in which a first layer is made of Cr or Ti, a second layer of Mo or W and a third layer of Au. CONSTITUTION:An N type InGaAsP layer 34 of a conduction type different from a buried layer 32 consisting of P type InP formed to an N type InP substrate 31 is formed to the surface in order to limitedly flow currents through an InGaAsP active layer 33 buried by the buried layer 32, a clad layer 35 consisting of P type InP and a high conduction layer 36 consisting of P type InGaAsP called a cap layer are formed, and an ohmic contact is easy to be obtained. Ti is applied in 50nm thickness was the first metallic layer 38, Mo on the layer 38 in 150nm thickness as the second metallic layer 39 and Au on the layer 39 in 1mum thickness as the third metallic layer 40. The sum of the film thickness of the first layer 38 and the second layer 39 does not exceed 400nm, and these layers are formed to an element with crystalline thickness of 150mum or less. Accordingly, adhesive property is excellent, cracks are not generated, heat resistance is high, and a diffusion to the electrode side of a semiconductor laser crystal and a diffusion into the crystal of Au or a solder material can be inhibited.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ohmic electrode of a ■-V group compound semiconductor.

In order to increase the reliability of semiconductor lasers, it is necessary to effectively dissipate Joule heat generated mainly within the active layer during operation to the outside. FIG. 1 shows the mounting structure of a semiconductor laser device. The laser chip 11 uses indium (In) and gold-germanium (Au-Qe) as the solder material 12.
For example, copper (CLI), molybdenum (Mo), silicon (Si), silicon carbide) is used as the mount material 13 with high thermal conductivity.
(SiC). Particularly problematic here is the structure in which the active layer 14 of the laser is bonded to the mount material side. Note that 15 is an electrode of the laser chip.

One of the causes of device deterioration is the diffusion of Au or solder material into the active layer.

Since a semiconductor laser uses a cleavage in the optical cavity surface, the crystal thickness of the device needs to be around 100 μm.

If it is thinner than this, the element will deteriorate due to stress applied to the active layer. Also, if it is thick, cleavage becomes difficult, and this upper limit is 1
It is about 50 μm. Ti,
When a hard metal such as Or, Mo, or W is deposited, if the total thickness exceeds 400 nm, cracks may occur in the film. In addition, when a semiconductor laser chip is cleaved, these metal particles are generated, blocking the light from the original emission surface of the device, and causing defects that can short-circuit the 'p-n junction electrically exposed to the cavity surface. Likely to happen.

Cr and 'l'i used for the first layer of the casing are ()aAs.

It is a metal that has good adhesion to compound semiconductors such as In()aAsP, and the adhesion strength is not reduced by heat treatment during the manufacturing process of the electrode forming element. It also has good electrical properties, ie, contact resistance and thermal stability. In order to ensure the properties of this film, a minimum film thickness of 5 Qnm is required to eliminate pinholes, which are significant defects. Normally, up to about 3QQnm is used.

Mo and W in the second layer are provided to prevent the third layer of Au or solder from reacting with Ti during the heat treatment during the device manufacturing process and to prevent Au from diffusing into the crystal. also requires a minimum of 50 nm. Also, generally 3
00 nm is used.

An object of the present invention is to prevent electrode deterioration of m-v group compound semiconductor devices, particularly semiconductor lasers, and surface-emitting light emitting diodes.
The object of the present invention is to provide a p-ohmic electrode that has a multilayer structure of Au layers, has high heat resistance, and does not cause peeling.

Figure 2 shows Ti/M deposited on a GaAs wafer.
The O/All multilayer film was heat treated and the depth distribution of elements before and after the heat treatment was measured. The thickness of each layer is 1
llicυ50 nm, Mo@l 50 nm, A
uG! It is 31 μm. In addition, Au was removed by etching before analysis. Auger electron spectroscopy was used for the measurement. FIG. 2(a) shows the element distribution as deposited, and FIG. 2(b) shows the element distribution after heat treatment at 400c. As is clear from this, the chemical vapor deposition process (360tll'~400C) of SiO or PSG film used in ordinary compound semiconductor processes and the process of AuGe
Even in the alloying heat treatment process (approximately 400 tl') of N, t-mic electrode using Ni etc., Au does not enter the crystal and GaG, which is a crystal constituent element! 41. As
It has become clear that (to) does not diffuse into the electrode. In addition, InP has a Cr/MO/Au multilayer film (Cr5
0nm/M.

200 nm/A u I A m ) was deposited and the sample was subjected to a heat treatment of 400 t:', and one distribution of elements in the depth direction was measured. For comparison, InP has Cr/
A u multilayer film (Crl-00nm/ALIIμm) t=
Comparisons were made with those that were deposited and subjected to the same heat treatment. T
In the i/MO/Au electrode, Au, In, and P are not mutually diffused, but in the Cr/Au electrode, In is diffused on the Au surface, and Au also reacts with the crystal. From this, it became clear that the Mo layer was working effectively.

By the way, when a deposited film is generally thin, metal particles are only distributed in lumps, and the film is not completely continuous. To obtain this continuous film with high melting point metal, 500m'f
, requires a minimum. On the other hand, this high melting point metal is hard and the internal strain accumulated in the deposited film is large, so as the film thickness increases, cracks are more likely to occur. Furthermore, if the wafer is thin, it may peel off from the crystal due to thermal stress or the like after being applied. This is GBAs with a thickness of 100 μm.

When conducting experiments on TnP wafers, it was confirmed that this defect does not occur when the thickness is 400 nm or less.

Hereinafter, an example of the present invention will be explained using InGaAsP shown in FIG.
/I An explanation will be given using an nP semiconductor laser.

In order to limit current flow to the InGaAsp active layer 33 buried by the buried layer 32 made of p-type InP formed on the n-type InP substrate 31, an n-type nQaAsP layer having a conductivity type different from that of the buried layer 32 is formed. 34 is provided on the surface, and a cladding layer 35 made of p-type InP is provided on the InGaAsP active layer 33.
A highly conductive layer 36 made of p-type InGaAsP called a cap layer is provided to facilitate obtaining ohmic contact. Ti is deposited to a thickness of 50 nm as a first metal layer 38, Mo is deposited to a thickness of 150 nm as a second metal layer 39 thereon, and Au is deposited to a thickness of 1 μm as a third metal layer 40 thereon.

At this time, Cr may be used for the first layer and W may be used for the second layer.

Generally, after this, the counter electrode 41 is made of ALIGeNi.
After forming with ohmic material, it is made into chips.

As described above, the semiconductor laser having the electrode of the present invention has a
tZ: Stable operation even in 5mW high temperature high power operation life test? There was almost no increase in the operating current even after about 1000 hours. In particular, there was no deterioration due to the reaction between the solder material and the crystal constituent elements or the diffusion of the solder material toward the laser element, unlike in the case of the 1-electrode of Cr/Au only.

Good results were obtained when the present invention was applied to a GaAs-GaAtAs thread double telephoto semiconductor laser.

According to the present invention, the electrode side of the semiconductor laser crystal has good adhesion, no cracks, and high heat resistance. :, A
Since it is possible to provide an electrode that can suppress the diffusion of U or solder material into the crystal, it is effective in preventing electrode deterioration of semiconductor lasers and light emitting diodes.

[Brief explanation of the drawing]

Figure 1 is a perspective view of the semiconductor laser in an unmounted state.
Figure 2 shows data on the heat resistance of the multilayer film of the present invention, and Figure 3 shows an example of InGaAsP using the electrode of the present invention.
FIG. 2 is a perspective view of a /InP semicircular body laser. 11...Semiconductor laser element side, 12...Solder material,
13... Submount, 14... Semiconductor laser active layer 121-T i , 22=-Mo, 24-Ga,
25-As2S3...n-type InP substrate, 32-p-type InP buried layer, 33...InGaAsp active layer, 34...n-type InP (J a As P
layer, 35-p-type np cladding layer, 36-p-type InG
aAsp cap layer, 37- SiO2 insulation film, 38
...1m of first metal consisting of Ti (father is Cr), 39
...Second metal layer made of Mo (or W), 40...
・3rd layer All, 41...n ohmic counterweight 1 Figure 4 Punishment 2 Figure (ku) (-f-9 distance lock (PPrL)
E giant #π 9th row, no'f: J3 diagram dθ Inside the Central Research Laboratory, Hitachi, Ltd., 1-280 Higashi-Koigakubo, Kokubunji-shi Inventor Kuninori Imai Inside the Central Research Laboratory, Hitachi, Ltd., 1-280 Higashi-Koigakubo, Kokubunji-shi Inventor: Hirokato Kato, 111 Nishiyokote-cho, Takasaki City, Hitachi, Ltd., Takasaki Factory, Elderly Inventor: Masamichi Kobayashi, 111 Nishiyokote-cho, Takasaki City, Hitachi, Ltd., Takasaki Factory

Claims (1)

[Claims] For wafers heavily doped with acceptor impurities by diffusion or ion implantation, a titanium (T i ) or chromium (Cr
) as the first layer, tungsten (W) with a film thickness of 5 Qnm or more
Or, for an element in which molybdenum (MO) is used for the second layer and 80 is used for the third layer, and the sum of the film thicknesses of the first and second layers does not exceed 4QQnm, and the crystal thickness is 150μm or less. A compound semiconductor P-side ohmic pole is formed.