JPH027176B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming an electrode on p-type CdTe.

The electrodes formed on the semiconductor surface include non-rectifying (ohmic) electrodes and rectifying (shottky) electrodes.
There are two types of electrodes. Ohmic electrodes are the most important electrodes for measuring the characteristics of semiconductors and making devices, but the combination of electrode materials and semiconductors is difficult.

Conventional methods for forming electrodes include the thermal diffusion method, in which a high concentration of impurities is formed on the semiconductor surface, the electrode is attached, and then heat treated; the alloying method, in which the electrode material and the semiconductor are alloyed at high temperature; and the ion implantation method ( ion implantation), which attaches a different type of semiconductor with good matching to the electrode material,
There is a hetero-epitaxy method as described in No. 2865793. In addition, in the case of semiconductor compounds, a plating method in which constituent elements on the surface of the compound are replaced by electroless plating to form a highly concentrated layer (for example, by applying a gold chloride plating solution to p-type CdTe, There was also a method in which Cd and Au were substituted to form a high concentration layer of Te, forming an Au ohmic electrode.

However, the thermal diffusion method has the drawback that the efficiency of forming the high concentration layer is low because the impurity material forming the high concentration layer is generally easily evaporated. Also,
The alloying method has the disadvantage that electrode materials are limited, and there are few good materials for compound semiconductors, making it difficult to form a good alloy layer. In addition, other methods have the drawbacks of requiring large-scale equipment and increasing the number of steps. In addition, although the Metsuki method is a simple method,
It has poor performance and poor reproducibility.

It is an object of the present invention to eliminate the drawbacks and problems of these conventional methods.

The method according to the present invention is to sequentially apply an Sb (antimony) film and a Ni (nickel) film to the P-type CdTe surface, and then perform heat treatment to form an ohmic junction electrode on the semiconductor surface.

FIG. 1 is a flowchart showing the procedure of an electrode forming method according to the present invention. Here, a case where undoped p-type CdTe is used as the semiconductor will be exemplified.

First, p-type CdTe with no added impurities (manufactured by Yokogawa Electric, resistivity 9.4×10 ² Ω・cm, carrier concentration 1.4
×10 ¹⁵ cm ^-3 ) into 0.8 to 1.4 mm thick wafers,
After polishing and chemically etching the sample with a Br methanol solution, a thin Sb film is first deposited on the sample in vacuum (2 x 10 ^-4 pa) and at room temperature (step 1). Next, a Ni thin film is deposited under the same conditions (step 2).

FIG. 2 is a diagram showing the cross-sectional structure at the time when Step 2 is completed. The Sb and Ni films are approximately 20 and 10 nm thick, respectively.

Subsequently, this was heated in an inert gas (N ₂ , Ar, etc.) at 200°C for 30-60 minutes or at 450°C for 0.5-60 minutes.
Heat treatment for 1 minute (step 3) to complete.

FIG. 3 is a diagram showing the cross-sectional structure at the time when step 3 is completed. Sb and Ni diffuse into CdTe,
A pt high concentration layer 1 is formed between the electrode 2 and CdTe. The device completed in this way is used as an X-ray detector that extracts signals from the electrode 2.

Figure 4 shows that there is a first layer on both surfaces of the P-CdTe crystal.
FIG. 3 is a characteristic diagram showing voltage and current characteristics obtained by forming an Sb/Ni electrode according to the procedure shown in the figure. As is clear from the experimental results, it is recognized that the electrode formed by the method of the present invention is an ohmic junction with good linearity.

FIG. 5 shows the diffusion profile in the depth direction obtained by Auger electron spectroscopy after heat treatment at 450° C. for about 1 minute in step 3. Sb and Ni are
It is observed that it diffuses into CdTe and forms a highly concentrated layer. In FIG. 5, the horizontal axis corresponds to the depth and represents the time it takes for the sample to be ablated with the ions.

As explained above, the method according to the present invention
A two-layer electrode film is formed by covering an impurity (dopant) material that easily re-evaporates and is difficult to diffuse, such as Sb, with a stable metal thin film such as Ni. Ni has the effect of preventing re-evaporation of Sb during heating, and promoting the diffusion of Sb.

Therefore, according to the method of the present invention, it is possible to form an ohmic junction electrode that is mechanically strong, has low electrical resistance, and has good linearity. Also,
The electrode part has a metal film called Ni, so
It is also easy to attach lead wires for signal extraction.

[Brief explanation of drawings]

Fig. 1 is a flowchart showing the steps of the electrode forming method according to the present invention, Figs. 2 and 3 are explanatory diagrams of the cross-sectional structure at the time of completing each step, and Figs. 4 and 5 show the experimental results. FIG. 2 is a characteristic diagram showing an example. 1...p+ high concentration layer, 2... electrode.

Claims (1)

[Claims] 1. Sb film and Ni film are sequentially applied to the surface of p-type CdTe,
An electrode forming method in which an ohmic junction electrode is formed on the surface of the p-type CdTe by subsequent heat treatment. 2. The electrode forming method according to claim 1, wherein the heat treatment is performed at 200°C for 30 to 60 minutes. 3. The electrode forming method according to claim 1, wherein the heat treatment is performed at 450°C for 0.5 to 1 minute.