JPH0810707B2 - Method for forming pn junction of CdTe - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a PN junction of CdTe, and more particularly to heat treating a P-type, N-type or N-type CdTe wafer in a Cd atmosphere or a Te atmosphere. Therefore, it relates to a method of forming a PN junction of CdTe simply and at low cost. CdTe
The PN junction is used as a light energy conversion element or a γ-ray detection element, and the present invention is useful for manufacturing such an element with high quality and at low cost.

Problems of the Prior Art CdTe PN junctions have been conventionally formed by the following techniques: 1. A method of diffusing impurity atoms serving as donors or acceptors by heat treatment. For example, an example of producing an electroluminescence diode by phosphorus diffusion in N-type CdTe has been reported.

2. A method of depositing an N-type or P-type layer on a P-type or N-type substrate by an epitaxial growth method. For example, there is a reported example in which a PN junction having good photovoltaic properties is formed by causing epitaxial growth of an arsenic or phosphorus-doped CdTe layer on an N-type substrate.

3. A method of forming a PN junction by injecting an atom serving as a donor or an acceptor by an ion injection method. For example, N type
An example of forming a P-type layer by introducing 400 KeVAs ⁺ into CdTe at a dose of 3 × 10 ¹⁵ cm ^-2 has been reported.

In the case of the thermal diffusion method of 1, due to its self-compensation effect, it is difficult to control the electron and hole concentrations by adding impurities,
It is unclear whether or not it acts as an active dopant even if it is doped with a certain kind of impurity, and there is a problem in terms of solid solution limit. In the epitaxial method 2 and the ion implantation method 3, the work process is complicated and the apparatus becomes large, which is a major factor of cost increase.

There is a need in the art for a method of forming a high-quality PN junction that is simpler and cheaper than in the past.

SUMMARY OF THE INVENTION We note the fact that CdTe becomes N-type with Cd excess and P-type with Te excess, and
In addition, we conceived the formation of PN junction by heat treatment in a Te atmosphere and repeated tests, and obtained good results. In this way,
It was possible to easily form the N-type layer or the P-type layer on the surface of the P-type or N-type CdTe wafer without using impurities such as P by controlling the temperature and / or time conditions.

Thus, according to the present invention, the P-type or N-type
A CdTe wafer of the mold and Cd or Te away from the CdTe wafer, the CdTe wafer and the Cd or Te
Is separately heated, and a PN junction is formed on at least one surface of the CdTe wafer by performing a heat treatment in which hydrogen or an inert gas flow is sent from the Cd or Te toward the CdTe wafer, in which case the heat treatment conditions are changed. There is provided a method for forming a PN junction of a CdTe wafer, which is characterized by adjusting the thickness of an N-type layer or a P-type layer formed by the above.

Detailed Description of the Invention A CdTe single crystal is produced by gradually solidifying a melt generated in a high temperature part by relative movement between a crystal growth ampoule containing Cd and Te raw materials and a heating furnace having a predetermined temperature distribution. Has been prepared. The method of moving the crystal growth ampoule is called the Britzmann method. In addition to this, a modified vertical Britzmann method, a THM (Travelling Heater Method) method, and the like have been proposed to suppress the evaporation of Cd that easily evaporates.

The CdTe single crystal can be a P-type or N-type depending on the composition of the raw materials Cd and Te, the addition of a dopant, and the growth conditions such as heat treatment. By cutting such a P-type or N-type CdTe single crystal, a P-type or N-type wafer is obtained.

On one or both sides of such P-type or N-type wafers
Forming a PN junction is the subject of the present invention. That is, P
By forming an N-type layer on one side of a CdTe-type wafer
This results in the formation of junctions, the formation of NPN structures by forming N layers on both sides of a P-type CdTe wafer or the formation of NP or PNP structures by the use of N-type CdTe wafers. These are collectively referred to as PN junction formation in the present invention.

According to the present invention, a P-type or N-type CdTe wafer is heat treated in a reaction tube in a Cd atmosphere or a Te atmosphere. Referring to FIG. 1, a boat 3 for mounting a CdTe wafer 2 is placed on a part of a reaction tube 1 such as a quartz tube. A port 4 containing Cd or Te is placed away from it. An inert gas stream such as hydrogen or argon can be sent into the reaction tube. As an operation example, a CdTe wafer is heated to 500 to 900 ° C. in a stream of hydrogen gas at atmospheric pressure, and Cd and Te are heated to 400 to 800 ° C. P type Cd
Cd is used for Te wafers and Te is used for N-type CdTe wafers.

The thickness of the N-type layer or P-type layer formed on the surface of the CdTe wafer can be freely adjusted by changing the temperature of the CdTe wafer and / or the conditions of the heat treatment.

When forming an N-type layer on a P-type CdTe wafer, it is possible to form a layer having a thickness of 20 to 80 μm in 1 to 5 hours. However, when forming a P-type layer on an N-type CdTe wafer, Te
Since the diffusion constant of CdTe in CdTe is small, it requires much longer processing time.

When a P-type or N-type layer is formed on only one side of a CdTe wafer, the surface on the side not formed is masked by an appropriate means such as resist coating. Alternatively, the masking effect can be easily obtained by devising the way of loading the CdTe wafer on the boat so that the Cd or Te gas does not hit the boat. For example, the wafer may be placed horizontally on the boat with the surface to be masked facing down, or the wafers may be placed in pairs on the boat with the surfaces to be masked facing each other.

EFFECTS OF THE INVENTION 1. Since the formation of the PN junction of the CdTe wafer is brought about by Cd or Te, there is no adverse effect of using impurities such as In and P.

2. The thickness of the P-type layer or N-type layer can be freely controlled simply by changing the heat treatment conditions.

3. The operation is simple and does not require complicated and large equipment.

4. The cost is low.

Thus, the present invention can be used as an effective means for manufacturing a PN type CdTe device.

Example A P-type CdTe wafer was heated in a quartz reaction tube at 800 ° C. in a 0.5 atm Cd atmosphere to form an N-type layer on both sides. FIG. 2 shows the results of examining the change in the thickness of the N-type layer formed by changing the heat treatment time.

Next, a change in the thickness of the N-type layer was examined by changing the heat treatment temperature while keeping the heat treatment time constant for 3 hours. Results are shown in FIG.

As described above, according to the present invention, the thickness of the P-type layer or the N-type layer can be adjusted by changing the heat treatment temperature and / or the heat treatment time.

[Brief description of drawings]

FIG. 1 is a schematic diagram of the method of the present invention, FIG. 2 is a graph showing the relationship between heat treatment time and N-type layer thickness, and FIG. 3 shows the relationship between heat treatment temperature and N-type layer thickness. It is a graph shown. 1: Reactor tube 2: CdTe wafer 3: Boat 4: Cd or Te storage boat

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Claims (1)

[Claims] 1. A Pd or N type CdTe wafer is placed in a part of a reaction tube and Cd or Te is placed away from the CdTe wafer, and the CdTe wafer and the Cd or Te are separately heated to remove hydrogen or hydrogen. Inert gas flow from the Cd or Te
CdTe wafers are heat-treated by sending them to
A method for forming a PN junction on a CdTe wafer, which comprises forming a PN junction on at least one surface of a CdTe wafer and adjusting the thickness of an N-type layer or a P-type layer formed by changing heat treatment conditions.