JPS6390143A - Method of doping impurity into semiconductor material - Google Patents

Abstract

PURPOSE:To realize the manufacture of P-type ZnS by a method wherein, by thermally diffusing a semiconductor at a high temperature, an impurity is intro duced into a regular lattice position and into a position other than that and is diffused by jointly using heat and an electric field so that only a dopant located at an intrusion. type position and produced by an automatic compensa tion effect or the like can be shifted to the regular position. CONSTITUTION:After a ZnS bulk crystal 1 has been immersed in a lithium sulfate aqueous solution, is taken out and dried. This crystal 1 coated with lithium sulfate and a ZnS powder 3 to be used for prevention of pyrolysis of a crystal are put in a clean quartz ampule 2, which is then vacuum-sealed. Then, after the ampule 2 has been put in an electric furnace 4 and has been heated, the ampule 2 is broken and the crystal 1 is taken out. This crystal 10, where W electrodes 8, 9 are attached to its both sides, and a ZnS powder 11 are again put in an ampule 7. The electrodes 8, 9 are connected to an exter nal power source 16 by means of platinum wires 12, 13. After that, the ampule 7 is put in an electric furnace 17 and is heated. At the same time, an electric field is given to the crystal 10 by applying an electric current from the power source 16 in order to control the position where an impurity is rearranged.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention relates to a method of doping semiconductor materials with impurities.

[Conventional technology]

Impurity doping into a semiconductor is the most important process for manufacturing semiconductor devices, and device creation is impossible without impurity doping. However, semiconductor materials with a large forbidden band width cannot be freely doped into n-type or p-type at present.

For example, for Zn5 (zinc liFE) used in the present invention, there is no doping method that allows a low resistance p-type to be obtained.

[Problem that the invention seeks to solve]

As already mentioned, n-type and p-type doping cannot be easily achieved in semiconductor materials with large band gaps. This is because the forbidden band energy becomes larger than the defect generation energy in the host body induced by doping, and the reason for this is: 1) During doping, self-compensation (seH-compensation) causes substitution at normal positions. A defect with a charge opposite to that of the dopant (
2) Auto-compensation occurs during doping.
This is thought to be due to the fact that a defect (for example, a defect in which the same dopant is present at an interstitial position) having a charge opposite to that of the dopant substituted at the normal position is generated due to the dopant substitution at the normal position. Specifically, in the case of ZnS (zinc sulfide) doped with Li, which is treated in the present invention, it is considered that p-type crystals cannot be formed due to the reason 2) above. The impossibility of p-type doping is a fatal drawback in this type of semiconductor device, which is expected to emit light or operate as a laser diode through a p-n junction.

An object of the present invention is to solve the above-mentioned conventional problems and to provide a method for doping impurities into a semiconductor material that can easily achieve n-type and p-type doping even in a semiconductor material with a large forbidden band width.

[Means for solving problems]

The method of doping impurities into semiconductor materials of the present invention involves first doping impurities into regular lattice positions and other positions in the semiconductor by thermal diffusion at high temperatures, and then doping the impurities into the semiconductor by diffusion using both heat and an electric field, such as by an automatic compensation effect. Only the dopant impurity at the generated interstitial position is diffused and moved to obtain a layer in which only the dopant substituted at the normal position exists.

[Effect]

It is well known that when a certain type of impurity is diffused into a certain type of semiconductor, the impurity replaces the normal position of the parent body and at the same time is located at the interstitial position. This often occurs when the impurity atoms attempting to diffuse are smaller than the host atoms, and Li in ZnS, Li in GaP (gallium phosphide), Li in St and Ge, etc. described in this invention are well known. ing. On the other hand, an interstitial impurity in a semiconductor has a smaller energy barrier for diffusion than a substitutional impurity, and if ionized, it can be easily diffused by an electric field. Therefore, if an electric field is applied to a semiconductor containing both interstitial and substitutional impurities at an appropriate temperature, only the interstitial impurities, which have a small diffusion energy barrier, will diffuse to one side of the electrode, and the semiconductor will contain only substitutional impurities. layers can be formed.

In the impurity diffusion according to the present invention, regardless of the type of base semiconductor used or the type of impurity atoms, high-temperature thermal diffusion
It is applicable if there is a difference in the diffusion energy barrier of generated defect levels of opposite sign (e.g., donor level and acceptor level, and this includes extrinsic and intrinsic defect levels). It is not possible to cover all cases here.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings. 1 and 2 are principle diagrams of steps shown in the order of steps to explain an embodiment of the present invention, and FIG. 1 shows step 1. FIG. 2 is for explaining process 2. In this example, Z
A method for obtaining a P-type crystal by diffusing Li into nS will be explained.

First, in step 1, about 20 grams of lithium sulfate is
Dissolve it in gram of water to make a lithium sulfate aqueous solution. In this aqueous solution, cut into 10 x 10 + uXl m pieces, add a chromium mixed acid solution and a potassium hydroxide aqueous solution (30%, 90°C).
The etched ZnS bulk crystal 1 is immersed in the solution, then taken out and dried at about 110°C. At this time, be very careful not to mix other impurities. Next, the ZnS bulk crystal 1, which has been coated with this lithium sulfate aqueous solution and dried, and the ZnS powder 3, which has been added to prevent thermal decomposition of this crystal, are placed in a thoroughly cleaned quartz ampule 2 as shown in Figure 1. After that, connect the quartz ampoule 2 to a high vacuum exhaust system. Z
Evacuate the quartz ampoule 2 so that the nS powder 3 does not spread,
When an ultra-high vacuum of 10-' Torr or less is reached, the quartz ampoule 2 is sealed. Thereafter, the entire quartz ampoule 2 is placed in an electric furnace 4 so that the ZnS bulk crystal 1 and the ZnS powder 3 are heated independently by heaters 5 and 6, respectively. After the above operation, current is applied to the heaters 5 and 6. The temperature and time for this high-temperature thermal diffusion of Li depend on various conditions, but in the case of this example, the temperature of the ZnS bulk crystal 1 was 850°C, and the ZnS powder 3
The temperature was set to 870°C and maintained for 5 hours. After the above heat treatment, the quartz ampoule 2 is broken, the ZnS bulk crystal 1 is taken out, and a potassium hydroxide aqueous solution (30%, 90%
After etching at 30°F (°C), tungsten metal is deposited on both sides of the crystal. A platinum wire of 11III fiber is crimped onto this tungsten metal.

Next, in step 2, as shown in FIG. 2, a ZnS bulk crystal, which has been previously diffused with Li in step 1 and has tungsten metal electrodes 8 and 9 on both sides of the crystal for applying a voltage, is placed in a thoroughly cleaned quartz ampoule 7. 10 and ZnS powder 11 added to prevent thermal decomposition of the crystal, and a platinum wire 12 drawn out from tungsten metal electrodes 8 and 9.
and 13 are connected to the through electrodes 14 and 15 attached to the quartz ampoule 7 in advance, and the through electrodes 14 and 1
5 is connected to a power supply 16 placed outside the quartz ampoule 7, and the entire quartz ampoule 7 is placed in an electric furnace 17 and heated by independent heaters 18 and 19, respectively.
The bulk crystal 10 and the ZnS powder 11 are arranged so as to be heated independently. After the above operation, the heating heater 18
The temperature, time, voltage of the power supply 16, etc. for this Li electric field and thermal diffusion, which cause current to flow through the Li and 19, depend on various conditions, but in the case of this example, the temperature of the ZnS bulk crystal 10 is set at 320°C. The temperature of the Zn, S powder 11 was set to 400°C, the voltage was set to 1000 volts, and the temperature was maintained for 30 hours.

After this, the quartz ampoule 7 is broken, the ZnS bulk crystal 10 is taken out, and the Hall! As a result of evaluating the hole concentration of the ZnS bulk crystal after the above operation, the hole coefficient was positive, that is, p-type, and the carrier concentration was I
It was 1017cs-'.

In addition, Hall measurement was impossible for the sample subjected to only high-temperature thermal diffusion of Li (step 1) due to high resistance.

In this example, ZnS is used as the semiconductor, and L is used as the impurity.
However, as mentioned in the section on effects, regardless of the type of host semiconductor and the type of impurity atoms used, defect levels of opposite sign (for example, donor level and acceptor level) generated by high-temperature thermal diffusion This can also be applied if there is a difference in the diffusion energy barrier of (including extrinsic and intrinsic defect levels); for example, the base semiconductor may be Si, G
e, InP, GaAs, AIGaN, AlGaP, AI
It does not matter whether it is made of GaI nSb, Zn5e, C (diamond), etc., and whether it is crystal or amorphous. Further, the impurity atoms can be not only ordinary elements that serve as donors and acceptors, but also transition metal elements, for example, and are not limited to the types thereof.

〔Effect of the invention〕

As explained above, the electrical characteristics of Li-doped ZnS produced by the method of the present invention show that p-type ZnS, which could not be achieved by conventional methods, can be produced.

In this way, the present invention makes it possible to control the impurity substitution position in a semiconductor by using an electric field and thermal diffusion.
It is expected that it will be used for impurity doping in all semiconductors.

[Brief explanation of the drawing]

1 and 2 are principle diagrams shown in the order of steps to explain an embodiment of the present invention. FIG. 1 shows the high-temperature diffusion process of Li into ZnS (process 1), and FIG. The electric field and thermal diffusion process (step 2) to ZnS is shown. 1...ZnS bulk crystal, 2...quartz ampoule, 3
... ZnS powder, 4... Electric furnace, 5, 6... Heater, 7... Quartz ampoule, 8.9... Tungsten electrode, 10... ZnS bulk crystal, 11...
ZnS powder, 12. ．． 13...Platinum wire, 14.15.
...Through electrode, 16...Power source, 17...Electric furnace, 1
8.19 --- Heating heater.

Claims (1)

[Claims] Impurities into a semiconductor material characterized by comprising a step 1 of introducing an impurity into a semiconductor material, and a step 2 of simultaneously applying heat and an electric field to the semiconductor material to replace the introduced impurity only in desired lattice positions. doping law.