JPH0695498B2 - Impurity doping method for semiconductor materials - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for doping semiconductor materials with impurities.

[Conventional technology]

Impurity doping into a semiconductor is the most important in the process of manufacturing a semiconductor device, and it is impossible to make a device without impurity doping. However, at present, a semiconductor material having a large forbidden band cannot be freely doped into n-type or p-type. For example, in ZnS (zinc sulfide) used in the present invention,
There is no doping method that can obtain a low resistance p-type.

[Problems to be solved by the invention]

As already mentioned, n-type and p-type doping cannot be easily achieved in a semiconductor material having a large forbidden band. This is because the forbidden band energy is larger than the defect formation energy in the matrix induced by the doping. The reason for this is as follows: 1) In doping, the forbidden band was replaced by a self-compensation action. Defects having a charge opposite to that of the dopant (for example, vacancies of a matrix constituent element) are generated. 2) During doping,
Defects with charges opposite to those of the dopant that is substituted in the normal position by auto-compensation (for example, the same dopant has an interstitial site).
It is believed that this is due to the occurrence of defects). Specifically, in the example of ZnS (zinc sulfide) doped with Li treated in the present invention, it is considered that a p-type crystal cannot be formed due to the reason 2). The fact that you cannot dope p-type is p
The fatal drawback of this type of semiconductor device, which is expected to emit light or operate as a laser diode due to the -n junction, is a drawback.

An object of the present invention is to solve the above-mentioned conventional problems and to provide an impurity doping method for a semiconductor material which can easily achieve n-type and p-type doping even with a semiconductor material having a large forbidden band.

[Means for solving problems]

The impurity doping method for a semiconductor material of the present invention is performed by first doping a semiconductor with impurities by thermal diffusion at a high temperature at regular lattice positions and other positions, and then by diffusion using a combination of heat and an electric field, for example, by an automatic compensation function or the like. Only the generated dopant impurities at the interstitial position are diffused and moved to obtain a layer in which only the dopant substituted at the regular position exists.

[Action]

It is well known that when a certain kind of impurity is diffused into a certain kind of semiconductor, the impurity is located at the interstitial position at the same time as replacing the regular position of the mother body. This occurs when the number of impurity atoms trying to diffuse is smaller than that of the host atoms, and Li and GaP (gallium phosphide) in ZnS described in the present invention are used.
Li in, Li in Si and Ge are well known. On the other hand, the penetration position type impurity in the semiconductor has a smaller energy barrier for diffusion than the substitution position type impurity, and easily diffuses by an electric field if ionized. Therefore, if an electric field is applied to a semiconductor containing an intrusion position and a substitutional position impurity at the same temperature, only the intrusion position type impurity having a small diffusion energy barrier diffuses to one electrode, and only the substitutional position impurity is contained. Layers can be formed.

In the impurity diffusion according to the present invention, regardless of the type of the host semiconductor and the type of the impurity atom used, defect levels of opposite signs (for example, a donor level and an acceptor level, etc., which are generated by high temperature thermal diffusion, and this are due to external factors). It is possible if there is a difference in the diffusion energy barrier (including intrinsic and intrinsic defect levels), and not all cases can be covered 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 order of steps for explaining one embodiment of the present invention. FIG. 1 is for explaining step 1 and FIG. 2 is for explaining step 2. In this embodiment, Zn
A method of diffusing Li into S to obtain a P-type crystal will be described.

First, in step 1, about 20 grams of lithium sulfate is dissolved in 100 grams of water to form a lithium sulfate aqueous solution. Z was cut into this solution to a size of 10 mm × 10 mm × 1 mm and etched with a chromium mixed acid solution and an aqueous potassium hydroxide solution (30%, 90 ° C).
The nS bulk crystal 1 is dipped, then taken out and dried at about 110 ° C. At this time, be careful not to mix other impurities. Next, a well-cleaned quartz ampoule 2 was coated with this lithium sulfate aqueous solution and dried, and ZnS bulk crystal 1 and ZnS powder 3 contained to prevent thermal decomposition of this crystal were placed as shown in the arrangement of FIG. After that, the quartz ampoule 2 is connected to a high vacuum exhaust device. The quartz ampoule 2 is evacuated so that the ZnS powder 3 does not rotate, and the quartz ampoule 2 is sealed off when the ultrahigh vacuum of 10 ⁻⁷ Torr or less is reached. Then, the entire quartz ampoule 2 is placed in an electric furnace 4 and heaters 5 and 6 are used.
The ZnS bulk crystal 1 and the ZnS powder 3 are arranged so as to be independently heated. After the above operation, an electric current is passed through 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 is set to 850 ° C and the temperature of the ZnS powder 3 is set to 870 ° C. And held for 5 hours. After the above heat treatment, the quartz ampoule 2 is broken and the ZnS bulk crystal 1 is taken out and etched with a potassium hydroxide aqueous solution (30%, 90 ° C.), and then tungsten metal is vapor-deposited on both surfaces of the crystal. A 1 mm wire of platinum wire is pressure bonded to the tungsten metal.

Next, in step 2, as shown in FIG. 2, a ZnS bulk crystal having tungsten metal electrodes 8 and 9 on both surfaces of the crystal, to which a voltage has been applied, was previously diffused with Li in a well-cleaned quartz ampoule 7. 10 and ZnS powder 11 put in to prevent thermal decomposition of this crystal are arranged, and platinum wires 12 and 13 drawn out from the tungsten metal electrodes 8 and 9 are
Through electrodes 14 and 15 that are attached to the quartz ampoule 7 in advance
In addition, the through electrodes 14 and 15 are connected to a power source 16 placed outside the quartz ampoule 7, and the entire quartz ampoule 7 is placed in an electric furnace 17 by independent heaters 18 and 19 for ZnS bulk crystal, respectively. 10 and ZnS powder 11 are arranged so as to be independently heated. After the above operation, electric current is passed through the heaters 18 and 19. The temperature and time for this Li electric field and thermal diffusion, the voltage of the power supply 16, etc. depend on various conditions, but in the case of the present embodiment, the temperature of the ZnS bulk crystal 10 is 320 ° C., the temperature of the ZnS powder 11 is Was set to 400 ° C., the voltage was set to 1000 V, and it was held for 30 hours.

After that, the quartz ampoule 7 was broken and the ZnS bulk crystal 10 was taken out, and the ZnS after the above operation was measured by Hall measurement at room temperature.
As a result of evaluating the hole concentration of the bulk crystal, the hole coefficient is positive,
That is, it was p-type and the carrier concentration was 1 × 10 ¹⁷ cm ^-3 . In addition, Hall measurement was not possible for the sample subjected to only high temperature thermal diffusion of Li (step 1) because of its high resistance.

In this example, ZnS was selected as the semiconductor and Li was selected as the impurity.However, as described in the section of the action, regardless of the type of the host semiconductor used and the type of the impurity atom, the defect level of the opposite sign generated by the high temperature thermal diffusion does not matter. (For example, donor level and acceptor level, etc., and this includes extrinsic and intrinsic defect levels) It is applicable if there is a difference in the diffusion energy barrier, for example, as a base semiconductor, Si, Ge, InP, G
It may be of any type such as aAs, AlGaN, AlGaP, AlGaInSb, ZnSe, C (diamond), and may be crystalline or amorphous. Further, as the impurity atom, not only an element that becomes a normal donor or acceptor but also a transition metal element or the like can be used, and the kind thereof is not limited.

〔The invention's effect〕

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

The present invention is thus capable of controlling the impurity substitution position in the semiconductor by electric field and thermal diffusion,
It is expected to be used for doping irregular semiconductors into all semiconductors.

[Brief description of drawings]

FIGS. 1 and 2 are principle diagrams shown in order of steps for explaining one embodiment of the present invention. FIG. 1 shows a high thermal diffusion step of Li into ZnS (step 1), and FIG. The electric field to ZnS and a thermal diffusion process (process 2) are 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 supply, 17
… Electric furnace, 18,19… Heating heater.

Claims (1)

[Claims] 1. A step 1 of introducing impurities into a semiconductor material,
Successively applying heat and an electric field to the semiconductor material at the same time to diffuse and move only interstitial impurities to form a layer in which only impurities at regular positions are present. 2. Impurity doping to semiconductor material Method.