JPH0656597A - Production of group ii-vi compound semiconductor single crystal - Google Patents

Abstract

PURPOSE:To provide the semiconductor single crystal which has low resistance and high carrier concn. and exhibits a good electrical conductivity by melting the polycrystalline body of a ZeSe compd. semiconductor which is a main raw material and a Zn simple substance and Ga simple substance which are auxiliary raw materials in a crucible and recrystallizing the melt. CONSTITUTION:The polycrystalline group II-VI compd. semiconductor as the main raw material and the impurity to determine the electrical conduction type of this semiconductor and group II element as the auxiliary raw materials are first electrical conduction type of this semiconductor and auxiliary raw materials are then melted in the crucible. This melt is recrystallized to form the group II-VI compd. semiconductor single crystal exhibiting the electrical conduction type, by which the desired single crystal is obtd. Since the carrier impurity is taken into the single crystal at the time of reaction of the group II element and the group VI element, the impurities are liable to enter the stable sites. The higher activation rate is, therefore, obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a II-VI group compound semiconductor single crystal by cooling a melt to produce a single crystal.

[0002]

2. Description of the Related Art Among zinc-containing chalcogenide semiconductors, which are compounds of zinc and chalcogen elements such as sulfur, selenium, and tellurium, zinc selenide (ZnSe) is regarded as a promising material for blue light-emitting devices and is put to practical use. Therefore, researches such as epitaxial growth have been actively conducted. These epitaxial growths are usually made of GaAs, which has a relatively close lattice constant.
A substrate is used. This is because a high-quality ZnSe substrate that can be used for epitaxial growth has not been obtained. Another reason is that the ZnSe substrate usually has a high resistance, and a conductive substrate required for a light emitting element cannot be easily obtained, which is a big problem. Next, FIG.
A conventional method for forming a ZnSe substrate crystal by the Bridgman method will be described.

A heat shield 82 is placed in a cylindrical high-pressure vessel 81 filled with an inert gas such as argon. In this heat shield 82, polycrystalline ZnSe 83 as a main material and Ga simple substance 84 as a doping material are used. A heat-resistant container 85 filled with is placed. 86 is a shaft for supporting the heat-resistant container 85, 8
A heater 7 heats the heat-resistant container 85. First, the heat-resistant container 85 is heated by the heater 87 to dissolve the raw materials filled therein. Next, by lowering the shaft 86 supporting the heat-resistant container 85, a thermal gradient is given in the direction of cooling the raw material to make it into a single crystal, and a single crystal is obtained.

Most commonly, graphite is used as the material for the heat-resistant container. However, depending on the single crystal material, a reaction may occur at the contact surface between the melt and the inner wall of the heat-resistant container, or impurities such as carbon may be generated. Ceramic materials such as boron nitride (BN) and pBN are also used because they are mixed in a large amount in the crystal body.

However, the ZnSe single crystal obtained by such a conventional crystal growth method has a high resistance (10 ¹² Ωcm ^-1 or more), and even if a low resistance is achieved by heat treatment commonly called Zn treatment, a low carrier is obtained. Concentration (10 ^16-17 Only about cm ^-3 ) could be achieved.

[0006]

As described above, the conventional crystal growth method can provide only the II-VI group compound semiconductor crystal having high resistance and low carrier concentration, and the blue LE
There is a problem that it is not possible to provide a substrate having high conductivity as expected for D. Therefore, it is an object of the present invention to solve the above problems and provide a method for producing a II-VI group compound semiconductor single crystal exhibiting good conductivity with low resistance and high carrier concentration.

[0007]

In order to achieve the above object, the first invention is to provide a polycrystalline II-VI group compound semiconductor as a main material and a conductivity type of the II-VI group compound semiconductor as an auxiliary material. A step of accommodating impurities and a group II element to be determined in a crucible, a step of converting the main raw material and the auxiliary raw material into a melt in the crucible, and a II-VI group compound having a conductivity type by recrystallizing the melt. A method for producing a II-VI group compound semiconductor single crystal, comprising the step of forming a semiconductor single crystal.

The second invention is a polycrystalline material as a main raw material.
II-VI compound semiconductor, and impurities for determining the conductivity type of the II-VI compound semiconductor as a secondary material, a step of accommodating a II element, and a VI element in a crucible, the main material and the auxiliary material A method for producing a group II compound semiconductor single crystal, comprising: a step of forming a melt in a crucible; and a step of recrystallizing the melt to form a group II compound semiconductor single crystal exhibiting a conductivity type. Is provided.

[0009]

[Function] A polycrystalline II-VI group compound semiconductor as a main material,
As a starting material, a group II element, a group VI element, and a carrier impurity element are used as starting materials.
The group element and the group VI element react with each other at a temperature below the melting point of the compound, and the carrier impurity element is simultaneously taken in at this time.
Next, when the II-VI group compound polycrystal, which is the main raw material, is melted at a temperature equal to or higher than the melting point, the secondary raw material after the reaction is also melted at the same time, and in this process, the carrier impurities are uniformly incorporated at a high concentration.

Since carrier impurities are taken in during the reaction between the group II element and the group VI element, they easily enter stable sites as impurities. Therefore, a high activation rate can be obtained.

When only the group II element and the carrier impurities are used as the auxiliary materials, the group VI element is evaporated from the main raw material below the melting point of the polycrystalline II-VI group compound as the main raw material. The group II element and the group II element, which is an auxiliary material, react with each other and at the same time, carrier impurities are taken in.

[0012]

Embodiments of the present invention will now be described with reference to the drawings.
The details will be described. In the examples, the apparatus shown in FIG. 8 was used.

First, a first embodiment of the present invention will be described.
In this example, ZnSe was prepared as a II-VI group compound semiconductor single crystal exhibiting n-type conductivity. Among the auxiliary materials, Ga, which is a group III element, was used as an impurity that determines the conductivity type, and Ga metal was used as a starting material. FIG. 1 is FIG.
It is an enlarged view of the heat-resistant container 85 of the apparatus shown in FIG.

First, III was used as an auxiliary material in the heat-resistant container 5.
Ga metal 11 (0.2 g) which is a group simple substance, Zn metal 12 (1 g) which is a group II simple substance, Se simple substance 13 which is a group VI simple substance
(1g), Z which is a II-VI group compound semiconductor as a main raw material
nSe polycrystal 14 (120 g) is sintered boron nitride (B
The crucible manufactured by N) was sealed in a nitrogen-substituted glove box.

Next, the inside of the heating furnace of the vertical Bridgman method used for single crystallization is pressurized with nitrogen to 90 atm as an example of the pressurized range of 10 to 350 atm, and then heated to melt the raw material. Then, the inside of the heat-resistant container 85 was kept at 1550 ° C. for 1 hour, and then gradually cooled at 10 ° C./hour to solidify. In this step, the amount of the single crystal obtained was 121 g with respect to the amount of the semiconductor raw material charged of 122.2 g.

The thus-prepared ZnSe single crystal changed its appearance color to a reddish one as compared with the additive-free one, and was prepared by the conventional method in which Zn metal and Se alone were not charged as auxiliary materials. Metal-like precipitates as found in the prepared single crystal were not found on the surface or inside of the crystal.

FIG. 2 is a graph showing the results of analysis of the Ga concentration distribution in the ZnSe crystal prepared in this example.
The horizontal axis represents the length of the obtained crystal soul as a ratio, and the head portion of the obtained crystal soul is 0 and the tail portion is 1 (the same applies hereinafter). The vertical axis represents Ga concentration.

In this way, the straight body of the crystal is 10 ^18-20 cm ^-3 G
It was a concentration of a and it was observed that the particles were uniformly dispersed. For comparison, in the ZnSe crystal in which only Ga was added, precipitation of a metal substance containing a high concentration of Ga was observed at the bottom of the crystal and it was not sufficiently activated.

Next, the ZnSe crystal according to the present embodiment is melted Z
Heat treatment was performed at 700 ° C. in N. The heat treatment time, which conventionally required several tens of hours, was already 1 hour, and the n-type conductivity was already exhibited. As a result of the experiment, good characteristics were shown at about 700 ° C to 1200 ° C, but particularly high activation rate was shown in the range of 800 ° C to 900 ° C.

Next, after heat treatment was carried out at 850 ° C. for 16 hours, hole measurement was performed on the ZnSe crystal according to this example in which the crystal surface was mirror-polished. FIG. 3 is a graph showing the carrier concentration of this ZnSe crystal. The horizontal axis is the length of the crystal soul, which is expressed as a ratio. The vertical axis represents the carrier concentration.

Thus, the carrier concentration in the entire crystal is 10
^18-20 cm ^-3 or more, and the activation rate was 50% or more. For comparison, in the ZnSe crystal added with only Ga, the carrier concentration is 10 ¹⁸ cm even if the same heat treatment is performed.
^-3 or less, activation rate is up to 10%, most are 1%
It was below.

From the above results, it is clear that Ga is added with high efficiency in the method of manufacturing a ZnSe compound semiconductor according to this embodiment. In the case of adding Ga alone, unreacted and precipitated high concentration Ga compound inside and on the surface of the crystal is not included in the auxiliary raw materials, Zn metal and Se.
When the simple substance was bonded during the temperature rising process, Ga was effectively taken into the crystal, a high concentration addition of Ga and a high activation rate could be achieved, and a ZnSe compound semiconductor crystal with a high carrier concentration could be realized.

In this embodiment, Ga alone and Z are used as auxiliary materials.
n simple substance and Se simple substance were used.
Group III of Ga-Zn alloy is an alloy, similar effects with Ga ₃ Se ₂ compound semiconductors III-VI Group compound was obtained. Further, although it is difficult to handle, the same effect was observed when Ga, Zn, and Se were reacted in advance and added during crystal growth.

Further, in the present embodiment, Ga simple substance, Zn simple substance and Se simple substance were used at the same time as the auxiliary raw materials. However, similar effects were observed even when only Ga simple substance and Zn simple substance or Ga simple substance and Se simple substance were used as auxiliary raw materials.

In the present embodiment, ZnSe has been described as an example of the II-VI group compound semiconductor as the main raw material.
Similar effects were observed with nS, ZnS _x Se _1-x , and Zn _y Cd _1-y Se. Further, in this embodiment, Ga is used as the group III element which is the element that determines the conductivity type.
Similar effects were observed with Al and In which are group III elements.

Next, a second embodiment of the present invention will be described.
In this example, ZnSe was prepared as a II-VI group compound semiconductor single crystal exhibiting p-type conductivity. Li was used as a Group I element as an impurity that determines the conductivity type, and Li ₂ Se containing a Group VI element, Zn metal, and Se alone were used as starting materials. Since the present embodiment has substantially the same crystal growth apparatus and method as the first embodiment, description will be made with reference to FIG.

First, as raw materials, Li ₂ Se 11 (0.2 g) which is a group I-VI compound semiconductor as a subsidiary material, Zn metal 12 (1 g) which is a group II simple substance, and Se simple substance 13 which is a group VI simple substance.
(1 g), II-VI group compound semiconductor ZnSe as the main raw material
Polycrystal 14 (120 g) was sealed in a heat-resistant container 5 made of sintered boron nitride (BN) in a nitrogen-substituted glove box.

Next, the inside of the vertical Bridgman heating furnace used for single crystallization was pressurized to 90 atm with nitrogen and then heated to confirm the melting of the raw materials, and the heat-resistant container 5 described in FIG. Was maintained at 1550 ° C. for 1 hour, and then gradually cooled at 10 ° C./hour to solidify. In this step, the amount of the semiconductor raw material as an example was 122.2 g, and the amount of the single crystal obtained from them was 121.2 g.

The ZnSe single crystal prepared in this manner changed its appearance color to a reddish color as compared with the conventional non-added one, so that it was confirmed that it was effectively added to the crystal. Was also clear. Although the appearance color of the crystals changed, the transparency was not impaired, and metallic precipitates were not seen on the surface or inside of the crystals. FIG. 4 is a graph showing the Li concentration distribution in the ZnSe crystal prepared in this example. The horizontal axis represents the length of the crystal soul as a ratio, and the vertical axis represents the concentration of Li. In this way, the straight body part of the crystal is 10 ^18-19 The Li concentration was cm ⁻³ , and it was seen that Li atoms were uniformly diffused.

Next, the ZnSe crystal according to this example was heat-treated at 700 ° C. in Se vapor. The heat treatment time, which conventionally required several tens of hours, was already 1 hour, and the p-type conductivity was already exhibited. As a result of the experiment, good characteristics were shown at about 700 ° C to 1200 ° C, but particularly high activation rate was shown in the range of 800 ° C to 900 ° C.

Next, after heat treatment was performed at 850 ° C. for 16 hours, hole measurement was performed on the ZnSe crystal according to the present example in which the crystal surface was mirror-polished. FIG. 5 is a graph showing the carrier concentration of this ZnSe crystal. The horizontal axis represents the length of the crystal soul as a ratio, and the vertical axis represents the carrier concentration.

Thus, the carrier concentration in the entire crystal is 10 ¹⁷ cm
^-3 or more, and the activation rate was 50% or more.
For comparison, ZnS added with only Li alone as an auxiliary material
In the case of e crystal, the carrier concentration is 10 even if the same heat treatment is applied.
^{It was 17} cm ^-3 or less, the activation rate was 10% at the maximum, and most of it was 1% or less.

From the above results, it is apparent that Li is added with high efficiency in the ZnSe crystal prepared in this example. This is because when only Li alone is added as an auxiliary material, the vapor pressure of metallic Li is high, so that polycrystalline ZnSe
It is thought that this was because it was evaporated before it melted and was not effectively added to the prepared crystals. As described above, according to the present embodiment, the relatively high vapor pressure metal can be easily added. This is because the simple substance Zn and the simple substance Se, which are the auxiliary materials, effectively incorporate Li into the crystal during the binding in the temperature rising process, and can achieve a high Li concentration and a high activation rate. It is considered that the type ZnSe compound semiconductor crystal can be obtained.

In the examples, Li ₂ Se and Zn were used as auxiliary materials.
Although a simple substance, a simple substance of Se, and ZnSe polycrystal as the main raw material were used, the same effect can be obtained by using a Li—Zn alloy containing metal Li and a group II element as an element that determines the conductivity type instead of Li ₂ Se as the auxiliary raw material. The effect was obtained. Moreover, although it is difficult to handle, the same effect was observed when Li, Zn, and Se were reacted in advance and added during crystal growth.

As a raw material, Li alone, Zn alone,
And Se alone are not used at the same time, and Li alone and Z are used as auxiliary materials.
Similar effects were observed with only n, or only Li and Se.

In this embodiment, ZnSe was taken as an example of the II-VI group compound semiconductor, but ZnS, Z
Similar effects were observed with nS _x Se _1-x and Zn _y Cd _1-y Se.

Further, although Li is used as the group I element which is an element that determines the conductivity type in the present embodiment, the same effect can be obtained even with an alkali metal element containing the same group I element such as NaK and Cs having a high vapor pressure. It was seen.

Next, a third embodiment of the present invention will be described.
In this example, ZnSe was prepared as a II-VI group compound semiconductor single crystal exhibiting p-type conductivity. This was performed using N, which is a group V element, as an impurity that determines the conductivity type, and ZnN, which is a compound of N, as a starting material. Since the present embodiment has substantially the same crystal growth apparatus and method as the first embodiment, description will be made with reference to FIG.

First, Zn which is a II-V group compound is used as an auxiliary material.
N11 (0.2 g), Zn metal 12 (1 as a group II simple substance)
g), Se simple substance 13 (1 g) which is a VI group simple substance, ZnSe polycrystal 14 which is a II-VI group compound semiconductor as a main raw material
Heat-resistant container 5 made of sintered boron nitride (BN) (120 g)
It was enclosed in a glove box whose atmosphere was replaced with nitrogen.

Next, the interior of the vertical Bridgman heating furnace used for single crystallization was pressurized with nitrogen to 90 atm, and then heated to confirm the melting of the raw materials. It was kept for 1 hour, and then gradually cooled at 10 ° C./hour to be solidified. An example of the amount of semiconductor raw material charged in this step is 12
121.2 g of single crystal obtained from these at 2.2 g
Met.

The ZnSe single crystal prepared in this manner changed its appearance color to a reddish color as compared with the conventional additive-free one, so that it can be effectively added to the crystal from the appearance. Was also clear. Although the appearance color of the crystals changed, the transparency was not impaired. FIG. 6 is a graph showing the concentration distribution of N in the ZnSe crystal prepared in this example. The horizontal axis represents the length of the crystal soul as a ratio, and the vertical axis represents the N concentration. In this way, the straight body of the crystal is 10 ^17-18 The N concentration was cm ⁻³ , and it was seen that N atoms were uniformly diffused.

Next, the ZnSe crystal according to the present embodiment was melted Z
Heat treatment was performed at 700 ° C. in N. The heat treatment time, which conventionally required several tens of hours, was already 1 hour, and the p-type conductivity was already exhibited. As a result of the experiment, good characteristics were shown at about 700 ° C to 1200 ° C, but particularly high activation rate was shown in the range of 800 ° C to 900 ° C.

Next, after the surface of the ZnSe crystal according to this example, which had been heat-treated at 850 ° C. for 16 hours, was mirror-polished, hole measurement was performed. FIG. 7 is a graph showing the carrier concentration of this ZnSe crystal. The horizontal axis represents the length of the crystal soul as a ratio, and the vertical axis represents the carrier concentration.

Thus, the carrier concentration in the entire crystal is 10
^17-18 cm ^-3 or more, and the activation rate was 50% or more. For comparison, in a ZnSe crystal in which ZnN was not added as an auxiliary material even under a nitrogen pressure of 90 atm, the N concentration was 2 ppm or less, which was the measurement limit, and the carrier concentration could not be measured at all.

From the above results, the Zn prepared in this example was
It is clear that Se crystals are doped with N at high efficiency. Conventionally, when N alone is added in the atmosphere, Zn
Since it did not react with the Se melt at all, it was not incorporated into the crystal at all. Therefore, it was not effectively added to the prepared crystal, but according to the present example, addition of N, which is a gas element, could be easily performed. This is an auxiliary material Z
When n and Se alone combine during the temperature rising process, N is effectively taken into the crystal, a high concentration of Ga and a high activation rate can be achieved, and a ZnSe compound semiconductor crystal with a high carrier concentration can be realized. It is due to the fact.

In the examples, ZnN, Zn simple substance, Se simple substance and ZnSe polycrystal as the main raw material were used as the sub raw materials, but the same is used instead of N which is the group V element for determining the conductivity type.
Similar effects were observed with As and P which are V elements.

In this embodiment, ZnSe was taken as an example of the II-VI group compound semiconductor, but ZnS, Z
Similar effects were observed with nS _x Se _1-x and Zn _y Cd _1-y Se.

Further, when the auxiliary raw material is charged, it is desirable that the carrier impurities, the group II element, and the group VI element are arranged adjacent to each other. This is because these auxiliary raw materials react with each other below the melting point of the polycrystalline II-VI group compound which is the main raw material, so that the adjoining ones can effectively promote the progress of the reaction. It is preferable that the auxiliary raw material is arranged at the bottom of the crucible and the main raw material is filled on the auxiliary raw material. This is because the polycrystalline II-VI group compound is melted in the upper layer portion where the temperature is high, and the II-group element and the VI-group element as the auxiliary raw materials are prevented from evaporating. Further, when the carrier impurity is 1, the group II element and the group VI element of the auxiliary raw material are 10 or more, and when the total of the auxiliary raw material is 1, the main raw material is preferably 100 or more. Although the Bridgman method is used in each of the embodiments of the present invention, other synthetic methods such as the Czochralski method and the liquid sealing pulling method may be used.

[0049]

As described above, according to the present invention, a II-VI group compound semiconductor single crystal exhibiting a low resistance and a high carrier concentration and good conductivity can be prepared. It is possible to provide a substrate exhibiting good conductivity as expected for a blue LED using.

[Brief description of drawings]

FIG. 1 is a sectional view of a heat-resistant container used in the first, second, and third embodiments of the present invention.

FIG. 2 is a diagram showing a Ga concentration distribution of a ZnSe crystal prepared in Example 1 of the present invention.

FIG. 3 is a diagram showing a carrier concentration distribution of a ZnSe crystal prepared in the first example of the present invention.

FIG. 4 is a diagram showing a Li concentration distribution of a ZnSe crystal prepared in a second example of the present invention.

FIG. 5 is a diagram showing a carrier concentration distribution of a ZnSe crystal prepared in the second embodiment of the present invention.

FIG. 6 is a diagram showing an N concentration distribution of a ZnSe crystal prepared in a third example of the present invention.

FIG. 7 is a diagram showing a carrier concentration distribution of a ZnSe crystal prepared in the third embodiment of the present invention.

FIG. 8 shows an apparatus for producing a single crystal by the vertical Bridgman method.

[Explanation of symbols]

 11 An auxiliary material containing an element that determines the conductivity type. 12 Group II element as an auxiliary material 13 Group VI element as an auxiliary material 14 Main material

Claims (2)

[Claims] 1. A step of accommodating a polycrystalline II-VI group compound semiconductor as a main raw material, and an impurity and a group II element that determine a conductivity type of the II-VI group compound semiconductor as a sub-raw material in a crucible, the main raw material And a step of forming an auxiliary material into a melt in the crucible, and a step of recrystallizing the melt to form a II-VI group compound semiconductor single crystal exhibiting a conductivity type, II -Method for producing Group VI compound semiconductor single crystal. 2. A step of accommodating, in a crucible, a polycrystalline II-VI group compound semiconductor as a main raw material, and impurities, a II group element, and a VI group element that determine the conductivity type of the II-VI group compound semiconductor as an auxiliary raw material. And a step of forming a melt of the main raw material and the auxiliary raw material in the crucible, and a step of recrystallizing the melt to form a II-VI group compound semiconductor single crystal exhibiting a conductivity type. A method for producing a II-VI group compound semiconductor single crystal, which is characterized.