JPS61183106A - Process and device for synthesizing cadmium compound - Google Patents

Abstract

PURPOSE:To synthesize a Cd compd. contg. no impurity with high yield by adding Cd portionwise in a small amt. in the form of liquid drop to a melted group VI element in the stage of synthesizing a compd. of Cd with a group VI element. CONSTITUTION:A crucible 1 is placed in a vessel 5, and a molten body 2 of a group VI element such as Te, Se, S, etc., is formed by heating with a main heater 4, and the surface of the melt is covered with molten B2O3. Solid Cd 12 is fed to an ampule 7 at the top of the vessel and heated with a subheater 8 to melt Cd having low melting point, and the vapor of Cd is introduced into a refluxing device 9 at the top of the vessel. The Cd vapor rises upward through a first zone 15 of the refluxing device, enters a second zone 16 through a perforated hole 18, raised upward, further, through the third zone 17, where it is transformed to liquid by cooling, but a part is vaporized again by being heated by the vapor of Cd from the ampule 7 and raised to the top 10 of the device. The vapor enters a communicating pipe 11 at the side part, and enters a liquid phase 2 of Te, etc., in the form of liquid drops, etc., by being liquefied and rises through the liquid Te 2 in the form of fine foams. During this stage, the vapor forms a CdTe compd. in high yield.

Description

Detailed Description of the Invention (7) Technical Field The present invention relates to a method and apparatus for synthesizing cadmium compounds such as CdTe, CdSe, and CdS.

(a) Prior art and its problems In order to make a single crystal of It-Vl group semiconductor,
It is necessary to synthesize polycrystals from simple elements of group elements.

(2) Polycrystalline synthesis of group V compounds includes the boat method and the crucible method.

Synthesis of GaAs polycrystal using a crucible will be explained. FIG. 2 is a schematic cross-sectional view of a GaAs polycrystal synthesis apparatus.

A crucible 21 is provided in a pressure-resistant container 20, and a heater 22 is installed around it. Inside the crucible 21 is a Ga melt 24.
Contains. It is heated by the heater 22 and becomes liquid.

Above the crucible 21, there is an As container 26.
contains solid As27. There is a sub-heater 25 around it. The communication pipe 2 is directed downward from the As container 26.
8 extends and is inserted into the crucible 21.

The Ga melt 24 is covered with B2O3, which is a liquid capsule. This is to prevent As from escaping. The container 20 is filled with N2 gas and high pressure is applied.

The As 27 is heated by the sub-heater 25.

As becomes a gas, descends through the communication pipe, and enters the Ga melt. In this, GaAs is synthesized.

The Ga melt is heated to about 1240°C.

The As vapor rises in the melt 24 from the lower end of the communicating tube, and reacts with Ga on the way.

The above device is for GaAs. A similar method can be used for the synthesis of InP.

It appears that the apparatus shown in Figure 2 can be used to synthesize CdTe. Pour the Te melt into the crucible and transfer it to container 26 (made of quartz).
A similar synthesis may be possible if Cd is added to . C
d melts, becomes a melt, descends through the communication tube 28, enters the Te melt, and synthesizes CdTe.

However, when synthesizing Cd compounds such as CdTe, A
The melting point of Cd, which corresponds to s, is as low as 320°C. Moreover, the vapor pressure of Cd at this temperature is low. Therefore, Cd enters the Te melt in a liquid state. This is different from the case where As enters the Ga melt as a gas.

If it is a gas, the amount added per hour is small and the probability of reaction is high.

However, if an apparatus such as the one shown in FIG. 2 is used, the CD becomes a liquid and is poured into the Te melt in large quantities.

Since the Te melt is at a high temperature, Cd is rapidly heated and vaporized. It vaporizes and becomes large bubbles, which instantly rise in the melt and are released. Even if it is held down by B2O3,
It passes through this easily and escapes out of the crucible.

In this case, Cd is wasted and the synthesis yield becomes extremely low.

These drawbacks are due to the low melting point and low vapor pressure of Cd. It is necessary to form fine bubbles in the melt to increase the reaction time and reaction area.

Furthermore, if it falls into the melt as liquid Cd,
The impurities contained in Cd will be mixed into the Te melt as is. It is necessary to refine Cd.

In the end, in order to synthesize CdTe, GaAs, InAs
.

Synthesizers such as InP cannot be used as is.

(1) Purpose: To provide a method for synthesizing a Cd compound with a high synthesis yield in which a large amount of Cd does not enter the melt as a liquid at once and impurities are not mixed. purpose.

2) Structure and function The Cd compound synthesis method of the present invention directly converts Cd melt into Te.
Rather than pouring it into the melt, Cd is vaporized and guided to a reflux device, and while repeating the vaporization and liquefaction process, it gradually enters the melt as a liquid, allowing it to react slowly with the melt. .

FIG. 1 is a sectional view of the synthesis apparatus of the present invention.

A crucible 1 is supported within the container 5 by a lower shaft 6. A main heater 4 is provided around the crucible 1. The crucible 1 contains a melt of a group III element, which is covered with a liquid capsule 3. The liquid capsule 3 is, for example, B2O3. The raw material melt 2 contains Te, Se,
S, etc., but will be described below as a Te melt.

An ampoule 7 containing solid Cd is provided diagonally above the crucible 1. A sub-heater 8 is provided on the side of the ampoule 7 in order to heat the Cd12.

Rather than immediately lowering the communicating tube downward from ampoule 7,
A reflux device 9 is provided above the ampoule 7.

The reflux device 9 consists of a triple cylinder, and three solid spaces are provided inside.

At the outermost side, a first zone 15 occurs. The Cd vapor rising from the ampoule 7 rises here.

A second zone 16 occurs in the middle. The first zone 15 and the second zone 160 communicate with each other through an upper narrow through hole 18. The Cd vapor enters the second zone 16 through the through hole 18 .

A third zone 17 occurs at the innermost depth. It communicates with the second zone 16 at its lower end. The cadmium vapor descends through the second zone 16 and ascends through the third zone, but is cooled along the way. As it is cooled, most of it returns to liquid form. A portion of the liquid is transferred to the second zone 16.
It accumulates at the bottom of the.

The remainder is returned to ampoule 7.

What accumulates at the bottom of the second zone 16 is the reed pull 7.
It is vaporized again by the heat of the Cd vapor rising from the
Ascent through the third zone 17. and the upper part of the reflux zone 10
leading to.

The Cd liquid returned to the ampoule 7 is heated again and returned to the reflux device 9. Some of this is cooled again and liquefied in the first zone 15, but some of it proceeds to the second zone 16 and third zone 17.

- Now, the Cd vapor that has reached the upper part 10 of the reflux zone is cooled and liquefied here. Most of the liquid falls directly below the bottom of the second zone and accumulates there.

However, some steam also enters the communication pipe 11 extending laterally from the upper part 10 of the reflux zone. This steam is transferred to the communication pipe 1
It is cooled and liquefied in 1.

Although only a small amount of liquid is liquefied in the communication pipe 11, it becomes small droplets and falls down the communication pipe 11, but it becomes a thin stream and flows down the communication pipe 11.

In any case, the Cd liquid is introduced into the Te melt 2 little by little.

Cd droplets enter the melt 2 little by little.

The temperature of the Te melt in the crucible is about 1100°C.

The temperature of Cd 12 in the ampoule is approximately 330°C.

The temperature of the Te melt must be higher than the melting point of CdTe, resulting in a high temperature.

However, the temperature of Cd droplets is naturally lower than the boiling point (765°C). If this happens, it will suddenly fall into the melt, which has a temperature difference of about 335°C or more.

Since the droplets are small, they tend to form fine bubbles when heated rapidly. This is because heating occurs rapidly and the entire liquid instantly reaches a high temperature.

The fact that it becomes fine bubbles means that CdTe
It is convenient for the synthesis of

One is that the diameter of the Cd% bubble is small and the total surface area is relatively large, and the contact area that participates in the reaction becomes large.

Another reason is that because the bubbles are small, the ratio of buoyancy to viscous resistance is small, and the bubbles do not easily float up in the melt. Since it stays in the melt for a long time, the reaction time becomes longer and the probability of forming CdTe increases.

A high pressure of several tens of atm of nitrogen gas is applied to the liquid capsule 3. Since the liquid capsule 3 presses the Te melt under such high pressure, the buoyancy of the bubbles becomes even smaller by /J'1.
The upward movement becomes weaker.

The nitrogen gas pressure is, for example, about 50 atm.

Thus, the amount of Cd implanted is extremely small.

In the reflux device 9, Cd repeats evaporation and liquefaction, and only a portion of the Cd enters the Te melt, becomes microbubbles, reacts with Te, and becomes CdTe.

(4) Effects (1) The amount of Cd injected into the melt per unit can be reduced.

In the case shown in FIG. 2, all of the liquefied Cd enters the melt and a large amount is injected.

In the present invention, a reflux device is provided above the Cd ampoule, where the Cd is repeatedly evaporated and liquefied, and only a portion of the Cd enters the melt through the communication tube.

Since the injection amount is small, there are fewer bubbles in the melt.

If the bubbles are small, the ratio of surface area to mass becomes large, and the contact area becomes large, so the probability of reaction with the melt increases spatially.

When the diameter of a bubble is D, the weight of Cd contained therein is proportional to the cube of D, and the surface area is proportional to the square of D. The contact area per unit weight is proportional to 1/D. Therefore, it is important that D is small.

Furthermore, if the bubbles are minute, viscous resistance (proportional to the first power of D) becomes dominant over buoyancy (proportional to the third power of D).

Therefore, the bubbles have almost no buoyancy and remain in the melt for a long time.

Therefore, the probability that Cd reacts with the melt increases over time.

In this way, the probability that Cd will chemically react increases spatially and temporally.

Explain why small bubbles result when the injection amount is small.

Suppose that a bubble with a diameter exists in the melt.

Let the surface tension coefficient be σ. The bubble pressure Pi is the melt pressure P. bigger. Since the pressure difference ΔP (=Pi-P0) is consistent with the surface tension, cds =
ΔP dV (1). SSv is the surface area and volume of the bubble.

From (1), we get σ. Melt pressure P. is approximately equal to the pressure applied by inert gas (N2 gas) and is constant. However, the pressure Pi inside the bubble depends on the temperature of the Cd bubble. This temperature Ti is 320°C or more and 1100°C or less.

When a large amount of Cd is injected, the Ti content is low because the Cd becomes bubbles before it is sufficiently heated. If it is injected little by little, T1 will be high because it will be heated excessively.

Pt = ρRTi (3). ρ is the number of moles of gas per unit volume. The higher the temperature, the greater the bubble pressure Ps.

Then, it can be seen from equation (2) that the diameter of the bubble becomes smaller.

(2) By adjusting the power of the sub-heater,
The amount of Cd implanted can be controlled arbitrarily.

(B) Cd is purified. Impurities do not enter the melt. Evaporation and liquefaction are repeated in the reflux device, and once the evaporated material is liquefied, it enters the communication pipe. Therefore, there is no contamination of impurities. This is because the reflux device has a distillation purification function.

(Power) Applications Can be used to synthesize polycrystals of CdTe, CdSe, and CdS.

(To) Example Put 500 g of To and 3240 g of B2O into a crucible.

CdTe is synthesized using an ampoule containing 580 g of Cd with a reflux device attached above.

These raw materials, an ampoule, and a reflux device are set in a pressure-resistant container.

Vacuum is applied to approximately 2 x 10 Torr. Increase the temperature of the crucible to 200°C.

Thereafter, nitrogen gas is introduced into the container and the pressure is increased to 5Q atm. Increase the crucible temperature to 500°C. At this time, Te and B2O3 in the crucible are in a molten state.

Next, the ampoule 7 and the reflux device 9 are lowered as a whole until the tip of the communication tube 11 of the reflux device 9 comes into contact with the Te melt 2 in the crucible 1.

The temperature of the crucible is further increased to 1100°C.

The temperature inside the ampoule 7 is set to 330°C by the sub-heater 8.
Heat until. Distillation of Cd begins. Cd becomes a melt.

The CD vapor evaporated from the Cd melt in the ampoule 7 repeats evaporation and liquefaction in the reflux device 9. Most of it was refluxed into the ampoule, and a part of it passed through the reflux device, turned into Cd droplets, and fell into the Te melt, starting a reaction.

The Cd injection was completed in about 2 hours.

Thereafter, the crucible temperature was maintained at 1100° C. for 3 hours.

After this, it was cooled. A CdTe crystal was obtained. The yield of CdTe crystals was 95%. This CdTe polycrystal is pty
pe, and the specific resistance was 10 Ωcm.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of a cadmium compound synthesis apparatus according to an embodiment of the present invention. FIG. 2 is a longitudinal cross-sectional view of a GaAs synthesis apparatus. 1 ・・・・・・・・・ Crucible 2 ・・・
...... Te melt 3 ...... Liquid capsule 4 ...
・・・・・・ Main heater 5 ・・・・・・・
・・・ Pressure-resistant container 6 ・・・・・・・・・
・Lower shaft 7 ・・・・・・・・・ Ampoule 8 ・・・・・・・・・ Sub heater 9 ・・・・・・・・・ Reflux device 1
0 ...... Upper reflux zone 11 ...
...... Communication pipe 12 ......
...... Cd 15...... First zone 16... Second zone 17... Third zone 18... ...Through hole invention
Patent applicant Toshihiro Kotani Patent applicant Sumitomo Electric Industries Co., Ltd. Application “1” Valve 1
・Pi ζpa.

Claims (2)

[Claims] (1) Put Te, Se, or S Group VI elements and liquid capsules in a crucible 1, heat them with the main heater 4, and
A group I element melt 2 and a liquid capsule 3 covering it, and Cd 12 placed in an ampoule 7 are heated by a sub-heater 8 to form a Cd melt and Cd vapor, and the Cd vapor is refluxed by a reflux device 9.
The evaporation and liquefaction are repeated through the reflux device 9, and a portion of the Cd vapor is introduced into the group VI element melt 2 as droplets from the reflux device 9 through the communication pipe 11. While applying high pressure to the liquid capsule with an inert gas, the melt is A method for synthesizing a cadmium compound, characterized by synthesizing a cadmium compound in a liquid 2. (2) A crucible 1 containing a Group VI element melt 2 and a liquid capsule 3, a main heater 4 provided around the crucible 1, and a C
Ampoule 7 containing d12 and Cd in ampoule 7
12; a reflux device 9 provided above the ampoule 7 to evaporate and liquefy the Cd vapor and reflux it; A cadmium compound synthesis apparatus characterized by comprising a communication pipe 11 leading into a cadmium compound and a pressure-resistant container 5 surrounding the communication pipe 11.