JPS6283396A - Method for growing compound semiconductor crystal - Google Patents

Abstract

PURPOSE:To make the compsn. of a fused raw material uniform and to grow the crystal film of a compd. semiconductor which is free from uneven thicknesses and uneven compsn. by applying ultrasonic oscillation to the material for the compd. semiconductor and a device contg. said material. CONSTITUTION:A base 4 contg. a substrate 5 for growth in a recess 8 and a carbon boat 3 contg. the material 5 for the compd. semiconductor in a barrel 6 are disposed in a quartz tube 2 on which a heater 1 is wound. Electric power is then thrown to the heater 1 to fuse the material of a low m.p. in the material 5; at the same time, an ultrasonic generator 11 is operated to apply the oscillation in an arrow direction to the carbon boat 3 via a fixing bar 10 to diffuse the melt having the unfused component existing between the material beginning to fuse and the unfused material at a high concentration into the fused material and to quickly fuse the material 5. The compd. semiconductor is thereafter epitaxially grown.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for growing crystals of compound semiconductors of the ■-■ group or II-VI group by the LPE (liquid phase epitaxy) method.

[Prior art and its problems]

When growing compound semiconductors by the LPE method, materials are rarely used in the form of alloys that have been melted in advance with a predetermined composition; instead, several elements that make up the compound semiconductor are grown separately in predetermined amounts. Either weigh each time, or make a compound of at most two elements, and then add another element to the compound of two elements in other combinations to form a predetermined composition. It is common to weigh. This is due to the following reasons.

Unlike other growth methods, such as the pulling method or Bridgman method, in which an alloy crystal with the same composition is directly grown from a material with a stoichiometric composition, when growing with the LPE method, the constituent elements are By containing a large amount of the material with the lowest vapor pressure and using it as a so-called solvent to lower the melting point of the entire material, this suppresses the vapor pressure of other materials with high vapor pressure, thereby suppressing compositional fluctuations due to their evaporation. This is the case when trying to obtain a thin film crystal having a predetermined composition on top. In this method, since a large amount of one element is contained, the composition naturally deviates significantly from the stoichiometric ratio. Therefore, if a large amount of the material is synthesized in advance in a large container, the large amount of these elements will be liberated and precipitated, and will not be uniformly distributed in the 11 alloy but will be localized. Therefore, if a part of the required amount is cut off, the material will have a composition different from the predetermined composition.

Therefore, in the LPE method, it is necessary to weigh the material each time a crystal is grown.

Next, as an example of a compound semiconductor, Hg I-, lCd )l Te which is a mixed crystal of HgTe and CdTe, x=0.2
I will point out the problem by giving a case. As mentioned earlier, thin film crystals with the compositions Hgo, eCdo, and 2Te are
For growth on a CdTe substrate using the PE method, the material composition in terms of atomic ratio is Hg:0.200. CD: 0.00
9°Te: 0.791. Incidentally, the composition ratio when grown by the Bridgman method is Hg:0.4, Cd
:0.1.

Te: 0.5. Comparing the two, it can be seen that in the material composition for LPE, the amount of Te is quite large, and the amount of Hg and Cd is quite small.

Hg is used as a method for preparing the material composition for LPE.

A method of weighing a predetermined amount of each of Cd and Te as single element metals, and a method of weighing a predetermined amount of each of Cd and Te as single element metals, and a method of weighing a predetermined amount of each of Cd and Te as single element metals, and a method of weighing a predetermined amount of each of Cd and Te as a single element metal, and a method of weighing a predetermined amount of each of Cd and Te as a single element metal, and a method of weighing a predetermined amount of each of Cd and Te as a single element metal, and a method of weighing a predetermined amount of each of Cd and Te as a single element metal.
CdTe, which is a compound of
There is a method of weighing a predetermined amount of e. In the former case, Hg with a high vapor pressure is added alone, so the Hg gradually evaporates until the temperature reaches approximately 500°C, where the entire liquid becomes a melt.
This causes a non-negligible change in composition. On the other hand, since the latter has the HgTe0 form as a compound, evaporation of Hg is considerably small. However, the melting point of CdTe is about 1090℃
Therefore, it takes some time for the solvent Te, which has a melting point of 450° C., to melt CdTe.

On the other hand, since HgTe has a melting point of 670°C, it melts into Te before CdTe. Therefore, while the CdTe is melting, Hg begins to evaporate, so if the whole is melted over a long period of time, composition deviations due to a lack of Hg cannot be avoided. Since the LPE method is usually carried out in a one-atmosphere hydrogen stream, which is called the open tube method, this Hg evaporation is unavoidable.
In addition, all constituent elements must be uniformly mixed. However, current LPE apparatuses do not have methods for this purpose, and there is a problem that the uniformity of the composition is insufficient.

Listing the specific drawbacks of conventional crystal growth using a material composition of HgTe, cdTe, and Te as a solvent, it takes about 2 g to melt the entire 2 g of material.
It took time, and the material composition changed due to the evaporation of Hg during this time, and the X value of the grown crystal thin film was about 0.3. Furthermore, the thickness of the grown film on the 1×1 cffl substrate varied depending on the location, which is thought to be due to the non-uniformity of the melt composition. When the melting time was set to 1 hour to reduce the amount of Hg evaporation, cross-sectional observation of the melt after solidification revealed that some CdTe and HgTe remained unmelted. Incidentally, unlike the LPE method, in the Bridgman method, materials are vacuum-sealed in a quartz ampoule or the like, and the electric furnace is repeatedly turned upside down while being melted in the electric furnace, so the materials are forcibly mixed and melted. A melt with a uniform composition can be obtained in a short time.

[Purpose of the invention]

The purpose of the present invention is to provide LPE equipment, which has not conventionally had active means for promoting melting and mixing of raw materials, to suppress the evaporation of Hg and improve the uniformity of the composition of the molten raw materials. Another object of the present invention is to provide a method for growing a compound semiconductor crystal film with less unevenness in thickness and composition.

[Structure of the invention]

The method for growing a compound semiconductor crystal of the present invention is characterized by applying ultrasonic vibration to the material and the device containing the same in the step of melting the material in order to grow the compound semiconductor crystal by the LPE method.

[Function/principle of the invention]

FIG. 1 schematically depicts an apparatus for carrying out the growth method of the present invention in order to explain the operation and principle of the present invention. An LPE growth device is housed in a quartz tube 2 around which a heater 1 is wound, and this growth device mainly consists of a carbon boat 3 and a stand 4. A recess 8 for accommodating a growth substrate 7 is provided on the stand. Further, fixing rods 9 and 10 for fixing the growth device at the correct position in the quartz tube 2 are fixed via O rings, and an ultrasonic oscillator is attached to one end of the fixing rod 10 for transmitting ultrasonic vibrations to this. 1
1 is connected. Power is applied to the heater 1, and at the same time as some of the low melting point materials of the material 5 begin to melt, the ultrasonic generator 11 is operated, and ultrasonic waves are applied to the carbon boat 3 via the fixed rod 10 in the direction shown by the arrow. Gives vibration. Then, the melt with a high concentration of unmelted components existing between the material that has begun to melt and the unmelted material quickly diffuses into the melted material, and the concentration of the melt surrounding the unmelted material decreases, resulting in Melting of unmelted material is accelerated and accelerated.

Furthermore, mixing is promoted by vibration.

〔Example〕

Next, the present invention will be explained in detail by way of examples.

Hg:C as the growth material 5 in the barrel 6 of FIG.
d: Te ratio is 0.200:0.009:
The compound HgTe, Cd so that it becomes 0.791
A total of 2g of Te was accommodated. The reason why this compound form was adopted is because, as already explained, when Hg is used as a single element, evaporation starts already at the initial stage of heating, causing a change in the material composition. CdTe as the substrate 7
After the substrate is placed in the recess 8 and hydrogen is introduced into the quartz tube 2, the heater 1 is energized to start raising the temperature, and the temperature of the carbon boat 3 reaches the melting point of Te, which is the lowest among HgTe, CdTe, and Te. When reaching the ultrasonic generator 11 (3MHz)
was operated to apply ultrasonic vibration to carbon boat 3.

After the melting point of growth material 5 reached 490° C., the vibration was continued for another hour at this temperature. After completing the normal growth process, we observed the cross section of the remaining growth material and found that there was no remaining HgTe or CdTe, and the CaO value of the grown crystal thin film (about 10 μm thick) was 0.21. Despite the short melting time, better results were obtained than in the case of 2-hour melting without ultrasonic vibration.

〔Effect of the invention〕

As detailed above, according to the present invention, it is possible to completely melt the growth material in a short time, and it is possible to prevent elements with high vapor pressure from evaporating, so that the composition is quite close to the predetermined composition. A crystalline thin film of a compound semiconductor having the same composition can be obtained.

[Brief explanation of drawings]

FIG. 1 is a diagram f9 schematically showing an apparatus for carrying out the method of the present invention. 1 ...... Heater 2 ...... Quartz tube 3 ...... Carbon boat 5 ...
...... Growth material 6 ...... Barrel 7 ...... Substrate 9.10 ... Fixing rod

Claims (1)

[Claims] (1) A method for growing a compound semiconductor crystal, which comprises applying ultrasonic vibration to the material and a device containing the same in the step of melting the material in order to grow the compound semiconductor crystal by liquid phase epitaxy.