Germanium monocrystal growing method

FIELD: crystal growing.

SUBSTANCE: method comprises growing germanium monocrystals from melt onto seed followed by heat treatment, the latter being effected without removing monocrystals from growing apparatus at temperature within 1140 and 1200 K during 60-100 h, temperature field being radially directed with temperature gradient 3.0 to 12.0 K/cm. Once heat treatment comes to end, monocrystals are cooled to 730-750°C at a rate of at most 60-80 K/h. Monocrystals are characterized by emission scattering at wavelength 10.6 μm not larger than 2.0-3.0% and extinction not higher than 0.02-0.03 cm-1, which is appropriate for use of monocrystals in IR optics.

EFFECT: allowed growth of germanium monocrystals with high optical characteristics.

3 ex

 

The technical field

The invention relates to a method of growing from the melt of crystals Germany.

The level of technology

A method of obtaining semiconductors, including Germany (GB 755845 A (ASS ELECT IND), 29.08.1956), including the melting of the source material in the crucible and then crystallization of the melt on a rotating seed. The method is used to create p-n junctions by separation of the ingot from the same melt and subsequent placement in the melt of the other conductivity type. To eliminate defects in the crystal structure resulting from rapid cooling, the ingot is annealed for some time at a predetermined temperature, thereby reducing the concentration of defects. The method can not be directly used to obtain single crystals of germanium, which is used in infrared optics; stringent temperature conditions for the formation of the ingot significantly reduce the structural perfection of the crystal lattice and degrade electrical, optical and other properties.

The closest is essentially a method of growing single crystals of Germany from the melt by Czochralski method and the use of additional heat treatment of single crystal (G. Gafni, M. Azoulay, S. Shiloh et al. Large Diameter Germanium Single Crystals for Infrared Optics // Optical Engineering. 1989. V.28. No. 9. R-1007). The single crystals of Germany for optical applications (in ykrasna optics) diameter 159-200 mm were grown by the Czochralski method and then thermoablative. In single crystals Germany analyzed the heterogeneity of the refractive index and the value of the transfer function modulation. The goal of treatment was to increase the optical homogeneity of the material and the reducing optical loss. The goal was achieved by applying an optical annealing of the samples, which was conducted by heating to a temperature of 450°C, holding at this temperature for several days and further cooled to room temperature at a speed of 2°in a minute.

One of the important optical characteristics of the materials used in optics scattering of radiation by the authors has not been considered and analyzed. It is known that the dislocation structure of Germany (dislocations and dislocation defects such as small-angle boundaries, slip lines) can result in optical Germany to significant scattering of infrared radiation. High density of dislocations and especially the unevenness of their distribution do not provide acceptable optical parameters - high transmittance of radiation at a wavelength of 10.6 μm and sufficiently small scattering of radiation. In some cases these parameters, the single crystals of Germany are unsuitable for use in infrared optics. Authors use low-temperature (450° (C) annealing has no influence on the dislocation structure of the ur, this effect may be substantially only in the field of plasticity Germany (at temperatures above 600° (C), the maximum effect will be observed near the melting temperature (943°).

The invention

The basis of the invention was the task of reducing the scattering of radiation at the wavelength of 10.6 microns, while maintaining or even improving the level of optical transmittance. The task performed by annealing, which is part of the whole process of obtaining a single crystal from the melt loaded in the crucible to retrieve the crystal from the installation. At the final stage was carried out annealing grown from the melt of the crystal without its extraction from the plant growing. Annealing was carried out at a temperature close to the temperature of crystallization (1210)for 60-100 hours in the mandatory presence of a temperature gradient directed along the radius of the single crystal. Thus, the temperature of the Central part of the single crystal and its periphery were significantly different.

Short description

Technological cycle of growing single crystals of germanium with annealing consists in the following: in a graphite crucible installation pre-loaded chemically potraviny annoucement germanium. In structurally set the monocrystalline seed crystal, oriented in the desired Krista is iographica.com direction (usually < 111>). Installation cultivation is sealed. Turns on the cooling water supply, the installation creates the necessary vacuum. Turns on the heater resistance. Germanium is melted, then its temperature is reduced to create the required undercooling of the melt. The seed is lowered into the melt, followed by growing the single crystal. After growth of the single crystal, the average temperature of the single crystal is 1140-1200 K. the Average temperature is defined as the temperature difference at the periphery and in the center of the single crystal. Cooling installation, structurally and power of the heater is adjusted in such a way as to create and maintain the necessary temperature difference between the center of the single crystal and its periphery. The essence of this regulation is the creation of the desired temperature gradient within 3-12 To see the gradient Magnitude is selected depending on the diameter of the single crystal.

At this temperature the crystal is maintained at the installation for 60-100 hours (depending on diameter). In General, the mode of annealing the single crystal depends on its diameter. The increase of the diameter of the grown ingot leads to increasing the time of annealing, to reduce temperature gradients and reduce the average temperature. These gradients and prodoljitel the particular annealing established empirically on the basis of results of determination of the optical characteristics of single crystals, the main of which in this case was the scattering of radiation at the wavelength of 10.6 microns.

After exposure of the single crystal at the same temperature, the temperature is reduced, and the reduction of up To 730-750 occurs at a rate of not more than 60-80/hour.

After the cooling of the single crystal is extracted, processed and transmitted to determine the required specifications.

Examples of implementation of the method

Example 1

1.1. The single crystal without the use of the invention:

length - 160 mm; diameter - 60 mm;

scattering of 10.6 microns in the Central part of the single crystal is 8.5%;

absorption <0,02 cm-1.

1.2. The single crystal with the use of the invention (with annealing):

length - 150 mm; diameter - 58mm;

the annealing time of 60 hours;

the temperature gradient - 11/cm;

average temperature - 1165;

scattering of 10.6 microns in the Central part of the single crystal is 2.5%;

absorption <0,02 cm-1.

Example 2

2.1. The single crystal without the use of the invention:

length - 40 mm; diameter of 132 mm;

scattering of 10.6 microns in the Central part of the single crystal - 6,0±1,0%,

on the periphery of 10.0±2,0%;

absorption at 10.6 μm <0,02 cm-1.

2.2. The single crystal with the use of the invention (with annealing):

length 46 mm; diameter of 132 mm;

the annealing time is 72 hours;

the temperature gradient of 5 K/cm;

among the latter temperature - 1180;

scattering of 10.6 μm to 2.0±0,5%;

this rate is homogeneous;

absorption at 10.6 μm <0.015 g cm-1.

Example 3

3.1. The single crystal without the use of the invention:

length - 28 mm; diameter - 150 mm;

scattering of 10.6 microns in the Central part of the single crystal is 6.5±0,5%,

on the periphery of 10.0±1,0%;

absorption <0,025 cm-1.

3.2. The single crystal with the use of the invention (with annealing):

length - 29 mm; diameter - 150 mm;

the annealing time - 80 hours;

the temperature gradient of 4 K/cm;

average temperature - 1190;

scattering of 10.6 μm and 1.5±0,5%;

this rate is homogeneous;

absorption at 10.6 μm <0.015 g cm-1.

Industrial applicability

The application of the method has significantly improved optical properties of single crystals of germanium used in the IR devices. Essentially, this germanium was possible to use those devices, where poor data on scattering of radiation were not given the opportunity to create the devices.

The single crystals obtained by the proposed method is applied not only in new developments, but also in mass production in industry.

A method of growing single crystals of Germany from the melt on a seed crystal with a subsequent heat treatment of the single crystal, characterized the eat, the heat treatment is conducted without removing the crystal from the plant cultivation at a temperature of 1140-1200 To within 60-100 h in the presence of directed along the radius of the single crystal temperature gradient in the range of 3.0 to 12.0 K/cm, after which the single crystal is cooled to 730-750 To speeds of no more than 60-80 K/h



 

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