The method of obtaining optical materials of the compounds of zinc and cadmium

 

(57) Abstract:

The invention relates to a technology for obtaining compounds of zinc and cadmium, suitable for the manufacture of optical components, transparent in a wide spectral range. The inventive method consists in the manufacture of samples from the melt recrystallization pressing powders or vapor deposition and subsequent thermal processing in the melt tin. And before you pre-heat treatment, the surface of each sample is covered with a layer of viscous suspensions having adhesive property with respect to the processed material and consisting at its core of inert substances, with the inclusion of particles of material of the main component of the processed chalcogenide zinc or cadmium. Deposited on the surface of the sample, the suspension is dried prior to immersion in the tin. Suitable as the inert mass of a viscous suspension to use clay-like substance, for example kaolin. The technical result consists in the improvement of the optical characteristics of workpieces from compounds of zinc and cadmium, is solved by creating the optimal technological conditions of heat treatment, including the reduction of losses, the Mat is of a. 7 C.p. f-crystals, 2 PL.

The invention relates to a technology for obtaining compounds of zinc and cadmium, in particular zinc selenide, La Sylphide zinc or cadmium telluride, suitable for the manufacture of optical components, transparent in a wide spectral range.

Billet optical material obtained from the melt recrystallization by hot pressing of powders or by vapor deposition on a heated substrate.

For the manufacture of optical components requires a material with high performance for chemical purity, optical homogeneity and transparency, which is achieved as various improvements of technological processes, and additional subsequent heat treatment of the material obtained.

Samples of zinc selenide and zinc sulfide, obtained, for example, by hot pressing or grown from the vapor phase, show that, despite careful selection of process conditions, materials have significant shortcomings. These include uneven coloring preparations according to the area, the presence of inclusions in the form of opaque or diffusing defects, low transmittance in the visible region of the spectrum, porosity.

In French patent /1/ describes the method of processing optical elements made of zinc sulfide and zinc selenide, which is based on hot isostatic pressing (CIP) of the samples, which leads to the improvement of their optical characteristics. The patent States that the ISU processing reduces scattering and absorption in the material. When this occurs, the establishment of a chemical composition that is closer to stoichiometric.

In this way also serves to isolate the workpiece by wrapping it in a sheet made of an inert substance that helps regulate vapor exchange between the product and the inert gas. As inert materials proposed graphite, tantalum sheet, copper and platinum. The application of the latter gives the best result.

High temperature at the ISU processing creates the conditions for diffusion of impurities from the volume to the sample surface, and the pressure helps to reduce porosity. The ISU processing concrete samples zinc selenide and zinc sulfide has led to significant improvements in their optical characteristics. In relation to the selenide zinc temperature initial sample was yellow and cloudy. After treatment, hot isostatic pressing, he became the green-yellow and transparent. The transmittance of the sample at =0.5 µm changed from 5% to handle up to 50% after treatment (sample thickness is not specified). The above-described method of the ISU processing requires expensive processing equipment.

The /2/ marked effect of reducing the absorption of zinc selenide under isothermal annealing in pairs selenium, and selenium melt. The greatest result is achieved by annealing in the melt selenium, it was found that the concentration of pores, impurities, and excess own components has not changed, however, significantly decreased the content of carbon, polluting the crystal growing process. Modes annealing source is not specified.

Article /3/ the influence of the initial composition of defects in undoped zinc selenide on its electrical properties during processing in the melt selenium. We used the crystals grown from the gas phase and with different resistivity (~0.1 to 10 Ohm·cm) after annealing in the melt selenium for 80 hours at 900 and 100°C. With increasing annealing temperature the influence of the initial content of anionic vacancies on the conc is s zinc selenide, grown from the melt and subsequent annealing in a liquid zinc and zinc vapor. Annealing was carried out in a sealed quartz ampoule at TOTG=980°C for several hours. After this liquid zinc was poured into the other end of the ampoule and the cooling of the crystals was carried out with the furnace at a rate of ~1501 deg/hour. The results of the processing of the crystals showed the diffusion of impurities from the bulk of the crystal in the liquid zinc and zinc from the liquid phase in the crystal. The same results were achieved in the processing in zinc vapor. Annealing in zinc vapor was carried out at TOTG=1000°C and RZn=1 ATM, and pairs of selenium at TOTG=900°C and pSe=1 ATM. After annealing in zinc vapor was observed qualitatively the same changes of properties of zinc selenide crystals, as and when annealing in liquid zinc.

The above processing methods of zinc selenide crystals to improve electrical and optical characteristics of the material require proper technological regimes, including those associated with high temperature during the discharge of molten zinc or selenium, present in the process gas atmosphere, for example selenium with known harmful effects on human health.

When processing of the crystals in liquid lead with the addition of zinc is the healing of zinc vacancies in the crystal due to diffusion of atoms of zinc from solution in the crystal, which reduces the concentration of acceptors, compensating shallow donor impurity.

In this way the heat treatment of the crystals was carried out in a pre-evacuated to 10-4mm RT.art., and then sealed quartz ampoules. Annealing in liquid lead and lead with the addition of zinc was carried out for 72 hours at a temperature of 900°C. the Crystals after heat treatment had a significantly lower mobility of charge carriers.

In the prototype, as in the previous counterparts, are complex procedures associated with the sink melts at high temperatures; the processing vapor components, NAIA same sealed quartz ampoules limits the size of the workpieces processed materials. In addition, processing of materials at high temperatures leads to their dissolution in molten metals or pairs of components that leads to a strong degradation of the surface of the processed material or unmanaged etching in the form of holes or through holes in the thickness of the material /6/. The last case is when the etching thickness of the material through is absolutely unacceptable in the manufacture of optical components.

The task of the invention is to improve optical characteristics of samples chalcogenides of zinc and cadmium by creating optimal technological conditions of heat treatment and, as a consequence, the reduction of material losses associated with the degradation of surface or etching thickness of the workpieces chalcogenides, ensuring the maximum possible harmless conditions, simplification of the process.

The task is solved by the method of producing optical materials of the compounds of zinc and cadmium, which consists in the manufacture of samples from the melt recrystallization pressing powders or vapor deposition and subsequent heat treatment to melt the fusible metal is tin, and pre-poverkhnostyami material and consisting at its core of inert substances, with the inclusion of particles of material of the main component of the processed chalcogenide zinc or cadmium, and dried prior to immersion in the melt.

The main inert mass of a viscous suspension, it is advisable to produce a clay-like substance. This substance may be kaolin.

Heat treatment zinc selenide is carried out in the molten tin at a temperature of 900-1000°C for 30-45 hours.

Heat treatment of zinc sulfide is carried out in the molten tin at a temperature of 850-950°C for 20-45 hours.

Heat treatment of cadmium telluride is carried out in the molten tin at a temperature of 700-950°C for 40-70 hours.

Viscous suspension comprises particles of the main component of the processed material in the form of dispersed powder of the corresponding chalcogenide zinc or cadmium with particle sizes of 0.1-5 microns.

Viscous suspension, made of kaolin, typically includes fine particles of the corresponding chalcogenide zinc or cadmium in the ratio of 1:1 by weight of the kaolin.

The proposed method allows you to create more sophisticated handling of materials, since tin has a lower temperature odinakovoi melt temperature, for example 900°C, the tin has a significantly lower vapor pressure over the melt - 10-9mm RT.art., compared to lead - 10-2or zinc (>10+1) mm RT.article The vapor pressure determines the volatility of the melt, which is deposited on the cold parts of the vacuum unit.

Temperature: 900-1000°C for zinc selenide, 850-950°C for zinc sulfide and 700-950°C for cadmium telluride are sufficient for the extraction of most of the impurities from the material, and the degree of extraction is determined by the time of heat treatment, which is 30-45, 20-45 and 40-70 hours - depending on the type of processed material (ZnSe, ZnS or CdTe).

To prevent undesirable interaction of the processed material with the melt (dissolution) is a temporary isolation using a viscous suspension which is prepared on the basis of claylike substance, for example, kaolin and fine powder of the corresponding chalcogenide zinc or cadmium. Clay-base suspension provides sufficient adhesion (adhesion) with the surface of the workpiece, creating a temporary tightness at the heat treatment in reply chalcogenide zinc or cadmium, dissolving in the tin until it is saturated, reduces the dissolution of the processed material on virtually no.

A specific example of implementation of the method

For the preparation of protective suspension is mixed sample of kaolin with water until a homogeneous viscous mass, then add equal weight kaolin fraction of fine powder of zinc selenide and mix thoroughly. The suspension is applied to the sample by a continuous layer, for example, a brush with subsequent drying at room temperature. In case of gaps in the coating operation may be repeated. Then the samples are heated in air up to 200 to 250°C, placed in a crucible with a pre-rastavlennymi tin (melt temperature from 300 to 350°C), covered with a graphite lid and press down the load, for example, of molybdenum or tungsten to the total immersion of the samples in the tin. The crucible is set in a vacuum oven.

After evacuation to a residual pressure of 5·10-2mm RT.article furnace with crucible heated to 400°C, and then putting argon to a pressure of 0.5 ATM and raise the oven temperature (melt) to 920°C, When the temperature argon pressure above the melt is increased and its release is live and open. Tin drained and samples inertial cool down to room temperature. Next, the samples undergo mechanical processing (grinding, polishing), spectrophotometric and visual inspection.

The application of the method contains no great difficulties, because the use readily available materials and tools. The process of heat treatment is not associated with the high temperatures of the discharge of the melt, minimized evaporation of the melt and dissolution of the processed material. The remains of the protective coating can be easily removed flat scraper.

Processing in the molten tin is subjected samples with pronounced spotting, i.e., different in color coloration or color heterogeneity in the visible region of the spectrum, and low transmittance in the wavelength range of 3-14 μm or visible region of the spectrum.

The results of the particular implementation of the heat treatment of ZnSe in the melt tin as described above:

Example 1. Samples of polycrystalline ZnSe obtained vapor deposition, had visual defects, unevenness in color and tone enable. Simultaneous processing in the molten tin was subjected to two series - coated proposed suspension and without covered. Obrazca samples to a depth of 5 mm All samples acquired uniform, monochromatic yellow-green color, mottling and tone disappeared, increased transmittance.

Example 2. Samples of polycrystalline ZnSe (#1 and # 2) had a low transmittance in the wavelength range =3-14 μm. After heat treatment, the transmittance increased significantly. The transmittance (in %) before and after heat treatment in the bark of tin are presented in table 1.

Example 3. Sample polikristallicheskogo ZnSe No. 3 had prior to the heat treatment of low transmission in the visible and near infrared region (0.5 to 1.2 μm) and a reddish tint. The ratio of the transmittance 1/2for biscotasi lengths will (1=0.5 µm and 2=0.55 m) characterizing the color of the sample amounted to 0.72. After heat treatment, the transmittance is increased, the sample acquired a yellow-green color, value 1/2decreased. Quantitative results are presented in table 2.

Sources

1. Patent 2497361 (France). Blanks of polycrystalline zinc sulfide and zinc selenide with improved optical properties and how they are processed to improve their optical characteristics. C. B. Willingham, J. Pappis. Publ. 28.12.1981.abstracts of the VII all-Union meeting “Crystalline optical materials”. L., 1989, S. 57.

3. Krasnov A. N. etc. the Influence of the initial composition on the concentration of holes at annealing selenide zinc in the molten selenium // technical physics Letters, 1993, T. 19, vol.1, S. 89-91.

4. Akimova I. Century. etc. Influence the stoichiometry of the single-crystal compounds AND11INV1the characteristics of a semiconductor laser pumped by an electron beam - proceedings of the Lebedev physical Institute, 1987, I. 177, S. 142-171.

5. Ivanov, and others Photoluminescence of annealed crystals of zinc selenide // Journal of applied spectroscopy, 1979, I. XXX, vol.3, S. 459-463.

6. Hall R. solubility of semiconductor compounds AND111Bvin melts of group III elements In kN.: Technology semiconductor compounds. M, Metallurgy, 1967.

1. The method of obtaining optical materials of the compounds of zinc and cadmium, which consists in the manufacture of samples from the melt recrystallization pressing powders or vapor deposition and subsequent heat treatment to melt the fusible metal is tin, and preliminary surface of each sample is covered with a layer of viscous suspensions having adhesive property with respect to the processed material and consisting at its core of inert is whether cadmium, and dried before immersion in the molten tin.

2. The method according to p. 1, characterized in that the main inert mass of a viscous suspension consists of a clay-like substance.

3. The method according to p. 2, characterized in that the main inert mass of a viscous suspension is made of kaolin.

4. The method according to p. 1, characterized in that the heat treatment zinc selenide is carried out in the molten tin at a temperature of 900-1000°C for 30-45 hours

5. The method according to p. 1, characterized in that the heat treatment of zinc sulfide is carried out in the molten tin at a temperature of 850-950°C for 20-45 hours

6. The method according to p. 1, characterized in that the heat treatment of the cadmium telluride is carried out in the molten tin at a temperature of 700-950°C for 40-70 hours

7. The method according to p. 3, characterized in that the viscous suspension includes fine particles of the corresponding chalcogenide zinc or cadmium in the ratio of 1:1 by weight of the kaolin.

8. The method according to p. 1, characterized in that the viscous suspension includes corresponding chalcogenide zinc or cadmium in the form of dispersed powder with particle sizes of 0.1-5 microns.



 

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