HETEROLAYERS OF NON-TYPICAL HEXAGONAL CdTe MODIFICATION AS THE MAIN COMPONENT OF FUNCTIONAL DEVICES
[3. Technical sciences]
Author: Mazur Tetiana, PhD, Associate Professor, Ivano-Frankivsk National Technical University of Oil and Gas, Ivano-Frankivsk, Ukraine; Mateik Galina, PhD, Associate Professor, Ivano-Frankivsk National Technical University of Oil and Gas, Ivano-Frankivsk, Ukraine
One of the basic materials for devices of modern functional electronics is cadmium telluride . Based on it, a number of different types of devices have been obtained, the properties and characteristics of which are determined precisely by the physical and technical parameters of the material used. The direct band structure of cadmium telluride in combination with a sufficiently large band gap (Eg=1.50 eV) is an important condition for obtaining a material with high radiation efficiency in the near infrared region. In addition, highly efficient solar-to-electrical energy converters have been obtained on its basis, and such detectors are widely used in various optoelectronic systems .
Hetereshars (HL) were obtained by isothermal annealing in pairs of isovalent elements. Under certain conditions, the corresponding atoms of the base substance were replaced, which led to the name of the isovalent substitution method. Preliminarily, the base substrates of crystals of II-VI compounds underwent known processes of chemical-mechanical treatment, were loaded into quartz ampoules and sealed off. In them, the substrate of the base material and the canopy of the corresponding diffuser were located on opposite edges. Isothermal annealing was carried out with a suitable location of the ampoule in the furnace, Fig. 1.
Isothermal annealing of the base crystals α-CdSe was carried out at Та= 8000С in a saturated vapor of an isovalent (up to Se) element Te. Equilibrium conditions were obtained, according to which the diffusion of the isovalent impurity (IVІ) occurs and the atoms of the base substance of the same valency are replaced. A new chemical compound α-CdTe is formed on the surface of α-CdSe according to the reaction
where the indices "Ts" and "G" correspond to the solid and gaseous states of the reagents.
Fig. 1. Temperature distribution and position of ampoules during the production of diffusion layers. 1 - substrates of the initial material, 2 - sample.
In the case of the α-CdSe base compound, a α-CdTe/α-CdSe heterostructure with time-stable properties is formed. Annealing of hexagonal α-CdS substrates in a pair of isovalent element Te was also carried out to obtain an α-CdTe/α-CdS HS by the reaction
The characteristic light yellow color of the base substance made it possible to detect the boundary between it and the resulting dark HL of cadmium telluride by observing the end face of the structure under a microscope. Based on its position, it is possible to estimate the thickness of the HL, which is d = 75 μm upon annealing ta = 1.5 h and temperature T = 820°C. The optimality of certain regimes of the annealing process is confirmed by the results of the preparation of β-CdTe heterolayers of a typical cubic modification. They were obtained by the above technology under certain conditions according to the reaction
Obtaining heterostructures with layers of typical cubic β-CdTe and atypical hexagonal α-CdTe crystal lattices is confirmed by the results of studies of their band structure.
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