STUDY OF PESO - PHOTORESISTIVE CHARACTERISTICS OF TlInSe2 SINGLE CRYSTALS

Objective. The aim of the study is to establish the patterns and mechanisms of the effect of various impurities on the tensoresistive characteristics of TlInSe2 single crystals, as well as in solid solutions based on it. When studying the piezophotoresistive characteristics of TlInSe2 single crystals, it will determine the nature of the effect of uniaxial elastic deformation on the electrical, photoelectric and tensoresistive properties of TlInSe2 crystals. Methods. Crystals synthesized by fusing the components in accordance with stoichiometry in evacuated (~ 10-4 mm Hg) and sealed quartz ampoules were used for the study. Highly pure elements thallium (Tl - 000), indium (In - 000) and selenium (Se - high purity grade - 17 - 4) were used as initial components for the synthesis. Single crystals were grown by the improved Bridgman method, the crystallization front velocity varied from 0.5 to 0.9 mm / h. The samples required for the study were prepared by cleaving the grown single crystals from an ingot by the simplest indentation with a sharp knife, the blade thickness of which is ≤ 0.01 mm, along two mutually perpendicular planes of natural cleavage. The samples were in the form of rectangular parallelepipeds with dimensions of 10x10x0.25 mm. Thus obtained needle crystals, without any additional processing were ready for welding contacts. Two methods were used to solder mechanically reliable ohmic contacts on these blanks: a) fusion of indium in a stream of inert gas, followed by brazing of copper (or nickel) wires (ø = 0.01 mm). b) direct spot welding of the corresponding wires with a capacitor discharge to the ends of the blanks heated in a flow of an inert gas. The second method turned out to be more efficient and reliable (especially for moderate temperatures). Plates of steel 45 with a thickness of 0.5 - 1.0 mm and a length of 20 - 80 mm served as calibration beams for the glued sensors. The surface of the substrate according to the processing class was at least 7. Findings. The nature of the influence of uniaxial elastic deformation on the electrical, photoelectric and tensoresistive properties of TlInSe2 crystals is studied. It has been established that in the case of uniaxial compression along the [001] direction, the dark and photoconductivity of the samples increase, and on the contrary, decrease in case of stretching. Moreover, the maxima of the spectral photosensitivity due to direct optical transitions at the point G at K = 0, do not change. The long-wavelength limit of intrinsic photoconductivity decreases with compression and increases with stretching which indicates the multi-valley nature of the band electronic spectrum of TlInSe2 crystals. Conclusions. Under uniaxial compression of TlInSe2 crystals in the [001] direction, their band gap increases. As a result, the Fermi level shifts and the concentration of electrons at r-centers increases, which leads to an expansion of the linear sections of the lux - ampere characteristic. It was found that the absolute value of the photocurrent in positively deformed samples increases, and in negatively deformed ones it decreases in comparison with the un deformed sample. In this case, the maximum of the photocurrent does not change, which indicates that the width of direct transitions in TlInSe2 crystals remains unchanged at different types of deformation