Effect of pulsed hydrogen and helium plasma irradiation on the formation of solid solutions in the thin-film CdTe/CdS heterosystem

Abstract

The interphase interaction of cadmium sulfide and cadmium telluride thin film layers under irradiation with pulses of hydrogen and helium plasma was investigated by the X-ray diffraction method. CdS/CdTe heterosystem samples were obtained by the hot wall method on glass substrates with a transparent FTO electrode. During deposition of CdS layers 0.3–0.32 µm thick, the temperature of the evaporator zone was 590 °C, and the substrate temperature was 395 °C. CdTe layers 3.8–4.0 µm thick were deposited at an evaporation zone temperature of 520 °C and a substrate temperature of 497 °C. After deposition, the “chloride” treatment of the heterosystem was carried out. The “chloride” treatment consisted in the deposition of a cadmium chloride film 0.7 μm thick on the surface of a CdTe by thermal vacuum evaporation without heating the substrate and by annealing the entire structure in air at a temperature of 410-415 °C for 20 min. The composition of the solid solutions was determined from the lattice period according to Vegard's rule. In the initial state, along with the cubic phase of cadmium telluride, the presence of CdTe1-xSx solid solutions with a sulfur concentration of 3 % and 8.2 % is observed. After irradiation of the CdS/CdTe heterosystems with hydrogen plasma pulses, the entire base layer turned into a solid solution with a sulfur concentration of 3 %. At the same time, two more phases of CdTe1-xSx solid solutions with sulfur concentrations of 6 % and 11.5 % were observed. The relative concentration of the cadmium telluride phase in the initial state was 84 %, after irradiation with hydrogen plasma pulses it was 82 %. In the initial state, the phases of solid solutions with sulfur content of 3 % and 8.2 % had relative concentrations of 7 % and 9 %, respectively; after irradiation, their relative concentrations became 15 % and 3 %, respectively. After irradiation of the CdS/CdTe heterosystem with helium plasma pulses, the entire base layer turned into a solid solution with a sulfur concentration of 1.5 %. In this case, two more phases with a sulfur concentration of 3.7 % and 7.9 % were observed. The relative concentration of cadmium phase telluride after irradiation with hydrogen plasma pulses decreases to 79 %. After irradiation, the relative concentration of the phase of solid solutions with sulfur contents of 3 % and 8.2 % increases to 17 % and 12 %, respectively. The experimentally observed difference in the evolution of the phase composition of the CdS/CdTe film heterosystem under irradiation with hydrogen and helium plasma pulses may be due to the fact that irradiation with more massive helium atoms leads to a greater thermal effect, which causes melting.