SYNTHESIS OF CHALCOPYRITE SEMICONDUCTORS AND THEIR SOLID-SOLUTIONS BY MICROWAVE IRRADIATION

Chalcopyrite semiconductor compounds, M(I)M(III)E(2) (M(I) = CU, Ag; M(III) = Al, Ga, In; E = S, Se, Te), have been prepared by microwave irradiation of appropriate mixtures of the pure elements in a domestic microwave oven and characterized by X-ray diffraction (XRD) and energy-dispersive X-ray (EDX) analysis. Alloys of the type CuInSxSe2-x and CuInSexTe2-x (0 < x < 2) analyzed by XRD show that solid solutions are formed and there is no site preference for one chalcogenide over another. The crystallographic lattice parameters a and c were found to increase linearly rather than parabolically with increasing amounts of selenium. The exact atomic ratios of each element, as determined by EDX techniques, indicate that in all reactions the products are indium-rich p-type semiconductors. Attempts to prepare alloys of the type CuInSxTe2-x (0 < x < 2) resulted in a mixture of CuInS2, CuInTe2, and CuInS0.3Te1.7. The formation of CuInS0.3Te1.7 appeared to be independent of the S:Te reagent ratio and possibly represents a limit of the sulfur solubility in CuInTe2. It does demonstrate that metastable phases usually precluded by traditional syntheses can be prepared by microwave irradiation. The formation of continuous sulfide-selenide and selenide-telluride solid solutions but not sulfide-telluride alloys is discussed with respect to the relative ionic radii of the chalcogenides and the 2-c/a (Delta) values. While AgInSe2 forms only the tetragonal chalcopyrite phase, AgInS2 and AgInTe2 formed additional orthorhombic and cubic phases, respectively. No evidence for the formation of AgAlE(2) could be obtained although CuAlE(2) (E = S, Se) were formed, albeit as poorly crystalline samples.