Phase behaviour and homogeneity ranges of chalcopyrite-type compound semiconductors

Differential thermal analysis (DTA) has been applied to study the homogeneneity regions of I-III-VI2 and II-IV-V-2 chalcopyrites such as CuInS2 (roquesite) and ZnGeP2. They sensitively changed their thermal behaviour adding small amounts of elemental or binary constituents to stoichiometric material. ZnGeP2 showed a congruent melting behaviour (m(p) = 1035(+/-3)degrees C) but did not exhibit solid-solid phase transitions as reported for other chalcopyrites. The homogeneity region was smaller than 0.25mole %. CuInS2 exhibited a nearly congruent melting point at 1093(+/-3)degrees C. The maximum of the liquidus at 1100(+/-3)degrees C of the join CuS-InS was shifted by 1-1.5 mole% to the CuS-side. DTA peak intensities related to latent heat of solid-solid phase transformations at 980(+/-3)degrees C and 1047(+/-3)degrees C were significantly attenuated by adding 2 mole% copper or indium sulfides to the ternary. At temperatures in the range from 500 to 680 degrees C missing transformation points of the binaries CuS and InS indicated the boundaries of the homogeneity region which can extend to both sides of roquesite up to 1.5 mole% InS. At room temperature the homogeneity of roquesite: ranges from less than or equal to 0.25mole% InS to 1.5mole% CuS.