Intrinsic defects and the influences on electrical transport properties in quaternary diamond-like compounds: Cd2Cu3In3Te8 as an example

Over the years, the fact that the quaternary diamond-like thermoelectric materials show much lower carrier mobilities than ternary compounds remains mysterious. In this work, by adopting first-principles defect chemistry and electrical transport calculations, the fundamental origin of the difference on carrier mobility between quaternary and ternary diamond-like compounds is addressed, exemplified by Cd2Cu3In3Te8. The results of defect chemistry show that the main intrinsic defects in quaternary compound Cd2Cu3In3Te8 are substitutional defects, i.e., CdIn and CdCu, differing from the copper vacancy defect in ternary Cu-based compound such as CuInTe2. The low defect formation energies in Cd2Cu3In3Te8 result in high defect concentrations, which is caused by the similar atomic radii and electronegativities between CdIn and CdCu. Further calculations show that the low-energy defects are mainly located around the valence band maximum in Cd2Cu3In3Te8. The electrical transport calculations, considering both the acoustic phonon scattering and ionized impurity scattering, demonstrate that mainly due to the higher concentration of the ionized defects, the mobility of the quaternary Cd2Cu3In3Te8 is much lower than that of ternary CuInTe2. Our work sheds light on the intrinsic defects in quaternary diamond-like compounds and their influence on charge transport.