Anomalous temperature dependence of fundamental gap of AgGaS 2 and AgGaSe 2 chalcopyrite compounds

Abstract

We have studied the temperature variation of the fundamental gap energy of the chalcopyrite-like ternary semiconductors AgGaS 2 and AgGaSe 2 from reflectivity measurements performed between 5 K and room temperature. The temperature evolution of the gap energy is found to be clearly different from that observed for the II-VI and III-V zincblende-like binary semiconductors. The temperature coeffecients are positive under 80 K and negative above 100 K with values clearly smaller than those encountered for the II-VI and III-V binaries. Results are discussed taking into account the hybridization between the d orbitals of Ag and the p orbitals of anion (S or Se).