Annealing Effects on Impurity Band Conduction of ZnSnAs2 Epitaxial Films

Abstract

Un-doped II-IV-V2 ZnSnAs2 thin films have been grown epitaxially on semi-insulating InP(001) substrates by molecular beam epitaxy using a substrate temperature of Ts=300°C. In-situ reflection high-energy electron diffraction observations during the growth revealed streaky patterns indicating an atomically flat surface. After verification of the resulting stoichiometry by electron probe microanalysis and the crystalline structure by high-resolution X-ray diffraction studies, three samples were cleaved from the as-grown sample and subsequently annealed at temperatures of 300, 320, and 340°C for two hours with face-to-face proximity capping by GaAs wafers to simulate an arsenic atmosphere. The temperature dependence of the Hall coefficient of the as-grown sample and the samples annealed at 300 and 320°C showed equal carrier concentration at the exhaustion and freeze-out ranges, suggesting the validity of the impurity band model for these samples. The measured temperature dependence of the Hall coefficient and resistivity, analyzed within the framework of the impurity band model proposed by Isomura, revealed decreasing total carrier concentration p and impurity band carrier mobility μa, increasing acceptor activation energy Ea and maximum valence band mobility μv with increasing annealing temperature.