Electrical Properties of (CaSr)F2/GaAs(111)B Interfaces Grown by Molecular Beam Epitaxy: Realization of Unpinning

Abstract

Electrical properties of lattice-matched (CaSr)F₂/GaAs(111)B interfaces grown by molecular beam epitaxy (MBE) are investigated. C-V and ICTS results are presented that clearly indicate for the first time that the GaAs surface level is unpinned in metal/fluoride/GaAs (MIS) structures. The surface potential can be moved toward the conduction band edge up to E _c-0.1 eV. The minimum interface state density is estimated to be around 1×10¹¹ eV^-1 cm^-2. In contrast, strong pinning is observed for MIS diodes using (100)-oriented substrates or lattice-mismatched fluorides. The realization of unpinning and accumulation is attributed to interface coherence and dangling bond termination. The present analysis demonstrates that pinning-free GaAs MIS structures can be successfully achieved if the interface is prepared properly.