Study of the electronic structure of model (110) surfaces and interfaces of semi-infinite III-V compound semiconductors: The GaSb-InAs system

Abstract

This paper presents the results of a study of the electronic structure of model (110) surfaces and interfaces of semi-infinite III-V compound semiconductors, with specific application to the GaSb-InAs system. The description of the individual solids is sought within the empirical tight-binding method and combined with the Green's-function technique to account for their semi-infinite nature. Surface states are found to exist for ideal (110) surfaces, consistent with previous results obtained via the use of the finite-slab method. Results presented for the interface between two semi-infinite III-V semiconductors are the first to be reported and indicate the possible importance of the nature of the band-edge discontinuity of the heterojunction. It is shown that the expected unusual band lineup of the GaSb-InAs system gives rise to a finite density of states at the interfacial atomic planes, throughout the region of the bulk fundamental band gaps. Consequently, no interfacial barrier exists in this heterojunction. It is noted that this behavior of the GaSb-InAs heterojunction occurs in a regime of thickness of the individual materials which, in practice, is not accessible via the usual finite-slab method. Results of the influence of the interface geometry on the interface electronic structure are reported. For the interface characterized by interfacial chemical bonds of bulk bond strengths, we find no interface states in the fundamental-band-gap regions. This is found to be the case for both usual and unusual band lineup. Variations in the interface bond strengths, simulating the influence of the interface geometry, show that interface states first appear for unusually large departures from bulk bond strengths. It is thus suggested that interface states in lattice-matched III-V semiconductor heterojunctions are unlikely to arise solely due to variations in intrinsic chemical bonding effects. Results for interface states associated with dangling-bond are presented. It is found that the energy position of such states is relatively insensitive to those changes in surrounding geometry which do not appreciably alter the surface bond strengths of the host materials. These results suggest that the most likely origin of interface states for the class of systems investigated here is the presence of defects involving relaxation of the surrounding interfacial atoms.