Transmission Electron Microscopy of II-VI/III-V Semiconductor Heteroepitaxial Interfaces
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TRANSMISSION ELECTRON MICROSCOPY OF II-VI/III-V SEMICONDUCTOR HETEROEPITAXIAL INTERFACES D. LI, AND N. OTSUKA School of Materials Engineering, Purdue University, West Lafayette, IN 47907 J. QIU, J. GLENN Jr., M. KOBAYASHI, AND R. L. GUNSHOR School of Electical Engineering, Purdue University, West Lafayette, IN 47907
ABSTRACT Interfaces of pseudomorphic (100)ZnSe/GaAs and (100)CdTe/InSb heterostructures grown by molecular beam epitaxy have been studied by transmission electron microscopy. High resolution electron microscope images show dark bands with thicknesses of one or two monolayers at the interfaces. The interfaces appear as bright lines in dark field images of the 200 type reflections, while they become dark lines in dark field images of the 400 type reflections. These observations are explained by assuming the existence of interfaces layers of II12VI 3 compounds which have structural vacancies in the sublattices of the group III atoms.
1. INTRODUCTION In recent years, a significant progress has been made in the growth of II-VI/III-V semiconductor heterostructures by molecular beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD). Heterostructures having high structural qualities are grown by utilizing closely lattice matched systems such as ZnSe/GaAs, CdTe/InSb, and ZnTe/GaSb. The growth of these heterostructures has raised a possibility of the development of new novel electronic devices. In addition, the possibility of the development of light emitting devices of wide-gap II-VI semiconductors are presently being explored by utilizing these heterostructures.
The realization of II-VI/III-V semiconductor heterojunction devices, however, requires the preparation of heteroepitaxial interfaces having extremely good electronic properties. For achieving this goal, important results have been obtained in a recent study by Qian, et al. [1]. This study has demonstrated the feasibility of the preparation of ZnSe/GaAs heterojunctions whose interface state densities are comparable to those of GaAs/(Al, Ga)As heterojunctions. For the preparation of these heterojunctions, the growth of pseudomorphic ZnSe epilayers on GaAs epilayers and post-growth annealing were employed. In a more recent development, as-grown heterostructures having interfaces with the similar quality have been obtained by growing ZnSe on As-deficient GaAs surfaces without the need for the post-growth annealing [2]. These results, which have shown the change of the interface electronic properties by the post-growth annealing or by the change of the surface stoichiometry of GaAs epilayers, suggest a certain form of modification of ZnSe/GaAs interface from the abrupt one. Earlier studies of ZnSe/GaAs [3,4 and CdTe/InSb [5] heterostructures have suggested the formation of stable II12VI 3 compounds such as Ga 2Se3 and In 2Te 3 at these interfaces. These studies have utilized spectroscopic techniques for the analysis of the interfaces; to date, no structural study of these heteroepitaxial interfaces has been reported. In this paper, we prese
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