Heteroepitaxial deposition of Group IIa fluorides on gallium arsenide

The epitaxial deposition of fluoride films has been a subject of research interest because of their potential for integrated electronic and electro-optic device applications. We report here our recent results on the investigation of (100)BaF2-GaAs growth. Our approach differs from the conventional method by addressing the problem at the atomic layer level, especially at the interface between the deposited material and the substrate. These investigations have revealed that an interfacial chemical reaction is important in the heteroepitaxy process. As a result of this chemical reaction, an atomic Ba layer is formed on the GaAs surface. It is this Ba-template layer that enables two dimensional, molecular layer-by-layer growth of the BaF2 film. Films thus grown are of a high epitaxial quality which appears to be limited only by the quality of the GaAs surface. For BaF2 on GaAs, (100) growth is favored over (111) growth. This is contrary to earlier results by other investigators. It is concluded that the conventional approach to heteroepitaxial growth, relying on lattice match and surface energies is not applicable, at least for the fluoride films. This can be understood from the atomic and molecular structure of Ba and BaF2. Implications of these results to the understanding of the heteroepitaxial process, especially involving large lattice mismatches, and to the development of new materials and technologies will be discussed.