DIRECT OBSERVATION OF THE INITIAL NUCLEATION AND EPITAXIAL-GROWTH OF METASTABLE CUBIC GAN ON (001)GAAS

We report on the direct observation of the initial nucleation and the resulting microstructure of GaN deposited on GaAs(001) by plasma-assis ted molecular beam epitaxy. Using high-resolution transmission electro n microscopy, we demonstrate that, despite the extreme lattice mismatc h between these two materials, GaN nucleates in the metastable cubic p hase with a well-defined orientation relationship to the substrate and a sharp heteroboundary. The preference of the metastable phase in the initial stage of growth is discussed in connection with a coincidence lattice for the epitaxy-induced interface structure of the initial Ga N nuclei. (C) 1997 American Institute of Physics.