Electron diffraction studies of long-range order in AlxGa1-xAs

Abstract

We have recently found by electron diffraction that Ga and Al atoms can form an ordered sublattice during a continuous and uniform growth of AlxGa1-xAs thin crystals. Such long-range order has never before been observed in any III-V semiconductor alloys. Important questions are thus raised concerning the equilibrium phase of that system and the stability of certain types of artificially grown superlattice structures. The long-range order was found in thin layers of AlxGa1-xAs (with 0.15 ≤ x ≤ 0.80) grown epitaxially on GaAs substrates using metal-organic vapor-phase epitaxy (MOVPE) or molecular beam epitaxy (MBE) techniques under a range of growth temperatures and employing certain substrate orientations. The ordered state is reached during a continuous co-deposition of Al, Ga, and As at high temperatures without any artificial imposition of special growth sequences. It is thus likely that the ordered structure may represent an equilibrium and thermodynamically stable state.