CHARACTERIZATION OF GAAS-LAYERS GROWN BY LOW-TEMPERATURE MOLECULAR-BEAM EPITAXY USING ION-BEAM TECHNIQUES

The stoichiometry, crystallinity, defect concentration, and the excess As lattice location in GaAs layers grown by molecular beam epitaxy at low growth temperatures (less-than-or-equal-to 300-degrees-C) were studied using ion beam techniques. The excess As concentration in the layers was measured by particle induced x-ray emission and was found to increase as the growth temperature was lowered. Excess As concentrations up to 1.5 at. % were measured in layers grown at 190-degrees-C. After annealing at temperatures higher than 400-degrees-C under As overpressure, the excess As atoms coalesce to form As precipitates as revealed by transmission electron microscopy. Ion channeling on the unannealed layers grown at 200-degrees-C revealed that they have good crystalline quality with a large fraction of the excess As atoms sitting at interstitial sites close to the normal As sites in the lattice. The rest of the excess As atoms are believed to be in an As(Ga) antisite position.