Recent work, on As rich GaAs buffer layers grown at low temperatures by molecular beam epitaxy (MBE), shows that this material has electronic and materials properties that differ from GaAs grown at higher temperatures. Among the interesting properties of these buffer layers are reduced recombination times and high breakdown voltages useful in power field effect transistors (FETs). We have used TEM, in conjunction with double crystal x-ray rocking curves, in studying GaAs grown and annealed at a variety of temperatures. X-ray rocking curve analysis has separated LT (low temperature) GaAs growth into three ranges of growth temperature: the “low-range” below 215°C, the “mid-range” from 215 to 340°C, and the “high-range” above 340°C. The low-range material is amorphous, as suggested by the presence of only the bulk reflections in the x-ray diffractometei profile and from HRTEM images of the MBE-grown buffer layer. The mid-range is single crystal and defect-free, although larger in lattice parameter than stoichiometric GaAs by as much as 0.08%.
