DEFECTS IN MOLECULAR-BEAM EPITAXIAL GAAS GROWN AT LOW-TEMPERATURES

We have utilized a variable energy positron beam and infrared transmis sion spectroscopy to study defects in GaAs epilayers grown at low temp eratures (LT-GaAs) by molecular beam epitaxy. We have measured the Dop pler broadening of the positron-electron annihilation gamma ray spectr a as a function of positron implantation energy. From these measuremen ts, we have obtained results for the depth profiles of Ga monovacancie s in unannealed LT-GaAs and Ga monovacancies and arsenic cluster relat ed defects in annealed LT-Ga-As. We have also studied the effects of t he Si impurities in annealed LT-GaAs. The infrared transmission measur ements on unannealed LT-GaAs furnish a broad defect band, related to A s antisites, centered at 0.370 eV below the conduction band.