RAMAN-STUDY OF DEFECTS IN A GAAS BUFFER LAYER GROWN BY LOW-TEMPERATURE MOLECULAR-BEAM EPITAXY

Raman scattering measurements on high-resistivity layers of GaAs grown by molecular beam epitaxy at low temperature are presented. Several defect-related features are observed, including two peaks attributed to quasi-localized vibrational modes of point defects, one with a frequency of 223 cm-1 similar to a mode previously observed in electron-irradiated GaAs, and the other with a frequency of 47 cm-1 similar to a mode observed in ion-implanted GaAs. We suggest that these are due to arsenic interstitials and gallium vacancies, respectively. We also observe peaks at 200 and 258 cm-1, which we believe may be due to vibrational modes in small clusters of arsenic. The 223 cm-1 mode is the only defect-related mode still observed after a 10-min annealing treatment at 600-degrees-C, although it is significantly broader and has different symmetry from the 223 cm-1 mode in the unannealed material. This indicates that the 223 cm-1 mode in the annealed material is due, at least in part, to a defect other than the arsenic interstitial.