Raman scattering study of GaAs crystalline layers grown by molecular beam epitaxy at low temperature

Raman scattering, x-ray diffraction, and transmission electron microscopy (TEM) were used to study GaAs layers grown by molecular beam epitaxy at low substrate temperature (LT-GaAs). The intensity of forbidden Raman scattering of longitudinal optical and transverse optical phonons linearly increase as a function of the concentration of excess As in the range of [As_]=0.04×10^－1.175×10^cm^. Concentrations of excess As in LT-GaAs layers were estimated from the lattice spacings measured with an x-ray diffractometer. No obvious defect was seen in cross-sectional TEM images of these nonstoichiometric As-rich GaAs layers. The origin of the forbidden Raman scattering of the nonstoichiometric LT-GaAs layer is explained as the strain induced by As_ (As antisite)-related defects with low structural symmetry