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 temperatures (LT-GaAs). The intensity of forbidden Raman scattering of longitudinal optical and transverse optical phonons linearly increases as a function of the concentration of excess As in the range of [As-Ga] = 0.04 x 10(20)-1.175 x 10(20) cm(-3). 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 layers is explained as the strain induced by As-Ga (As antisite)-related defects with low structural symmetry. (C) 2000 American Institute of Physics. [S0021-8979(00)10819-9].