Characterization of Crystallinity in Low-Temperature-Grown GaAs Layers by Raman Scattering and Time-Resolved Photoreflectance Measurements

Low-temperature-grown GaAs homo-epitaxial layers were studied by Raman scattering and time-resolved photoreflectance techniques. Raman spectral profiles, polarization properties and lifetimes of photo-induced carriers depend strongly on growth conditions and post annealing. The experimental results showed that heavily defective layers were formed in as-grown layers, while post-annealed layers were less defective and consisted of partially misoriented crystallites or polycrystals. The carrier lifetime was short and the magnitude of the optical response was small in defective layers grown at relatively low temperatures, while the optical response was increased by annealing and by increasing the growth temperature. Of the samples tested, GaAs layers grown at 200–250° C and post-annealed layers gave a lifetime of 0.3 ps with relatively high optical response.