SPECTROSCOPIC CHARACTERIZATION OF LOW-TEMPERATURE-GROWN GAAS EPITAXIAL-FILMS

Femtosecond time-resolved reflectance and Raman scattering studies hav e been made on GaAs epitaxial layers grown at temperatures between 200 and 300 degrees C and subsequently annealed. A subpicosecond carrier lifetime (similar to 0.25 ps) has been measured for a sample grown at 250 degrees C and annealed at 600 degrees C. Raman measurements using a back scattering geometry show a strong TO phonon band for samples gr own at 200 degrees C and 250 degrees C, while it is absent for samples grown at 275 and 300 degrees C. The band width of the LO band increas es with decreasing growth temperature. A phonon band corresponding to As precipitates is also observed at 200 cm(-1) for samples grown at 20 0 and 250 degrees C. A strong correlation is found between the measure d carrier lifetime and Raman profile.