CHARACTERIZATION OF GAAS HETEROLAYERS BY MICRO-RAMAN SPECTROSCOPY

GaAs heterolayers on (100) InAs and InP substrates were characterized by micro-Raman spectroscopy. The layers were 2 mu m thick and grown by molecular beam epitaxy at 480 degrees C. A bevel was formed an each s ample, and Raman scattering from the exposed interface region was coll ected. In close vicinity to the GaAs/InAs interface, the frequency of the GaAs longitudinal-optical (LO) phonon was lower by about 3 cm(-1) than at the as-grown surface. The LO shift decreased with increasing d istance from the interface, but a small shift (about 0.5 cm-l) was sti ll observed even at distances larger than 0.2 mu m. The shift was beli eved to be due to residual misfit strain, and the value of biaxial str ain was estimated to be about 0.6% at the interface. Almost the same r esults were obtained for GaAs/InP, where the mismatch degree is smalle r by a factor of two than in GaAs/InAs. This would indicate that the r esidual strain in a thick heterolayer depends little on the initial mi sfit degree.