CHARACTERIZATION OF THIN BUFFER LAYERS FOR STRONGLY MISMATCHED HETEROEPITAXY

Thin buffer layers for strongly mismatched heteroepitaxy of GaAs and I nP on Si were investigated with respect to their structural characteri stics in a scanning electron microscope (SEM). A novel technique, whic h is based on energy-dispersive X-ray spectrometry (EDX), was utilized for thickness measurement. With GaAs thicknesses were determined in t he range from several mu m down to 10 nm. Their accuracy was confirmed by mechanical surface tracing of selectively etched steps. The crysta l quality of the thin layers was probed by electron-channelling patter ns (ECP). We found a dependence on buffer-layer thicknesses which was confirmed by spectroscopic ellipsometry. For thin layers the optical a bsorption coefficient near the band edge, which is a measure of the de nsity of structural defects in thin layers, showed the smallest deviat ion from the bulk standard. Furthermore, the buffer-layer quality dete rmined by ECP was correlated with the surface morphology and with the density of twin defects in subsequently grown thick main layers of GaA s and InP, respectively. We conclude that EDX and ECP are powerful met hods for the structural characterization of thin buffer layers playing a key role in mismatched heteroepitaxy. Both techniques were performe d in a SEM, which is a standard tool in research and development as we ll as in industrial laboratories.