PHOTOREFLECTANCE CHARACTERIZATION OF OMVPE GAAS ON SI

Photoreflectance, a contactless, non-destructive optical characterization tool, can be of great utility to the material scientist in identifying crystal growth problems and ascertaining material quality in a very short time. It provides a precise measurement of the spectral energy of the fundamental absorption edge and higher lying critical point transitions. Shifts in these energies are a measure of the built-in strain in strain-layered heterostructures. Moreover, the spectral energy of the so-called Franz-Keldysh oscillation extrema is directly related to the net carrier concentration of the semiconductor material under study. We have used the Photoreflectance technique to determine the crystal quality, the carrier concentration, and the built-in strain of epitaxial GaAs grown by OMPVE on Si substrates. The study includes determination of these parameters as a function of various growth conditions, post-growth anneal cycle, and spot position on the wafer. Results are correlated with X-ray diffraction, and C-V measurements.