CHARACTERIZATION OF GAAS GA1-XALXAS MULTILAYER SYSTEMS BY INFRARED-SPECTROSCOPY AT NORMAL INCIDENCE/

We present experimental infrared reflectivity spectra, at normal incid ence and room temperature of two thin-film heterostructures based on G aAs, AlAs and Ga1-xAlxAs. We have generated very satisfactory fits to these spectra by using a standard technique based on optical impedance mismatch. The fit yields both electrical and structural parameters. T he latter include the composition concentration, x, and the layer thic knesses. It is demonstrated that the sensitivity of the layer thicknes s determination is greatly increased by extending the measurements int o the mid-infrared, even in the case of two comparably-sized and adjac ent layers. For very thin layers (0.03 mum) the thickness can be deter mined from the amplitude of the fringes in the mid-infrared spectrum.