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

We present experimental infrared reflectivity spectra, at normal incidence and room temperature of two thin-film heterostructures based on GaAs, 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. The latter include the composition concentration, x, and the layer thicknesses. It is demonstrated that the sensitivity of the layer thickness determination is greatly increased by extending the measurements into the mid-infrared, even in the case of two comparably-sized and adjacent layers. For very thin layers (0.03 mum) the thickness can be determined from the amplitude of the fringes in the mid-infrared spectrum.