Optical Properties of Al1As.

We report pseudodielectric function, (epsilon), data for Al1As alloys of target compositions x=0.00 through 0.80 in steps of 0.10 grown by liquid phase epitaxy and measured by spectroellipsometry. Cleaning procedures that produce abrupt interfaces between the technologically relevant alloys x = 0.6 the peak data appear to show systematic discrepancies indicating that chemical cleaning cannot completely remove surface overlayers for high- Al-content samples. Optical measurements for a sample with x = 0.9 also reveal that oxidation of high-Al samples proceeds irregularly and not along a uniform spatial front. We also discuss interpolation procedures to obtain approximate representations of dielectric function spectra at compositions other than those measured and give suggestions for improving accuracy in future optical measurements on these and related materials. *Bell Communications Research, Inc., Murray Hill, NJ 07974 **Xerox Palo Alto Research Center, Palo Alto, CA 94304