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 = 0.5 and the ambient are described. The ([EQ] epsilon sub 2 [EN]) data are corrected near the fundamental direct absorption edge by a Kramers-Kronig analysis of the ([EQ] epsilon sub 1 [EN]) data to circumvent a limitation of the rotating-analyzer ellipsometeric technique. The results and the associated optical functions (n), (R), and (alpha) are listed in tabular form. Accurate values of the [EQ] E sub 0 [EN] and [EQ] E sub 1 [EN] threshold energies are determined from these spectra by Fourier methods. From these values and from similar values for a GaAs- capped AlAs sample grown by organometallic chemical vapor deposition, the dependences of the [EQ] E sub 0 [EN] and [EQ] E sub 1 [EN] interband critical point energies on nominal composition are obtained. Cubic polynomial representations of these dependences are determined to allow nominal Al fractions to be calculated analytically from optical threshold data. The systematic behavior of [EQ] ( epsilon sub 1 )[EN] at 1.5 eV and of the [EQ] E sub 2 [EN] peak in [EQ] ( epsilon sub 2 ) [EN] near 5 eV show that scatter in these data is less than 1% of the peak values of the spectra for x = 0.5. For 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