TEMPERATURE-DEPENDENCE OF THE DIELECTRIC FUNCTION AND INTERBAND CRITICAL-POINTS OF ALAS OBTAINED ON AN MBE GROWN LAYER

We have measured the dielectric function of AlAs from 95 K to 600 K in the 1.7-5.6 eV energy range using spectroscopic ellipsometry. The mea surements were performed on a approximately 400 angstrom thick layer g rown by MBE on a GaAs(001) substrate. A multilayer model was used prio r to growth to determine the optimum AlAs layer thickness (approximate ly 400 angstrom) that gives the maximum sensitivity in the region of t he E0 gap. After growth the layer was covered by an As cap layer for p rotection during transfer to our ultrahigh vacuum measurement chamber. The cap was then removed by heating the sample. Analysis of the ellip sometric data with a multilayer model allows us to obtain the dielectr ic function of AlAs in the specified energy and temperature range. The obtained results are a qualitative improvement on previous measuremen ts on GaAs-covered AlAs samples. We also performed a line shape analys is of the structures observed in the numerical second derivative of th e spectra. In this way we obtained the interband critical-point parame ters and their temperature dependence. Special emphasis is placed on t he dielectric function in the E0 region and the complex of structures observed in the E2 region.