DIELECTRIC FUNCTION OF GAAS/ALAS SUPERLATTICES GROWN ON GAAS SUBSTRATES WITH DIFFERENT ORIENTATION

We performed spectroellipsometric measurements on (GaAs)n/(AlAs)m superlattices grown on GaAs substrates with (100), (110), (111) and (120) orientations. From the second derivatives of the real and imaginary parts of the pseudodielectric function we deduced that the GaAs and AlAs components appear in these spectra as well as a ''superlattice transition''. The critical point energies E1, E1 + DELTA1, and E0' of the GaAs components increase with decreasing n (a confinement effect) and E2(SIGMA) is n independent while E0, E1, E0 and E2 of AlAs do not depend on m within the experimental accuracy.