Optical constants and critical-point parameters of GaAs1–xSbx alloy films grown on GaAs



Spectroscopic Ellipsometry (SE) is used in this work to investigate the optical properties of the GaAs1–xSbx alloys. The present study is based on a set of GaAs1–xSbx layers (x = 0.0%, 6.7% and 10.8%) grown on GaAs substrate by molecular beam epitaxy (MBE). The SE measurements were carried out in the energy range of 1.4 – 5.5 eV at room temperature for 70° and 75° incident angles, before and after chemical etching. The optical constants of GaAs1–xSbx alloys were extracted using the Newton–Raphson method based on the four-phase model (ambient – GaAs native oxide overlayer – GaAs1–xSbx film – GaAs substrate). Analytic line shapes fitted to numerically calculated second derivatives of the dielectric functions determined the critical-points parameters above the GaAs1–xSbx bandgap E0. The best fit parameters and the experimental extracted data show in particular a red-shift and a broadening increase of E1, E1 + Δ1, E0 and E2 transitions by increasing Sb content. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)