Optical constants and critical‐point parameters of GaAs 1– x Sb x alloy films grown on GaAs

Spectroscopic Ellipsometry (SE) is used in this work to investigate the optical properties of the GaAs 1– x Sb x alloys. The present study is based on a set of GaAs 1– x Sb x 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 GaAs 1– x Sb x alloys were extracted using the Newton–Raphson method based on the four‐phase model (ambient – GaAs native oxide overlayer – GaAs 1– x Sb x film – GaAs substrate). Analytic line shapes fitted to numerically calculated second derivatives of the dielectric functions determined the critical‐points parameters above the GaAs 1– x Sb x bandgap E 0 . The best fit parameters and the experimental extracted data show in particular a red‐shift and a broadening increase of E 1 , E 1 + Δ 1 , E ′ 0 and E 2 transitions by increasing Sb content. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)