Optical constants and critical-point parameters of GaAs_(1-x)Sb_x alloy films grown on GaAs

摘要

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 rnin the energy range of 1.4-5.5 eV at room temperature for rn70° and 75° incident angles, before and after chemical etching. The optical constants of GaAs_(1-x)Sb_x alloys were extracted using rnthe 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.