Optical functions of AlAsSb characterized by spectroscopic ellipsometry

Nominally undoped AlAsxSb1-x layers with a thickness of 200 nm to 370 nm and arsenic mole fraction x of 0.325-0.872 were grown on Fe-doped (001) InP substrates by solid-source molecular beam epitaxy. Their optical properties were investigated over a wide photon range of 0.7 eV to 5 eV at room temperature using variable angle spectroscopic ellipsometry. The obtained data were analyzed using standard multilayer calculation schemes. The determined thicknesses of these layers were in good agreement with the calibrated normal growth rate. For photon energies below the AlAsSb band gap, which is the transparency region of the AlAsSb layer, pronounced Fabry-Perot interference oscillations due to the multiple internal reflections in the AlAsSb layer were observed. A clear blue shift of the energy gap of AlAsSb was observed as the As concentration increased. The refractive index decreased with an increase of the bandgap energy in the energy range of 0.7 eV to 2.1 eV. This trend is the same as that observed in conventional III-V alloy semiconductors. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.