Modelling the optical constants of Si_xGe_1-x alloys in the range 1.7-5.6 eV

摘要

Optical constants of Si_xGe_1-x alloys are modelled over the spectral range from 0.7 eV to 5.6 eV for all compositions 0 ≤ x ≤ 1. The employed model is the modified Adachi's model, which utilizes variable line broadening instead of the conventional Lorentzian one. The model takes into account transitions at the indirect band gap E_g~id, and critical points E_0, E_0 + Δ_0, E_l, E_1 + Δ_1, E_0, E_2(X), and E_2 (∑). Excitonic effects are not considered. The model parameters are determined using a global optimization routine, namely an acceptance-probability-controlle simulated annealing algorithm. Excellent agreement with the experimental data is obtained in the entire investigated energy and composition ranges. The obtained relative root mean square errors are below 4.5/100 and 6.5/100 for the real and imaginary parts of the index of refraction, respectively.