A novel model for optical functions of GaSb

In this paper we propose an analytical expression for the complex dielectric function of semiconductors which includes both discrete and continuum exciton effects. We start from the unbroadened expression for the dielectric function based on Elliott's work [R. J. Elliott, Phys. Rev. 108 (1957) 1384], and after the introduction of broadening we obtain the expression for the complex dielectric function. The proposed analytical model accurately takes into account the excitonic effects, while it satisfies the requirements that the imaginary part of the dielectric function is an odd function of energy, and the real part of the dielectric function is an even function. We show that accurate description of broadening leads to equations for the dielectric function containing only elementary functions, with terms dependent on the exciton order m describing discrete exciton states. The proposed model has been applied to model the experimental data for the absorption edge of GaSb. We have obtained good agreement with the experiment. The agreement with experimental data can be improved further if adjustable broadening function is considered instead of a simple Lorentzian one.