Burstein-Moss effect in n-type MBE-grown ZnSe thin films

Using ellipsometry and prism coupling, we have measured the dielectric functions of a series of Cl-doped ZnSe epilayers grown on GaAs substrates. The carrier concentrations were determined using Hall measurements for samples between $6.30 \times 10^{16}~cm^{-3}$ and $9.50 \times 10^{18}~cm^{-3}$. Variable angle spectroscopic ellipsometry in the energy range between 0.7 and 6.5~eV was used in conjunction with prism coupling to obtain the complex dielectric functions of the specimens. Upon careful examination of the dielectric functions obtained for these thin films, we find that its fundamental band gap blue shifts with respect to the carrier concentration. As our theoretical calculations indicate, the origin of this blue shift is due to the Burstein-Moss effect. The characteristics of the higher order transitions are also determined for this doped system.