Determination and modeling of the optical constants of direct band gap Be_xZn_(1-x)Te grown by molecular beam epitaxy

摘要

The optical constants ε(E) of direct band gap Be_xZn_(1-x)Te have been measured at 300 K using spectral ellipsometry (0.73-6.45 eV). The ε(E) spectra displayed distinct structures associated with critical points at E_0, E_0+Δ_0, E_1, E_1+Δ_1, e_1+Δ_1 and E_2. The experimental data over the entire measured spectral range has been fit using the Holden-Munoz model dielectric function, which is based on the electronic energy-band structure near critical points plus excitonic and band-to-band Coulomb-enhancement effects at E_0, E_0+Δ_0 and the E_1, E_1+Δ_1, doublet. In addition to evaluate the energies of these various band-to-band critical points, information about the binding energy (R_1) of the two-dimensional exciton related to the E_1, E_1+Δ_1 critical points was obtained. The value of R_1 was in good agreement with effective mass theory. The ability to evaluate R_1 has important ramifications for first-principles band-structure calculations that include exciton effects at E_0, E_1, and E_2.