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 (E) of direct band gap BexZn1-xTe have been measured at 300 K using spectral ellipsometry (0.73-6.45 eV). The (E) spectra displayed distinct structures associated with critical points at E0, E0+0, E1, E1+1, 1+1 and E2. The experimental data over the entire measured spectral range has been fit using the Holden-Mu?oz 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 E0, E0+0 and the E1, E1+1, doublet. In addition to evaluate the energies of these various band-to-band critical points, information about the binding energy (R1) of the two-dimensional exciton related to the E1, E1+1 critical points was obtained. The value of R1 was in good agreement with effective mass theory. The ability to evaluate R1 has important ramifications for first-principles band-structure calculations that include exciton effects at E0, E1, and E2.