Optical properties of Zn_1-xCd_xSe epilayers grown on (100) GaAs by molecular beam epitaxy

Zn_1-xCd_xSe epilayers were grown on (100) GaAs substrates by molecular beam epitaxy. Lattice constants of the epilayers were measured by (004) rocking curve X-ray diffraction. A full width at half maximum of 475 to 2100 arcsec was obtained. The dependence of the energy gap on temperature, measured by the photoluminescence (PL) spectra, was fitted by Varshni's [Y. P. Varshni: Physica 34 149 (1967)] and O'Donnell's [R. P. O'Donnell and X. Chen: Appl. Phys. Lett. 58 2924 (1991)] models. The fitting parameters β (161K to 368 K) and (hv) (13 meV to 24 meV), related to phonon energy, were obtained from Varshni and O'Donnell fits, respectively. The activation energies calculated from the integrated PL intensity versus inverse temperature decrease as the Cd content increases. The broadening of the PL linewidth with temperature was fitted by ΓT(T) = Γ₀ + Γ + Γ_aT + Γ_Lo1/ [exp(ℏω_Lo1/kT)-1]+Γ_Lo2/ [exp(ℏω_Lo2/kT)-1]+Γ_iexp(-<E _b>/kT)/. The impurity binding energy, <E_b>, was found to decrease as the Cd composition increases.