Temperature dependence of the band-edge photoluminescence of films

摘要

We report a systematic investigation of band-edge photoluminescence of the diluted magnetic semiconductor alloy Zn_(1-x)Mn_xSe for a series of compositions (0 < x < 0.485). The specimens investigated were in the form of thin films fabricated by molecular beam epitaxy. The near band-edge emissions of donor-bound excitons (designated as I_2) and of neutral acceptor-bound excitons (I_1) were systematically investigated as a function of temperature and of alloy composition. These measurements also allowed us to determine the LO-phonon energy hω_(LO) = 31.2 +- 0.2 meV. From the temperature dependence of the bound exciton peak, the Varshni temperature parameter α was found to increase linearly with increasing Mn concentration x, while β decreased with x. From the temperature dependence of the full width at half maximum (FWHM) of the I_2 emission line, the broadening factors Γ(T) were determined from the fit to the data. For x > 0.20 the effect of inhomogeneous broadening Γ_(inh) on Γ(T) was found to be stronger than that of the longitudinal optical phonon term Γ_(LO). Furthermore, the activation energies of thermal quenching were obtained for both the I_2 and the I_1 peaks from the temperature dependence of the bound exciton peaks, and were found to decrease with increasing Mn concentration. Finally, we show that at high temperature the broadening of the FWHM is dominated by the LO-phonon interaction.