Effect of temperature on isotopic mass dependence of excitonic band gaps in semiconductors: ZnO

摘要

The temperature dependence of the A, B, and C excitons of ZnO, observed in modulated reflectivity spectra of ~(68)Zn ~(18)O and ~(nat)Zn ~(nat)O in the range 10-400 K, reveal the superposition of band-gap renormalization originating in electron-phonon interaction and volume changes associated with thermal expansion and (or) isotopic composition in combination with anharmonicity. At low temperatures, the A, B, and C excitons in natural ZnO reach limiting values depressed from their values for the infinitely massive isotopes (the latter are free from electron-phonon interaction and anharmonicity). The C excitons of ~(68)Zn ~(18)O and ~(nat)Zn ~(nat)O converge with increasing temperature, demonstrating the independence of the band gap from isotopic mass at high temperatures.