Temperature dependent band gap and homogeneous line broadening of the exciton emission in ZnO

We report on an experimental study of the temperature dependent band gap shift and the homogeneous line broadening of the excitonic luminescence in ZnO. This data is derived from photoluminescence (PL) measurements at temperatures from T = 10–290 K and fitting the PL line shape with a theoretical model for the exciton line and its LO-phonon replica. Additionally, transmission measurements are utilized to extend the data of the temperature dependent band gap into the temperature range from 290 K up to 800 K. The experimentally determined shift is compared with one that is obtained numerically from the phonon density of states, the pressure dependent band gap, the thermal expansion coefficient and the bulk modulus with only a single fit parameter. The interaction of excitons with phonons leads to a homogeneous broadening of the excitonic emission which reaches values of 40 meV at room temperature. This mechanism results in a substantially increased threshold for stimulated emission from every process involving excitons. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)