Role of excitons in the excitation of deep-level emission in ZnO crystals

In undoped ZnO crystals, photoluminescence excitation (PLE) spectra of deep‐level green and orange PL bands as well as photocurrent (PC) spectra were measured at 77 and 290 K. Some PLE and PC peaks whose energy positions coincided with that of free exciton and its excited states were observed, the intensity of PL and PC excited in these peaks being higher than under excitation by band‐to‐band light. At the same time, a sharp minimum was found in PLE and PC spectra at the position of donor‐bound exciton. Obtained results were accounted for by the interaction of excitons with lattice defects. A number of longer wavelength PLE and PC peaks whose energy positions coincided in fact with that of the first, second and third phonon replicas of free exciton were also observed. The origin of these peaks is discussed. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)