Band-edge photoluminescence in polycrystalline ZnO films at 1.7 K

This paper presents an investigation of the low-temperature band-edge photoluminescence (PL) of ZnO films prepared by spray pyrolysis. Annealing samples in forming gas modified the PL spectra and density of conduction electrons. Photoluminescence revealed a complicated multi-line structure. The origin of the observed near-UV lines was identified in terms of bound exciton complexes and the phonon replicas. In annealed high-conductivity samples this was the usual optical phonon replica with a period of 71.6 meV. In low-conductive as-grown films an oscillating structure with a period of 108 meV was revealed. This new structure was attributed to a two transverse optical phonon replica.