Centers of photosensitivity in ZnO

To reveal recombination centers responsible for ZnO UV photosensitivity, combined investigations of photoconductivity (PC) and photoluminescence (PL) spectra were performed in nominally undoped ZnO single crystals. In PL spectra, green (500 nm), orange (620 nm) and red (720 nm) bands related to deep levels were present, the greater the relative intensity of orange band the higher the photosensitivity. After removal of exciting light, PL afterglow as well as PC “tail” took place at 77 K. It was found that decay time of PC “tail” coincided with that of orange band afterglow and was essentially longer than the afterglow decay times of green and red bands. The conclusion was made that recombination centers responsible for the orange band were the centers of photosensitivity. In addition, a strong influence of electron traps on steady-state PC was shown.