Abstract
We have investigated the microstructure and photoluminescent properties of Zn 1− x Co x O ( x ≤ 0.377) films deposited on (0 0 1)-oriented Al 2O 3 substrates using radio-frequency magnetron sputtering. A single phase with a wurtzite-like structure was found in Zn 1− x Co x O films with x up to 0.105. However, a small amount of Co 3O 4 clusters could be observed when the doping level x reached 0.313. The PL spectra showed that Co doping in ZnO films would suppress near band edge (NBE) and violet emissions due to the degradation of material quality and the increase of nonradiative centers. For Zn 1− x Co x O films with higher Co concentration ( x = 0.313 and 0.377, respectively), a broad intense emission band centered at 332 nm (deep ultraviolet emission) was observed. The intense deep ultraviolet emission should be related to the O 2− → Co 2+ charge-transfer process in clusters Co 3O 4 embedded in Zn 1− x Co x O films.
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