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ZnO/Zn/Al"2O"3 sandwich structures are grown on glass substrates by magnetron sputtering. The effect of Al"2O"3 layers on optical properties of ZnO/Zn/Al"2O"3 sandwich structures is investigated. Results indicated that as the deposition time of Al"2O"3 increases, violet peak centered at 402nm gradually shifted to 412nm and the intensity firstly decreases and then increases. We discuss the intensity change and shift of violet peak relating to V"Z"n defects and the band alignment of ZnO/Zn/Al"2O"3 sandwich structures, respectively. We proposed that ZnO/Zn/Al"2O"3 sandwich structures can be approximately regarded as a quasiquantum-well-like structure. So the electron tunneling from Zn to Al"2O"3 layer is suppressed and the photogenerated carriers can be confined in the Zn Fermi level. In order to further understand the effect of posttreatment on optical properties of samples, samples are annealed in vacuum at 350^oC for 1h. PL emissions are weakened with the increase of Al"2O"3 deposition time. Interestingly, at a same deposition condition, PL emissions are still improved after posttreatment. Combined Al"2O"3 layer modulation with annealing treatment, steady PL properties can be effectively improved.
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