Effect of Zn doping on ultraviolet emission of ZnO crystals

ZnO single crystal wafers were treated in Zn-rich ambient at a high temperature. It is found that the UV intensity of the Zn-treated samples is dramatically enhanced both at low temperature (10?K) and at room temperature compared with the as-grown ZnO crystals. It is also observed that the peak energy in the visible range shifts from 2.35 to 2.48?eV. It is suggested that Zn interstitial is the donor coupling with neutral-donor-bound excitons (D0X). This donor augments the emission intensity of D0X and its two-electron satellites at low temperature. The enhancement of UV emission at room temperature should result from a new mechanism which involves coupling of free excitons and donor Zni. The shift of the visible emission peak may originate from zinc antisite (Zno). The Hall measurements support these arguments.