Persistent photoconductivity in Al-doped ZnO photoconductors under air, nitrogen and oxygen ambiance: Role of oxygen vacancies induced DX centers

摘要

Here we report the synthesis and fabrication of ZnO photoconductors with high transparency, high performance and low cost upon Al doping (3, 5, 7 wt. %) into the ZnO lattice. The incorporation of Al into the ZnO lattice significantly changed the structural, morphological and optical properties of the thin films. The transient photoconductivity response was studied for all the samples under different ambient conditions such as in vacuum, air, nitrogen and oxygen mediums to understand the mechanism of response/recovery behavior. Under the termination of UV light, photodetectors recover via recombination of electron-hole pairs. Meanwhile, some carriers are deeply trapped at the recombination center due to the presence of deep level defects that hold the dark current value at a higher level, and persistent photoconductivity exists. A significant difference between pure and Al-doped ZnO photoconductivity behaviors have been observed in different ambient conditions. Furthermore, as compared with pure ZnO photoconductor, the photoresponse has been increased by 25 times. The responsivity was obtained to be similar to 23 times higher than that of the pure ZnO, and the maximum LDR of 85 dB has been reported upon 5 wt. % Al doping.