Photoconductive properties of undoped and nitrogen‐doped ZnO single crystals in various ambiences

Abstract

AbstractThe effects of ambiences on photoconductive properties of the Zn‐face of undoped ZnO and nitrogen‐doped ZnO (ZnO:N) single crystals are described. Oxygen (O2) gas affected the photocurrent spectra of the Zn‐face of both single crystals. The photocurrent was smallest in O2 gas and was largest in the vacuum ambience. The influence of ambience was very small in the visible light region but was large in the UV region. Regardless of the ambience, photocurrent of the Zn‐face of ZnO:N showed no sensitivity in the visible region. The decay time response of undoped ZnO and ZnO:N single crystals was also affected by the ambience. Decay time responses of both single crystals were fastest in O2 gas and were slowest in the vacuum ambience. The decay time response of the ZnO:N single crystal was faster than that of the undoped ZnO single crystal. These results showed that the effect of oxygen‐mediated surface recombination is strong in both large single crystals with very small surface‐to‐volume ratio and no grain boundary effect. The results also showed that doped nitrogen decreases the density of electron and hole traps near the surface region of the crystals. It is thought that steepness of band bending near the surface of a ZnO:N single crystal is smaller than that of an undoped ZnO single crystal. In conclusion, the Zn‐face of a ZnO:N single crystal sealed with O2 gas is useful as a photoconductive type UV sensor. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)