Applicability of ZnO single crystals for ultraviolet sensors

Photoconductivity of ZnO single crystals grown by a hydrothermal method for ultraviolet light was measured. The ZnO single crystals have photo response in a range of wavelengths shorter than 380 nm. O‐faces of ZnO single crystals of the c ‐plane showed higher photocurrents and wider spectral response than did Zn‐faces. It is thought that band bending at the surface regions of ZnO crystals is large at the O‐face but small at the Zn‐face, because the surface state density for electron capture at the O‐face was higher than that of the Zn‐face and, therefore, carriers generated at the surface region by UV light were effectively separated at the O‐face region before their recombination. The difference between photoresponces of the O‐face and the Zn‐face is also useful for determining the polarity of a ZnO crystal. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)