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)