Length-Dependent Photoelectric Property of ZnO Nanowires

An interesting phenomenon that the photocurrent (the difference between illumination and dark current) of a ZnO nanowire (NW) under a specified voltage increased as its length increased in a certain range was observed previously and it was supposed to be mainly due to a special mean free path effect (MFPE) which caused a special distribution of dark electron density along the length with two higher electron density regions near the two ends of the NW, respectively, and the lower one in the middle part. However, such an explanation would be unreasonable and the true reasons should be the growing-process caused variation of the oxygen adsorption capacity along the NW length and the length-dependent lifetime of photogenerated carriers. Based on this understanding, a theoretical model to properly explain this phenomenon is proposed and the calculation results are in good agreement with the experimental data. This work has introduced an improved insight into the theory of the length-dependent photoelectric property of ZnO NWs.