Photoconductive study and carrier dynamics of vertically aligned GaAs nanowires

Single wire devices are generally fabricated to study the electrical and photoelectric behaviors of semiconductor nanowires (NWs); however detriment or contamination can hardly be avoided during manipulation of NWs under focused ion and electron beams. This could not be a trivial factor for III-V NWs which are candidates for high efficiency solar energy harvesting and sensitive photodetection. In this study an alternative way to probe the photoconductive property of individual epitaxial GaAs NWs is presented. For the sample preparation, a uniform spin-coated layer of polymer was selected to be the supporting medium for the vertically aligned NWs structure; then the adequate thinning and polishing of the sample exposed the NW tip and also achieved the required height of NW. An external power adjustable laser was introduced as the excitation source, and the dark and photoconductive currentvoltage properties of individual NW were measured by the conductive atomic force microscopy. The typical Schottky style photoconductive behavior was observed in the vertically aligned GaAs NW, and its photoresponsivity has been found to be much higher than that of the reported for single NW photodetector. Finally, a numerical model based on the experimental setup was established to simulate the photoelectric behavior of individual NW. The minority hole lifetime has been found to dominate the photoconductive current-voltage properties of NW under the positive sample bias, and can be derived from the quantitative fitting of experimental photo-IV curves.