Photoconductive study and carrier dynamicsof vertically aligned GaAs nanowires

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