High-Aspect-Ratio GaN p-i-n Nanowires for Linear UV Photodetectors

Ultraviolet GaN photodetectors based on nanowires (NWs)fabricatedby top-down strategies promise improved uniformity, morphology, anddoping control with respect to bottom-up ones. However, exploitingthe advantages of the NW geometry requires sub-wavelength NW diameters.We present fabrication of large-area sub-200 nm diameter top-downGaN p-i-n NW ultraviolet photodetectors with lengths over 2 & mu;m producedfrom a planar specimen using nanosphere lithography, followed by acombination of dry and crystallographic-selective wet etching. Photocurrentmeasurements in single-NW devices under bias show a linear responseas a function of the optical power, with increased current levelsunder reverse bias. The linearity proves that the drift of photogeneratedcarriers at the junction is the dominating photodetection mechanism,with negligible contributions from surface effects. These resultsdemonstrate that the unique properties of NW-based photodetectorscan be assessed through a scalable and low-cost fabrication process.