Abstract
Highly dense, vertically aligned silicon nanowires (SiNWs), having diameters in the range of 40-100nm and length upto 5 mu m, are grown by metal assisted chemical etching technique on p-type polycrystalline silicon (pc-Si) substrate. The hetero-junction photodiodes, for ultraviolet sensing application, are fabricated by depositing tin oxide (n-SnO2) onto pc-Si and SiNWs on pc-Si surface, using simple and low cost electrochemical deposition technique. The prepared SiNWs and n-SnO2 decorated SiNWs are examined by scanning electron microscopy and elemental dispersive analysis by X-ray. Three photodiodes with device architectures Al/Ti/SiNWs/pc-Si/Ti/Al, Al/Ti/n-SnO2/pc-Si/Ti/Al and Al/Ti/n-SnO2/SiNWs/pc-Si/Ti/Al are fabricated and their UV sensing behavior is studied by recording their V-I characteristics under dark and UV-radiation. The recorded V-I curves of the fabricated devices show diode like behavior and their rectification ratio, turn on voltage, effective barrier height and sensitivity are calculated and compared. Under UV exposure, the V-I studies under forward and reverse biasing for the device Al/Ti/n-SnO2/SiNWs/pc-Si/Ti/Al shows significantly higher rectification ratio, sensitivity, responsivity and detectivity around 172.3 at +/- 9V, 64, 0.3456A/W at 5V and 8.02869x10(12) Jones respectively. Further, the photo-resistive measurements of the device also show its excellent reproducible nature. This better UV sensing behavior is also supported with proposed UV sensing mechanism under biasing conditions.