  The electrical and photodiode characteristics of ensemble and single p-GaN
nanowire and n-Si heterojunction devices were studied. Ideality factor of the
single nanowire p-GaN/n-Si device was found to be about three times lower
compared to that of the ensemble nanowire device. Apart from the deep-level
traps in p-GaN nanowires, defect states due to inhomogeneity in Mg dopants in
the ensemble nanowire device are attributed to the origin of high ideality
factor. Photovoltaic mode of ensemble nanowire device showed an improvement in
the fill-factors up to 60 percent over the single nanowire device with
fill-factors up to 30 percent. Reponsivity of the single nanowire device in
photoconducting mode was found to be enhanced by five orders, at 470 nm. The
enhanced photoresponse of the single nanowire device also confirms the
photoconduction due to defect states in p-GaN nanowires.

Materials Science;Mesoscale and Nanoscale Physics