Electrical characterization of single GaN nanowires

In this paper a statistically significant study of 1096 individual GaN nanowire (NW) devices is presented. We have correlated the effects of changing growth parameters for hot-wall chemically-vapour-deposited (HW-CVD) NWs fabricated via the vapour-liquid-solid mechanism. We first describe an optical lithographic method for creating Ohmic contacts to NW field effect transistors with both top and bottom electrostatic gates to characterize carrier density and mobility. Multiprobe measurements show that carrier modulation occurs in the channel and is not a contact effect. We then show that NW fabrication runs with nominally identical growth parameters yield similar electrical results across sample populations of > 50 devices. By systematically altering the growth parameters we were able to decrease the average carrier concentration for these as-grown GaN NWs similar to 10-fold, from 2.29 x 10(20) to 2.45 x 10(19) cm(-3), and successfully elucidate the parameters that exert the strongest influence on wire quality. Furthermore. this study shows that nitrogen vacancies, and not oxygen impurities, are the dominant intrinsic dopant in HW-CVD GaN NWs.