Studies of photoconductivity and field effect transistor behavior in examining drift mobility, surface depletion, and transient effects in Si-doped GaN nanowires in vacuum and air

Variable intensity photoconductivity (PC) performed under vacuum at 325 nm was used to estimate drift mobility (μ) and density (σs) of negative surface charge for c-axis oriented Si-doped GaN nanowires (NWs). In this approach, we assumed that σs was responsible for the equilibrium surface band bending (∅) and surface depletion in the absence of illumination. The NWs were grown by molecular beam epitaxy to a length of approximately 10 μm and exhibited negligible taper. The free carrier concentration (N) was separately measured using Raman scattering which yielded N = (2.5 ± 0.3)  × 1017 cm−3 for the growth batch studied under 325 nm excitation. Saturation of the PC was interpreted as a flatband condition whereby ∅ was eliminated via the injection of photogenerated holes. Measurements of dark and saturated photocurrents, N, NW dimensions, and dimensional uncertainties, were used as input to a temperature-dependent cylindrical Poisson equation based model, yielding σs in the range of (3.5 to 7.5) × 1011 cm−2...