We report on the photocurrent behavior of single GaN n-i-n nanowires (NWs) grown by plasma-assisted molecular-beam epitaxy on Si(111). These structures present a photoconductive gain in the range of 10(5)-10(8) and an ultraviolet (350 nm) to visible (450 nm) responsivity ratio larger than 6 orders of magnitude. Polarized light couples with the NW geometry with a maximum photoresponse for polarization along the NW axis. The photocurrent scales sublinearly with optical power, following a I ~ P(β) law (β < 1) in the measured range with β increasing with the measuring frequency. The photocurrent time response remains in the millisecond range, which is in contrast to the persistent (hours) photoconductivity effects observed in two-dimensional photoconductors. The photocurrent is independent of the measuring atmosphere, either in the air or in vacuum. Results are interpreted taking into account the effect of surface states and the total depletion of the NW intrinsic region.

The structural and optical properties of InGaN/GaN nanowire heterostructures grown by plasma-assisted molecular beam epitaxy have been studied using a combination of transmission electron microscopy, electron tomography and photoluminescence spectroscopy. It is found that, depending on In content, the strain relaxation of InGaN may be elastic or plastic. Elastic relaxation results in a pronounced radial In content gradient. Plastic relaxation is associated with the formation of misfit dislocations at the InGaN/GaN interface or with cracks in the InGaN nanowire section. In all cases, a GaN shell was formed around the InGaN core, which is assigned to differences in In and Ga diffusion mean free paths.