Nanowires (NWs) with radial p‐i‐n junction have advantages, such as large junction area and small influence from the surface states, which can lead to highly efficient material use and good device quantum efficiency. However, it is difficult to make high‐quality core–shell NW devices, especially single NW devices. Here, the key factors during the growth and fabrication process that influence the quality of single core–shell p‐i‐n NW devices are studied using GaAs(P) NW photovoltaics as an example. By p‐doping and annealing, good ohmic contact is achieved on NWs with a diameter as small as 50–60 nm. Single NW photovoltaics are subsequently developed and a record fill factor of 80.5% is shown. These results bring valuable information for making single NW devices, which can further benefit the development of high‐density integration circuits.

Nitrogen-doped p-type zinc oxide (p-ZnO:N) thin films were fabricated on a-/c-plane sapphire (a-/c-Al2O3) by plasma-assisted molecular beam epitaxy. Hall-effect measurements show that the p-type ZnO:N on c-Al2O3 degenerated into n-type after a preservation time; however, the one grown on a-Al2O3 showed good stability. The conversion of conductivity in the one grown on c-Al2O3 ascribed to the faster disappearance of NO and the growing N2(O), which is demonstrated by x-ray photoelectron spectroscopy (XPS). Compressive stress, caused by lattice misfit, was revealed by Raman spectra and optical absorption spectra, and it was regarded as the root of the instability in ZnO:N.

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We report on InP-based metamorphic In0.83Ga0.17As photodetectors with dramatically suppressed dark currents by inserting a strain-compensated In0.66Ga0.34As/InAs superlattice electron barrier in the In0.83Ga0.17As absorption layer. Compared with a reference detector without the barrier, the device showed that the dark current is reduced by about half at room temperature and is more than two orders of magnitude at 77 K at low bias, while the responsivity remained unchanged. The generation recombination and tunneling currents are significantly suppressed, and the dark current remains diffusion-current-limited above 175 K. The dark current density at −10 mV is reduced to 3.95 nA/cm2 at 175 K.