Nitrogen-doped ZnO/n-Si core–shell nanowire photodiode prepared by atomic layer deposition

Photodiodes made from core–shell nanowires (NWs) comprising n-type silicon (n-Si; core) and nitrogen-doped ZnO (ZnO:N; shell) were fabricated by atomic layer deposition of ZnO:N on vertically aligned Si NWs. The device properties were investigated as functions of nitrogen content of the ZnO:N shell. The electron-carrier concentration of ZnO:N was modulated by adjusting the concentration of the reactant, diluted ammonium hydroxide, from 0 to 30%. The rectification ratio and the reverse-current density of the ZnO:N/n-Si planar heterojunction were evaluated under dark condition for various NH4OH concentrations. The ZnO:N/n-Si heterojunction prepared with NH4OH 15% was found to have the lowest reverse-current density with a moderate resistivity. In order to realize an effective ZnO:N/n-Si photodiode, a ZnO:N layer prepared with 15% NH4OH was deposited on well-aligned Si nanowires. The core–shell NW photodiode showed more sensitive photodetecting performance in UV light than the planar photodiode. Also, the significantly enhanced performances of the core–shell NW photodiode were evaluated by examining its spectral responsivity.