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.