Metal-free doping process to enhance the conductivity of zinc oxide nanorods retaining the transparency.

The well-ordered metal oxide nanostructures can be synthesized successfully, but the conductance of these structures is limited, which is a disadvantage for applying these in photovoltaic and display devices. Conductivity of a semiconductor can be improved by using metal doping, but the issue becomes a major challenge in nanostructures since their high surface energy usually hinders any metal doping process. Here we show an entirely new metal-free doping strategy to enhance the current conduction of ZnO nanorods' (NRs) arrays through a sulphidation technique. The process is based on the electronegativity difference between S and O because of which one can expect a rigorous bond rearrangement at the interface and a ZnOS-ZnS composite is formed as O is being partially replaced by S. The current conduction by the metal oxide NRs arrays is significantly enhanced by nearly 4 orders of magnitude without sacrificing the transparency of the NRs arrays. The increased current conduction is assigned due to an increase in the Zn(i) concentration as evidenced from the electron paramagnetic resonance measurements. The composite layer grown on p-Si forms a photodiode which is highly sensitive to visible light with a very fast response time.