Enhanced Negative Photoconductivity in InAs Nanowire Phototransistors Surface-Modified with Molecular Monolayers

Negative photoconductivity (NPC) mechanisms are widely investigated for high-performance InAs nanowire (NW) phototransistors, where these mechanisms are usually attributed to severe carrier scattering centers, light-assisted hot electron trapping in the surface oxide, and/or defects induced photogating layer. However, further insights into their photodetecting mechanisms, as well as corresponding performance enhancement of these NW phototransistors, are still very limited. This work reports the NPC behavior in surface-modified InAs NW phototransistors based on photoexcitation induced majority electron trapping in the bonded sulfur monolayer under optical illumination. In order to enhance hot electron trapping ability of the bonded sulfur layer, aromatic thiolate (ArS-)-based molecular monolayer with strong electron-withdrawing group is employed using simple wet chemistry for the surface modification of InAs NW photo-transistors. The magnitude of the photoexcitation induced hot electron trapping is increased by the stronger electron-withdrawing ability of the ArS-based molecular monolayer, enabling the hot electrons to be trapped and released more efficiently, resulting in NW phototransistors with good sensitivity, fast photoresponse, and long-term stability to low intensity visible light. These results confirm the potential of InAs NW phototransistors surface-passivated with molecular monolayers in the application and realization of high-sensitive and long-term stable room temperature nanoscale photodetectors.