Direct laser writing of vertical junctions in graphene oxide films for broad spectral position-sensitive detectors

Heterostructures with built-in electric fields are crucial for charge separation and lateral photovoltaic effect in current position-sensitive detectors (PSDs), which have to be produced by combining semiconductors with metal or other semiconductors to form various vertical junctions (e.g. Schottky junctions) via complicated and high-cost manufacture processes. In the present work, it was found that vertical junctions can be directly written and patterned inside graphene oxide (GO) films with gradient C/O ratios by laser scribing due to the optical filter effect of the films and the formation of reduced GO (rGO) layers. Such junctions were verified to show the capability for high-precision position sensing on the micrometer scale, owing to the lateral photovoltaic effect. These self-powered laser-scribed PSDs can exhibit a small nonlinearity of <5.4%, which is far less than the acceptable level of 15%. A fast response time of about 1 ms can be obtained under a zero bias voltage, which is the fastest speed among the photodetectors based on pure rGO. Electron lateral diffusion in the upper layers of the laser-scribed devices was found to play a main role. These suggest that laser-scribed vertical junctions inside rGO are promising for high-precision displacement sensing, with the capability of low cost, flexibility, and passive operation mode.