Reduced Graphene Oxide-Nanostructured Silicon Photosensors with High Photoresponsivity at Room Temperature

We have created nanostructured Si (∼3 nm) with a direct band gap of 1.37 eV on electrically conducting reduced graphene oxide (rGO) for a highly efficient photosensor. This robust photosensor is fabricated using a nonequilibrium processing route, where nanosecond excimer laser pulses melt the alternating layers of Si and amorphous carbon to form micropillars and nanoreceptors of Si on rGO layers. The incident white light generates free carriers in the Si microstructures and nanoreceptors which are ballistically transported (via rGO layers) to the external circuit under the application of a voltage bias. The responsivity of rGO-Si devices to light (resistance vs time) and I–V measurements indicate an exponential drop in resistance with the incidence of white light and nonrectifying nature, respectively. Photoresponsivity of the rGO-Si devices is calculated to be 3.55 A/W at room temperature, which is significantly larger than the previously fabricated graphene-based ohmic photosensors. Temperature-dependent resistance measurements of rGO-Si structures follow Efros–Shklovoskii variable range hopping (ES-VRH) electrical conduction in the low-temperature region (<100 K) and Arrhenius conduction in the high-temperature region (>100 K). In rGO, the localization length, hopping energy, and activation energy are calculated to be 17.58 μm, 3.15 meV, and 1.67 meV, respectively. The 2D nature of highly reduced and less defective rGO also render an interesting negative magnetoresistance (∼2.5%) at 5 K, thereby indicating potential implications of rGO-Si in optospintronics. The large-area integration of rGO-Si structures with sapphire employing nanosecond pulsed laser annealing and their exciting photosensing properties will open a new frontier for further extensive research in these functionalized 2D materials.