Focused-Laser-Enabled p-n Junctions in Graphene Field-Effect Transistors

Abstract

With its electrical carrier type as well as carrier-densities highly-sensitive to light, graphene is potentially an ideal candidate for many opto-electronic applications. Beyond the direct light-graphene interactions, indirect effects arising from induced charge traps underneath the photoactive graphene arising from light-substrate interactions must be better understood and harnessed. Here, we study the local doping effect in graphene using focused-laser irradiation, which governs the trapping and ejecting behavior of the charge trap-sites in the gate oxide. The local doping effect in graphene is manifested by a large Dirac voltage shifts and/or double Dirac peaks from the electrical measurements and a strong photocurrent response due to the formation of a p-n-p junction in gate-dependent scanning photocurrent microscopy. The technique of focused-laser irradiation on a graphene device suggests a new method to control the chargecarrier type and carrier concentration in graphene in a non-intrusive manner as well as elucidate strong light-substrate interactions in the ultimate performance of graphene devices.