Explicit Gain Equations for Hybrid Graphene‐Quantum‐Dot Photodetectors

Abstract

Graphene is an attractive material for broadband photodetection but suffers from weak light absorption. Coating graphene with quantum dots can significantly enhance light absorption and create extraordinarily high photogain. This high gain is often explained by the classical gain theory which is unfortunately an implicit function and may even be questionable. In this work, explicit gain equations for hybrid graphene‐quantum‐dot photodetectors are derived. Because of the work function mismatch, lead sulfide quantum dots coated on graphene will form a surface depletion region near the interface of quantum dots and graphene. Light illumination narrows down the surface depletion region, creating a photovoltage that gates the graphene. As a result, high photogain in graphene is observed. The explicit gain equations are derived from the theoretical gate transfer characteristics of graphene and the correlation of the photovoltage with the light illumination intensity. The derived explicit gain equations fit well with the experimental data, from which physical parameters are extracted.The classical photoconductive gain theory is not only questionable, but also an implicit function of illumination light intensity and device parameters. In this work, explicit photoconductive gain equations are derived for graphene devices coated with lead sulfide quantum dots. The gain equations fit well with the experimental data and therefore allow for designing and predicting photoresponses of the graphene‐quantum‐dot photodetectors.