Electrostatic modulation of excitonic fluid in GaN/AlGaN quantum wells by deposition of few-layer graphene and nickel/gold films

Excitons hosted by GaN/(Al,Ga)N quantum wells (QWs) are spatially indirect due to the giant built-in electric field that separates electrons and holes along the growth direction. This electric field, and thus exciton energy, can be reduced by depositing metallic layers on the sample surface. Using spatially resolved microphotoluminescence spectroscopy we compare the effects of two different materials, nickel/gold (NiAu) and few-layer graphene (FLG), on the potential landscape experienced by the excitons. We are able to (i) determine the potential barriers imposed on QW excitons by deposition of FLG and NiAu to be 14 and 82 meV, respectively, and (ii) to evince their impact on the exciton transport at appropriate densities. Optical losses and inhomogeneous broadening induced by deposition of NiAu and FLG layers are similar, and their joined implementation constitute a promising tool for electrostatic modulation of exciton densities even in the absence of any applied electric bias.