Hybrid quantum dot-graphene layers with improved optical properties in the terahertz spectrum region

Abstract

Recently, it has been shown that the graphene plasmonic (GP) effect can enhance the optical properties of quantum dots (QDs) through the Purcell's effect. This can happen when the electromagnetic field is concentrated tightly in a region where the ground state (S-state) and the first excited state (P-state) of electron are present, and the S-to-P transition frequency falls onto the frequency of plasmonic resonance of graphene layers. Here, we use a hybrid composition of graphene layers, consisting of a disk and four L-shaped layers, and a QD aimed to enhance the linear and third-order optical susceptibilities of QD in the terahertz (THz)/far infrared (FIR) spectrum region. Unlike the previous works, where much more graphene layers were used, in this work, we use fewer layers beneath the wetting layer and with a noticeably simpler scheme, we achieve comparable results in transition dipole moments (TDMs) and optical properties. By changing the Fermi's energy of graphene, we could reach 90-fold enhancement for TDM and 8 × 10 3 - and 6 × 10 7 -fold enhancements, respectively, for linear and third-order susceptibilities. Our scheme can noticeably reduce the difficulties in fabricating hybrid graphene-QD systems. • Graphene flakes in nanodisk and L-shaped geometry have been placed in conic-shaped InAs/GaAS quantum dots (QDs). • The emission of QDs has been tuned with graphene plasmonic (GP). • With use of GP effect, S-to-P transition dipole moment (TDM) of QD has been enhanced 120 times. • Linear susceptibility of QD has been multiplied by a factor of 8 × 10 3 . • Third-order susceptibility of QD has been multiplied by a factor of 6 × 10 7 . • GP has been used as a passive method to enhance significantly the optical properties of QDs.