Graphene plasmonic coupling with intersubband radiation of truncated pyramidal-shaped InAs/GaAs quantum dots

Abstract

It is well known that the intersubband radiation of InAs/GaAs quantum dots (QDs) falls in the terahertz/far-infrared spectral region. If these so-called atom-like systems are placed in the vicinity of graphene, their radiation can be coupled with plasmonic modes of graphene. As the graphene plasmons tightly concentrate the electromagnetic waves in the small zones, beyond the diffraction limit, the optical properties of QDs can then be enhanced by the so-called Purcell effect if frequency tuning and mode overlapping are well performed. Owing to this idea, in this work, we report on the enhancement of linear and third-order optical susceptibilities of truncated pyramidal-shaped InAs/GaAs QDs with use of graphene plasmonics. Graphene flakes in various configurations were located inside the QDs, and their transition dipole moments (TDMs) were calculated. Our results show 120-fold enhancement in TDM with optimization on the flakes’ and QDs’ geometries. Consequently, the linear and nonlinear optical susceptibilities of QDs are enhanced noticeably. Precisely, the linear and third-order susceptibilities of QDs with base length of 25 nm and height of 3 nm were enhanced enormously up to ${1.18} \\times {{10}^5}$ and ${1.4} \\times {{10}^{10}}$ times, respectively. This passive method is promising for enhancing the performance of QD-based optoelectronic devices such as lasers, LEDs, sensors, and so on.