Study of light matter interactions in ultra low noise graphene based van der Waals hybrid

Abstract

The vast array of optical and electrical capabilities of graphene (Gr) and analogous two dimensional (2D) van der Waals (vdW) materials have piqued scientists interest for long. Stacking these materials to form hybrid heterostructures provide a versatile platform to explore a variety of fundamental physical phenomena such as light-matter interactions, lattice-strain engineering, quantum phenomenon, electron-phonon interactions and so on. The recent progress in Gr-based photonic devices, especially with transition metal dichalcogenides (TMDCs), shows their true potential in optoelectronics with remarkably strong light absorbing capabilities and high photo-responsivity. However, despite extensive investigation of device applications, like solar cells, photodetectors, ultra fast lasers, sensors, quantum technologies etc, understanding of underlying physical mechanisms is still in its incipient stages. This thesis encompasses a study of optoelectronic responses in optimized ultra-low noise Gr-TMDC hybrid field effect transistors (FETs). Here, we first explore the interlayer charge transfer mechanisms in Gr-TMDC heterostructure by engineering the spectral dependence of photoresponse. We show that the Gr-TMDC FETs exhibit a large photoresponse not only for visible photons, which have energy (E_{Ph}) greater than the bandgap (E_g) of the TMDC (i.e., E_{Ph} gt E_g), but also for NIR photons, which have E_{Ph}lt E_g, where both follow the photogating effect. This sub-band gap photoresponse is attributed to mid-gap states present in the TMDC layer. Moreover, we study the bidirectional charge transfer in the optically excited state using both excitation sources together (i.e., visible and NIR photons). We demonstrate that the excess electrons in graphene by absorbing the NIR photons, back transfer from graphene to TMDC. Using visible and NIR light pulses in various sequences, we show that the bidirectional interlayer charge transfer can be controlled...