Highly Sensitive, Fast Graphene Photodetector with Responsivity $>10^6$ A/W Using Floating Quantum Well Gate

TL;DR

This paper presents a graphene-based heterojunction photodetector with ultra-high responsivity over 10^6 A/W, fast response, and low noise, achieved through a floating quantum well gate that enhances photogating effects.

Contribution

The work introduces a novel graphene/WS2/MoS2 heterojunction with a floating quantum well gate, significantly improving responsivity and speed over previous graphene photodetectors.

Findings

Responsivity of 4.4×10^6 A/W at 30 fW incident power

Noise equivalent power below 4 fW/√Hz

Response time of approximately milliseconds

Abstract

Graphene, owing to its zero bandgap electronic structure, is promising as an absorption material for ultra-wideband photodetection applications. However, graphene-absorption based detectors inherently suffer from poor responsivity due to weak absorption and fast photocarrier recombination, limiting their viability for low intensity light detection. Here we use a graphene/WS$_2$/MoS$_2$ vertical heterojunction to demonstrate a highly sensitive photodetector, where the graphene layer serves dual purpose, namely as the light absorption layer, and also as the carrier conduction channel, thus maintaining the broadband nature of the photodetector. A fraction of the photoelectrons in graphene encounter ultra-fast inter-layer transfer to a floating monolayer MoS$_2$ quantum well providing strong quantum confined photogating effect. The photodetector shows a responsivity of $4.4\times 10^6$ A/W at 30 fW incident power, outperforming photodetectors reported till date where graphene is used as light absorption material by several orders. In addition, the proposed photodetector exhibits an extremely low noise equivalent power ($N\!E\!P$) of $<4$ fW/$\sqrt{Hz}$ and a fast response ($\sim$ milliseconds) with zero reminiscent photocurrent. The findings are attractive towards the demonstration of graphene-based highly sensitive, fast, broadband photodetection technology.