Highly nonlinear biexcitonic photocurrent from ultrafast inter-layer charge transfer

TL;DR

This paper demonstrates a highly nonlinear, ultrafast photocurrent generated by charged biexcitons in a monolayer semiconductor heterostructure, highlighting potential for advanced optoelectronic devices.

Contribution

It reveals the ultrafast inter-layer charge transfer and strong nonlinear photocurrent from charged biexcitons in a graphene-WS2 heterostructure, a novel approach for nonlinear photodetection.

Findings

Large nonlinear photocurrent from charged biexcitons at zero bias.

Ultrafast charge transfer to graphene within 5 ps.

Identification of biexciton origins via photoluminescence spectroscopy.

Abstract

Strong Coulomb interaction in monolayer semiconductors allows them to host optically active large many-body states, such as the five-particle state, charged biexciton. Strong nonlinear light absorption by the charged biexciton under spectral resonance, coupled with its charged nature, makes it intriguing for nonlinear photodetection - an area that is hitherto unexplored. Using the high built-in vertical electric field in an asymmetrically designed few-layer graphene encapsulated 1L-WS$_2$ heterostructure, here we report a large, highly nonlinear photocurrent arising from the strong absorption by two charged biexciton species under zero external bias (self-powered mode). Time-resolved measurement reveals that the generated charged biexcitons transfer to the few-layer graphene in a timescale of sub-5 ps, indicating an ultrafast intrinsic limit of the photoresponse. By using single- and two-color photoluminescence excitation spectroscopy, we show that the two biexcitonic peaks originate from bright-dark and bright-bright exciton-trion combinations. Such innate nonlinearity in the photocurrent due to its biexcitonic origin, coupled with the ultrafast response due to swift inter-layer charge transfer, exemplifies the promise of manipulating many-body effects in monolayers towards viable optoelectronic applications.