Semiconductor channel mediated photodoping in h-BN encapsulated monolayer MoSe2 phototransistors

TL;DR

This study demonstrates room-temperature photodoping of h-BN encapsulated monolayer MoSe2 phototransistors using laser excitation, revealing a process driven by optical absorption in the MoSe2 channel that allows controllable tuning of charge density.

Contribution

It extends photodoping techniques from graphene/h-BN heterostructures to MoSe2 monolayer transistors, showing optical absorption as the key mechanism at resonance.

Findings

Photodoping increases carrier density by ~4.45×10^{12} cm^{-2} with 785 nm laser.

Efficiency peaks when excitation matches MoSe2 A exciton absorption.

Photodoping mechanism involves optical absorption in MoSe2, not graphene.

Abstract

In optically excited two-dimensional phototransistors, charge transport is often affected by photodoping effects. Recently, it was shown that such effects are especially strong and persistent for graphene/h-BN heterostructures, and that they can be used to controllably tune the charge neutrality point of graphene. In this work we investigate how this technique can be extended to h BN encapsulated monolayer MoSe_2 phototransistors at room temperature. By exposing the sample to 785 nm laser excitation we can controllably increase the charge carrier density of the MoSe_2 channel by {\Delta}n {\approx} 4.45 {\times} 10^{12} cm^{-2}, equivalent to applying a back gate voltage of 60 V. We also evaluate the efficiency of photodoping at different illumination wavelengths, finding that it is strongly correlated with the light absorption by the MoSe_2 layer, and maximizes for excitation on-resonance with the A exciton absorption. This indicates that the photodoping process involves optical absorption by the MoSe_2 channel, in contrast with the mechanism earlier described for graphene/h-BN heterostroctures.