Abstract
In optically excited 2D 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 MoSe2 phototransistors at room temperature. By exposing the sample to 785 nm laser excitation we can controllably increase the charge carrier density of the MoSe2 channel by Δn ≈ 4.45 × 1012 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 MoSe2 layer, and maximizes for excitation on-resonance with the A exciton absorption. This indicates that the photodoping process involves optical absorption by the MoSe2 channel, in contrast with the mechanism earlier described for graphene/h-BN heterostroctures.
Highlights
Two-dimensional (2D) transition metal dichalcogenides (TMDs) are very attractive materials for the design of optoelectronic devices at the nanoscale [1,2,3,4,5] due to their optical bandgap spanning the visible spectrum, large photoresponse, and high carrier mobility
In this work we investigate how this technique can be extended to hexagonal boron nitride (h-BN) encapsulated monolayer MoSe2 phototransistors at room temperature
By testing the dependence of photodoping on the excitation energy, we find that this effect only occurs for excitation wavelengths above the absorption edge of 1L-MoSe2, indicating that the photodoping effect is mediated by optical excitation of this material, in contrast with earlier theoretical descriptions for graphene/h-BN structures [20], where photodoping was attributed to the optical excitation of h-BN impurity states [22,23,24,25,26,27,28]
Summary
Keywords: two-dimensional materials, photodoping, phototransistors, molybdenum diselenide (MoSe2) Supplementary material for this article is available online Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence.
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