Reconfigurable carrier type and photodetection of MoTe₂ of various thicknesses by deep ultraviolet light illumination

Tuning of the Fermi level in transition metal dichalcogenides (TMDCs) leads to devices with excellent electrical and optical properties. In this study, we controlled the Fermi level of MoTe₂ by deep ultraviolet (DUV) light illumination in different gaseous environments. Specifically, we investigated the reconfigurable carrier type of an intrinsic p-MoTe₂ flake that gradually transformed into n-MoTe₂ after illumination with DUV light for 30, 60, 90, 120, 160, 250, 500, 900, and 1200 s in a nitrogen (N₂) gas environment. Subsequently, we illuminated this n-MoTe₂ sample with DUV light in oxygen (O₂) gas and reversed its carrier polarity toward p-MoTe₂. However, using this doping scheme to reveal the effect of DUV light on various layers (3-30 nm) of MoTe₂ is challenging. The DUV + N₂ treatment significantly altered the polarity of MoTe₂ of different thicknesses from p-type to n-type under the DUV + N₂ treatment, but the DUV + O₂ treatment did not completely alter the polarity of thicker n-MoTe₂ flakes to p-type. In addition, we investigated the photoresponse of MoTe₂ after DUV light treatment in N₂ and O₂ gas environments. From the time-resolved photoresponsivity at different polarity states of MoTe₂, we have shown that the response time of the DUV + O₂ treated p-MoTe₂ is faster than that of the pristine and doped n-MoTe₂ films. These carrier polarity modulations and photoresponse paves the way for wider applications of MoTe₂ in optoelectronic devices.