Intrinsic Photoconductivity Imaging of Monolayer-Bilayer WSe₂ Flakes

The spatial variation of photo response in few-layer transition metal dichalcogenides (TMDCs) is of critical importance for their applications in optoelectronic devices. In conventional microscopy experiments, the local distribution of photocurrent across source and drain electrodes is measured, which may be complicated by the diffusion of photo-induced carriers, the Schottky contact, and other extrinsic effects. Using a microwave impedance microscope (MIM) with light stimulation, we demonstrate the intrinsic photoconductivity mapping of CVD-grown WSe₂ flakes without the need of contact electrodes. The measured photoconductivity as a function of the above-gap laser intensity in the bilayer WSe₂ region is around one order of magnitude higher than that in the monolayer area, indicative of a significant enhancement of the carrier lifetime due to interlayer coupling. The noninvasive MIM imaging is expected to provide important insights on the remarkable electrical and optical properties of TMDCs.