Monolayer

We present a method for the nanoscale mapping of photoconductivity and charge trap density in the grain structures of a monolayer molybdenum disulfide (MoS₂). In this method, the lateral current and noise maps were measured by scanning the MoS₂ surface with a nanoscale conducting contact probe. The measured data were analyzed to obtain the sheet resistance and charge trap density maps in the MoS₂ grain structures. Interestingly, the sheet resistance was found inversely proportional to the charge trap density in the grains. It was explained by the sulfur vacancies working as both charge hopping sites and traps in the MoS₂ monolayer. When illuminated with a light, the regions with a relatively high trap density showed a high photoconductivity. These results indicate that high photoconductivity was enhanced by charge traps. This method can be a powerful tool for the basic research about noises and the device applications based on two-dimensional materials.