ACS Nano 8, 8653–8661 (2014)

Because of their good optoelectronic properties, semiconducting monolayers of transition metal dichalcogenides are being extensively used for the realization of efficient phototransistors. However, the light-conversion performance of these devices is affected by the metals used to contact the semiconductors. Now, Wenjing Zhang and collaborators have studied the potential energy barrier — the Schottky barrier — formed at the junctions between a tungsten diselenide monolayer and the electric contacts, and found that the specific detectivity (a figure of merit used to quantify the response of photodetectors to light illumination) and the response speed of these devices strongly depend on the barrier height. They tuned the energy of the metal–semiconductor contacts by using two different metals and by testing the devices in vacuum and ambient conditions. Their results show that phototransistors having low Schottky barriers reach a detectivity that is higher than that of commercial photodetectors, but have a very slow response. On the other hand, a high barrier can improve the speed and the linearity of the device at the expense of a reduced sensitivity.