Band Gap Estimation of Multilayer 2D Semiconductor Channels Using Thin Graphite Contact

Band gap of monolayer and few layers in two dimensional (2D) semiconductors has usually been measured by optical probing such as photoluminescence (PL). However, if their exfoliated thickness is as large as a few nm (multilayer over ~5L), PL measurements become less effective and inaccurate because the optical transition of 2D semiconductor is changed from direct to indirect mode. Here, we introduce another way to estimate the bandgap of multilayer 2D van der Waals semiconductors; that is utilizing field effect transistor (FET) as a platform. We used graphene (thin graphite or multilayer graphene) contact for multilayer van der Waals channels in FET, because graphene contact would secure ambipolar behavior and enable Schottky contact barrier tuning of FETs with the assistance of top passivation. As a result, the bandgaps of multilayer transition metal dichalcogenides and black phosphorus in unknown thickness were successfully estimated through measuring the temperature-dependent transfer curve characteristics of prepared 2D FETs with graphene contact.