Electrical Characteristics of Multilayer MoS_2 FET's with MoS_2/Graphene Heterojunction Contacts

摘要

The electrical properties of multilayer MoS_2/ graphene heterojunction transistors are investigated. Temperaturedependent I?V measurements indicate the concentration of unintentional donors in exfoliated MoS_2 to be 3.57 × 10~(11) cm~(?2), while the ionized donor concentration is determined as 3.61 × 10~(10) cm~(?2). The temperature-dependent measurements also reveal two dominant donor levels, one at 0.27 eV below the conduction band and another located at 0.05 eV below the conduction band. The I?V characteristics are asymmetric with drain bias voltage and dependent on the junction used for the source or drain contact. I?V characteristics of the device are consistent with a long channel one-dimensional field-effect transistor model with Schottky contact. Utilizing devices, which have both graphene/MoS_2 and Ti/MoS_2 contacts, the Schottky barrier heights of both interfaces are measured. The charge transport mechanism in both junctions was determined to be either thermionic-field emission or field emission depending on bias voltage and temperature. On the basis of a thermionic field emission model, the barrier height at the graphene/MoS_2 interface was determined to be 0.23 eV, while the barrier height at the Ti/MoS_2 interface was 0.40 eV. The value of Ti/MoS_2 barrier is higher than previously reported values, which did not include the effects of thermionic field emission.