Electrical characteristics of multilayer MoS₂ FETs with MoS ₂/graphene heterojunction contacts

The electrical properties of multilayer MoS₂/graphene heterojunction transistors are investigated. Temperature-dependent I-V measurements indicate the concentration of unintentional donors in exfoliated MoS₂ to be 3.57 × 10¹¹ cm^-2, while the ionized donor concentration is determined as 3.61 × 10¹⁰ 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/MoS₂ and Ti/MoS₂ 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/MoS₂ interface was determined to be 0.23 eV, while the barrier height at the Ti/MoS₂ interface was 0.40 eV. The value of Ti/MoS₂ barrier is higher than previously reported values, which did not include the effects of thermionic field emission.