Electrical Characteristics of Multilayer MoS₂ FET’s with MoS₂/Graphene Heterojunction Contacts

The electrical properties of multilayer MoS₂/graphene heterojunction transistors are investigated. Temperature-dependent <i>I</i>–<i>V</i> 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>I</i>–<i>V</i> characteristics are asymmetric with drain bias voltage and dependent on the junction used for the source or drain contact. <i>I</i>–<i>V</i> 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