Carrier-Type Modulation and Mobility Improvement of Thin MoTe₂

A systematic modulation of the carrier type in molybdenum ditelluride (MoTe₂ ) field-effect transistors (FETs) is described, through rapid thermal annealing (RTA) under a controlled O₂ environment (p-type modulation) and benzyl viologen (BV) doping (n-type modulation). Al₂ O₃ capping is then introduced to improve the carrier mobilities and device stability. MoTe₂ is found to be ultrasensitive to O₂ at elevated temperatures (250 °C). Charge carriers of MoTe₂ flakes annealed via RTA at various vacuum levels are tuned between predominantly pristine n-type ambipolar, symmetric ambipolar, unipolar p-type, and degenerate-like p-type. Changes in the MoTe₂ -transistor performance are confirmed to originate from the physical and chemical absorption and dissociation of O₂ , especially at tellurium vacancy sites. The electron branch is modulated by varying the BV dopant concentrations and annealing conditions. Unipolar n-type MoTe₂ FETs with a high on-off ratio exceeding 10⁶ are achieved under optimized doping conditions. By introducing Al₂ O₃ capping, carrier field effect mobilities (41 for holes and 80 cm² V^-1 s^-1 for electrons) and device stability are improved due to the reduced trap densities and isolation from ambient air. Lateral MoTe₂ p-n diodes with an ideality factor of 1.2 are fabricated using the p- and n-type doping technique to test the superb potential of the doping method in functional electronic device applications.