Carrier-Type Modulation and Mobility Improvement of Thin MoTe2

Abstract

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 O-2 environment (p-type modulation) and benzyl viologen (BV) doping (n-type modulation). Al2O3 capping is then introduced to improve the carrier mobilities and device stability. MoTe2 is found to be ultrasensitive to O-2 at elevated temperatures (250 degrees 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 O-2, 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 10(6) are achieved under optimized doping conditions. By introducing Al2O3 capping, carrier field effect mobilities (41 for holes and 80 cm(2) 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. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim