Defect-tuned conduction in ultrathin MoTe2 field-effect transistors

Abstract

In atomically thin electronics, interfaces and interfacial defects play a critical role in determining device performance. Herein, interfaces with metal contacts, gate dielectrics, and ambient environments are systematically investigated in p-type field-effect transistors with an ultrathin MoTe₂ channel, through temperature- and pressure-dependent measurements, supported by density functional theory calculations. The device performance, likely influenced by Te and Mo vacancies, is enhanced under reduced pressure. Low and nearly symmetric Schottky barrier heights around 37 ± 3 meV are extracted at the metal/semiconductor interfaces through temperature-dependent measurements. The temperature dependence of the mobility suggests that ionized-impurity scattering is possibly associated with Te and Mo vacancies, as a relevant transport mechanism below 300 K, while acoustic-phonon scattering prevails at higher temperatures. Both the subthreshold swing and threshold voltage increase exponentially with temperature, consistent with thermally activated transport mechanisms from band-tail states. A stepwise increase in pressure, starting from vacuum and gradually introducing ambient air, leads to reduced mobility and conductance, which is consistent with progressive molecular physisorption that introduces additional scattering. Near atmospheric pressure, adsorbates are likely to contribute significantly to p-type doping. Taken together, these results elucidate how vacancies, interface traps, and surface adsorbates may govern charge transport in MoTe₂ and provide quantitative guidelines for defect and interface engineering that may also be relevant to other two-dimensional semiconductor devices.