Single-crystalline monolayer semiconductors with coherent quantum transport by vicinal van der Waals epitaxy

Monolayers of transition metal dichalcogenides, such as molybdenum disulfide, are a potential platform for two-dimensional carrier transport. However, although single-crystalline monolayer channels have been grown at the wafer scale using unidirectional coalescence epitaxy, achieving coherent two-dimensional transport at similar scales remains challenging. This is mainly due to the presence of residual crystalline defects, such as one-dimensional extended and point defects, which emerge when multiple grains coalesce. Here we report an epitaxial growth of single-crystal molybdenum disulfide monolayers at wafer scales in which these defects are minimized by coalescence kinetics control on vicinal sapphire substrates. The resulting channels exhibit coherent transport—manifesting as weak localization and the onset of quantum Hall effects at low temperature—as well as a Hall mobility of 1,200 cm2 V−1 s−1. These coherent channels are used to create arrays of field-effect transistors, which exhibit an average mobility of around 100 cm2 V−1 s−1 and a minimum subthreshold swing of around 65 mV dec−1 at room temperature. By controlling the coalescence of multiple unidirectional grains on vicinal sapphire substrates, wafer-scale channels of single-crystalline molybdenum disulfide can be grown, which exhibit coherent quantum transport across large length scales.