NTC devices are promising for low-power logical circuits, memories, oscillating and high-speed switching applications. In a typical n-type NTC transistor, the output current decreases with increasing gate voltage. It increases with increasing gate voltage in a p-type NTC device.
Previous NTC devices were found to work by either quantum-mechanical tunnelling or thanks to charge mobilities degrading at high electrical fields. A team of researchers led by Xiangfeng Duan of the University of California at Los Angeles (UCLA) has now discovered a third possible mechanism by investigating the charge transport in multilayer 2D semiconductors (2DSCs) made from MoS2 containing optimized van der Waals contacts.
MoS2 belongs to the family of single-layer transition-metal dichalcogenides (TMDs). These are quasi-two-dimensional materials with the chemical formula MX2, consisting of an atomic plane of a transition metal M (Ti, Nb, Mo, Re) sandwiched between the atomic planes of a chalcogen X (S, Se or Te). These materials go from being indirect band-gap semiconductors in the bulk to direct band-gap semiconductors when scaled down to monolayer thickness. These monolayers efficiently absorb and emit light and so might find use in a variety of electronic and optoelectronic device applications.