Nature of Electronic States in Atomically Thin MoS₂ Field-Effect Transistors

Abstract

We present low-temperature electrical transport experiments in five field-effect transistor devices consisting of monolayer, bilayer, and trilayer MoS(2) films, mechanically exfoliated onto Si/SiO(2) substrate. Our experiments reveal that the electronic states in all films are localized well up to room temperature over the experimentally accessible range of gate voltage. This manifests in two-dimensional (2D) variable range hopping (VRH) at high temperatures, while below ∼30 K, the conductivity displays oscillatory structures in gate voltage arising from resonant tunneling at the localized sites. From the correlation energy (T(0)) of VRH and gate voltage dependence of conductivity, we suggest that Coulomb potential from trapped charges in the substrate is the dominant source of disorder in MoS(2) field-effect devices, which leads to carrier localization, as well.

Universal ac conduction in large area atomic layers of CVD-grown MoS2

“…Thus, we can conclude that for temperatures ranging from 60 to 333 K, and in CVD-grown layers of MoS 2 , the 2D-VRH is the predominant conduction mechanism. Here, it is important to emphasize that such behavior was also observed in highly crystalline, few-layered samples of mechanically exfoliated MoS 2 with values of T 0 ∼ 10 4 − 10 6 K [19]. To gain further insight into the nature of the conduction mechanism, we also measured the ac conductivity of MoS 2 samples.…”

“…However, the materials produced using these techniques are, in general, susceptible to structural disorder [16,17]. Such disorder is known to affect the properties of the material; for example, in semiconductors, atomic defects and bonding disorder influence their band structure, which in turn influences their charge transport [18,19] properties. Therefore, understanding the correlation between the structure and physical properties of these materials is of fundamental interest.…”

Two-dimensional inorganic analogues of graphene: transition metal dichalcogenides

“…Temperaturedependent electrical transport measurements revealed variable range hopping transport at lower temperatures which can be explained by the Coulomb potential of randomly distributed charges at the MoS 2 -SiO 2 interface [102]. Integrated small-signal analogue amplifiers were fabricated by connecting in series two top-gated single-layer MoS 2 transistors [103].…”

Electronic transport and device prospects of monolayer molybdenum disulphide grown by chemical vapour deposition

“…However, the mobility of CVD MoS 2 is typically much lower than its exfoliated counterpart, with reported values in the range of 5 to 22 cm 2 V À 1 s À 1 (refs 34-36). The physical origin of the differences between CVD and exfoliated MoS 2 is not clear at present; however, structural defects 37 such as vacancies, dislocations, grain boundaries as well as charged interfacial states due to the dielectrics in contact 14 can be responsible for the degradation in mobility. Although this problem has presented a major hurdle to the realization of wafer-scale MoS 2 electronics and photonics, systematic studies of it are very few 35 .…”