Lateral and vertical two-dimensional heterostructure devices, in particular graphene-MoS2, have attracted profound interest as they offer additional functionalities over normal two-dimensional devices. Here, we have carried out electrical and optical characterization of graphene-MoS2 heterostructure. The few-layer MoS2 devices with metal electrode at one end and monolayer graphene electrode at the other end show nonlinearity in drain current with drain voltage sweep due to asymmetrical Schottky barrier height at the contacts and can be modulated with an external gate field. The doping effect of MoS2 on graphene was observed as double Dirac points in the transfer characteristics of the graphene field-effect transistor (FET) with a few-layer MoS2 overlapping the middle part of the channel, whereas the underlapping of graphene have negligible effect on MoS2 FET characteristics, which showed typical n-type behavior. The heterostructure also exhibits a strongest optical response for 520 nm wavelength, which decreases with higher wavelengths. Another distinct feature observed in the heterostructure is the peak in the photocurrent around zero gate voltage. This peak is distinguished from conventional MoS2 FETs, which show a continuous increase in photocurrent with back-gate voltage. These results offer significant insight and further enhance the understanding of the graphene-MoS2 heterostructure.

An ambipolar dual-channel field-effect transistor (FET) with a WSe /MoS heterostructure formed by separately controlled individual channel layers is demonstrated. The FET shows a switchable ambipolar behavior with independent carrier transport of electrons and holes in the individual layers of MoS and WSe , respectively. Moreover, the photoresponse is studied at the heterointerface of the WSe /MoS dual-channel FET.

Molybdenum disulfide (MoS) based field effect transistors (FETs) are of considerable interest in electronic and opto-electronic applications but often have large hysteresis and threshold voltage instabilities. In this study, by using advanced transfer techniques, hexagonal boron nitride (hBN) encapsulated FETs based on a single, homogeneous and atomic-thin MoS flake are fabricated on hBN and SiO substrates. This allows for a better and a precise comparison between the charge traps at the semiconductor-dielectric interfaces at MoS-SiO and hBN interfaces. The impact of ambient environment and entities on hysteresis is minimized by encapsulating the active MoS layer with a single hBN on both the devices. The device to device variations induced by different MoS layer is also eliminated by employing a single MoS layer for fabricating both devices. After eliminating these additional factors which induce variation in the device characteristics, it is found from the measurements that the trapped charge density is reduced to 1.9 × 10 cm on hBN substrate as compared to 1.1 × 10 cm on SiO substrate. Further, reduced hysteresis and stable threshold voltage are observed on hBN substrate and their dependence on gate sweep rate, sweep range, and gate stress is also studied. This precise comparison between encapsulated devices on SiO and hBN substrates further demonstrate the requirement of hBN substrate and encapsulation for improved and stable performance of MoS FETs.

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