  Transition-metal dichalcogenides (TMDs), such as molybdenum disulfide (MoS2),
are expected to be promising for next generation device applications. The
existence of sulfur vacancies formed in MoS2, however, will potentially make
devices unstable and problematic. Random telegraphic signals (RTSs) have often
been studied in small area Si metal-oxide-semiconductor field-effect
transistors (MOSFETs) to identify the carrier capture and emission processes at
defects. In this paper, we have systemically analyzed RTSs observed in
atomically thin layer MoS2 FETs. Several types of RTSs have been analyzed. One
is the simple on/off type of telegraphic signals, the second is multilevel
telegraphic signals with a superposition of the simple signals, and the third
is multilevel telegraphic signals that are correlated with each other. The last
one is discussed from the viewpoint of the defect-defect interaction in MoS2
FETs with a weak screening in atomically confined two-dimensional electron-gas
systems. Furthermore, the position of defects causing RTSs has also been
investigated by preparing MoS2 FETs with multi-probes. The electron beam was
locally irradiated to intentionally generate defects in the MoS2 channel. It is
clearly demonstrated that the MoS2 channel is one of the RTS origins. RTS
analysis enables us to analyze the defect dynamics of TMD devices.
