The role of charge trapping in MoS ₂ /SiO ₂ and MoS ₂ /hBN field-effect transistors

Abstract

The commonly observed hysteresis in the transfer characteristics of MoS 2 transistors is typically associated with charge traps in the gate insulator. Since in Si technologies such traps can lead to severe reliability issues, we perform a combined study of both the hysteresis as well as the arguably most important reliability issue, the bias-temperature instability. We use single-layer MoS 2 FETs with SiO 2 and hBN insulators and demonstrate that both phenomena are indeed due to traps in the gate insulator with time constants distributed over wide timescales, where the faster ones lead to hysteresis and the slower ones to bias-temperature instabilities. Our data show that the use of hBN as a gate insulator considerably reduces the number of accessible slow traps and thus improves the reliability. However, the reliability of hBN insulators deteriorates with increasing temperature due to the thermally activated nature of charge trapping.

Reversible hysteresis inversion in MoS2 field effect transistors

“…Low sweep rate ensures that nearly all the traps are taking part in the hysteresis phenomenon. 42 We also varied the measurement frequency, f = 1 N ts from 0.002 to 0.27 Hz, where N is the number of voltage step points. 42 However, we did not see any significant change in ΔV TH .…”

Experimental evidence of exciton capture by mid-gap defects in CVD grown monolayer MoSe2

“…22,23 However, very little was known about the role of midgap defects serving as carrier traps in 2D TMDs. Even though defect trapping carriers has been found as the origin of the hysteresis phenomena in electrical I DS -V G measurement of TMD field effect transistors, 25 still, not any spectroscopic signal has been assigned as a direct defect trapping signature in timeresolved transient optical measurements.…”

Highly-stable black phosphorus field-effect transistors with low density of oxide traps

“…At the same time, the use of an effective encapsulation scheme suppresses ambient defects (e.g., adsorbed water molecules), which have been suggested to contribute to the hysteresis in bare MoS 2 /SiO 2 devices. 29 Therefore, the charge trapping dynamics in our BPFETs are dominated by traps in SiO 2 , which can be very well described using our TCAD models. 29 Second, the alignment of the defect bands in SiO 2 with respect to the conduction and valence bands of BP is comparably favorable (see Fig.…”

“…29 Therefore, the charge trapping dynamics in our BPFETs are dominated by traps in SiO 2 , which can be very well described using our TCAD models. 29 Second, the alignment of the defect bands in SiO 2 with respect to the conduction and valence bands of BP is comparably favorable (see Fig. S5 in the SI).…”

“…Then, similarly to ref. 29, we introduce the measurement frequency f = 1/(Nt step ), with N being the number of voltage steps and t step the sampling time. This allows us to express the measurement results in terms of ΔV Hn (f) and ΔV Hp (f) for varied V gmax and V gmin , respectively.…”