Comparison of trapped charges and hysteresis behavior in hBN encapsulated single MoS₂ flake based field effect transistors on SiO₂ and hBN substrates

Abstract

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.

Insulators for 2D nanoelectronics: the gap to bridge

“…5). The most widely observed issues in 2D devices are the hysteresis of the gate transfer characteristics 11,12,45,54,58 and long-term drifts of the threshold voltage [90][91][92] , which are commonly known from Si technologies as BTI, given their strong bias and temperature dependence 85 . Recent analysis of experimental results for MoS 2 58,70,71,93,94 and black phosphorus 23,50 using non-radiative multiphonon (NMP) models 95 (see more details in Box 2) suggests that hysteresis and BTI have the same microscopic origin and result from changes in the charge state of border traps (Fig.…”

“…The most widely studied crystalline insulator for 2D materials is hBN 11,45,54,58 . Devices using hBN typically exhibit a sizable improvement in terms of SS 54 and mobility 11 and also show considerably reduced charge trapping compared to 3D oxides 45,58 . This can be explained by the well-defined surface of hBN and the low density of border traps in this crystalline material.…”

“…Finally, crystalline insulators like layered 2D insulators such as hexagonal boron nitride 45 calcium fluoride 46 (CaF 2 , Fig. 1f) have been used.…”

“…The most widely used are thermally grown SiO 2 13,20,58 as a substrate/back-gate, and conventional high-k oxides such as Al 2 O 3 16 and HfO 2 10,38 for top-gated structures. In addition, the 2D crystalline insulator hBN 11,45,58 , as well as the crystalline CaF 2 46 have been used. The electric parameters of these insulators at a physical thickness of 1 nm EOT are summarized in the band diagram in Fig.…”

P3HT/Phthalocyanine Nanocomposites as Efficient Hole‐Transporting Materials for Perovskite Solar Cells

“…Both methods confirmed that the composite film based on phthalocyanine nanowire and P3HT in the same weight ratio can offer the best hole transfer capability, which is the fundament of high short‐circuit current density ( J SC ) and fill factor (FF) . We also calculated the trap density (N T ) of HTM thin films based on the change in threshold voltage (ΔV T ), obtained by the hysteresis curves of thin films in FET devices and using the formula N T = −ΔV T C ox /q . As shown in Figure , the largest ΔV T between two curves was observed for phthalocyanine nanowire thin film.…”