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 (MoS₂) 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 MoS₂ flake are fabricated on hBN and SiO₂ substrates. This allows for a better and a precise comparison between the charge traps at the semiconductor-dielectric interfaces at MoS₂-SiO₂ and hBN interfaces. The impact of ambient environment and entities on hysteresis is minimized by encapsulating the active MoS₂ layer with a single hBN on both the devices. The device to device variations induced by different MoS₂ layer is also eliminated by employing a single MoS₂ 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 × 10¹¹ cm^-2 on hBN substrate as compared to 1.1 × 10¹² cm^-2 on SiO₂ 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 SiO₂ and hBN substrates further demonstrate the requirement of hBN substrate and encapsulation for improved and stable performance of MoS₂ FETs.