Molybdenum disulfide (MoS ₂ ) 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 ₂ flake are fabricated on hBN and SiO ₂ substrates. This allows for a better and a precise comparison between the charge traps at the semiconductor-dielectric interfaces at MoS ₂ −SiO ₂ and hBN interfaces. The impact of ambient environment and entities on hysteresis is minimized by encapsulating the active MoS ₂ layer with a single hBN on both the devices. The device to device variations induced by different MoS ₂ layer is also eliminated by employing a single MoS ₂ 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 ¹¹ cm ⁻² on hBN substrate as compared to 1.1 × 10 ¹² cm ⁻² on SiO ₂ 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 ₂ and hBN substrates further demonstrate the requirement of hBN substrate and encapsulation for improved and stable performance of MoS ₂ FETs.

InAs quantum dots inserted at the middle of a GaAs quantum well structure have been investigated by transmission electron microscopy and scanning transmission electron microscopy. We find that the growth condition of the overlayer on the InAs dots can lead to drastic changes in the structure of the dots. We attribute the changes to a combination of factors such as preferential growth of the overlayer above the wetting layers because of the strained surfaces and to the thermal instability of the InAs dots at elevated temperature. The result suggests that controlled sublimation, through suitable manipulation of the overlayer growth conditions, can be an effective tool to improve the structure of the self-organized quantum dots and can help tailor their physical properties to any specific requirements of the device applications.