Modulation Doping and Reduced Hysteresis in Monochalcogenide InSe/GaS Heterostructure 2D Field-Effect Transistors

Heterostructures made from 2D materials have led to the discovery of many new electronic phases and have the potential for electronic devices with better performance. However, the mechanism by which charge is transferred or distributed in these novel heterostructure devices made of atomically thin semiconductors is yet to be fully understood. By creating and electronically characterizing InSe/GaS heterostructure field-effect transistors with different metal contact configurations, we observed a decrease in the maximum on-current and an increase in the hysteresis when both the InSe and GaS layers are in contact with the metal contacts. This, combined with the time-dependent conductance decay measurements, suggests that charge flow into the GaS from the metal contacts is the source of the hysteresis, which can be mitigated by encapsulating the GaS with InSe. Our resultant nearly hysteresis-free devices exhibit an average field-effect mobility of 34 ± 8 cm²V^-1s^-1 at room temperature, comparable to that of bare InSe of the same size, with an average n-type modulation doping of ∼ 1 × 10¹² cm^-2 from the GaS layer.