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 bear the potential for electronic devices with better performance. However, the mechanism in which charge is transferred or distributed in these heterostructure devices 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 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 charge flow into the GaS from the metal contacts to be 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±8cm2/Vs at room temperature, comparable to that of bare InSe of the same size, and most importantly, an average threshold voltage shift of -8V is observed, indicative of n-type modulation doping of ~0.6x1012/cm2 from the GaS layer.