2D materials in field-effect transistors: effects of pressure, temperature and e-beam irradiation

2D materials have been the subject of intense research in the past decade for their electrical behavior tunable by the number of layers, the strong interaction with light, the absence of dangling bonds enabling the formation of van der Waals heterostructures, the mechanical strength and the chemical stability. In this study we fabricate back-gate field-effect transistors using nanosheets of layered materials such as MoS2, PdSe2 or GeAs, deposited on SiO2/Si substrate and contacted with different metals. We report the effect of gas pressure and e-beam irradiation on the electrical transport of MoS2 and PdSe2 nanosheets. We show that gas adsorption enhances the hysteresis in the transfer characteristics of the transistors and that gas pressure controls the polarity of the devices, making n-type conduction dominant in a high vacuum. We exploit the n-type conduction to extract a field emission current in high vacuum. We also investigate the temperature dependence of the electrical conductivity of GeAs nanosheets and report an anomalous peak in the 2D carrier density at temperature around 75 K, that we interpret as the manifestation of a 2D conduction phenomenon.