Real-time effect of electron beam on MoS(2)field-effect transistors

Abstract

Irradiation of MoS(2)field-effect transistors (FETs) fabricated on Si/SiO(2)substrates with electron beams (e-beams) below 30 keV creates electron-hole pairs (EHP) in the SiO2, which increase the interface trap density (N-it) and change the current path in the channel, resulting in performance changes.In situmeasurements of the electrical characteristics of the FET performed using a nano-probe system mounted inside a scanning electron microscope show that e-beam irradiation enables both multilayer and monolayer MoS(2)channels act as conductors. The e-beams mostly penetrate the channel owing to their large kinetic energy, while the EHPs formed in the SiO(2)layer can contribute to the conductance by flowing into the MoS(2)channel or inducing the gate bias effect. The analysis of the device parameters in the initial state and the vent-evacuation state after e-beam irradiation can clarify the effect of the interplay between the e-beam-induced EHPs and ambient adsorbates on the carrier behavior, which depends on the thickness of the MoS(2)layer. DC and low frequency noise analysis reveals that the e-beam-induced EHPs increaseN(it)from 10(9)-10(10)to 10(11)cm(-2)eV(-1)in both monolayer and multilayer devices, while the interfacial Coulomb scattering parameter alpha(SC)increases by three times in the monolayer and decreases to one-tenth of its original value in the multilayer. In other words, an MoS(2)layer with a thickness of similar to 30 nm is less sensitive to adsorbates by surface screening. Thus, the carrier mobility in the monolayer device decreases from 45.7 to 40 cm(2)V(-1)s(-1), while in the 30 nm-thick multilayer device, it increases from 4.9 to 5.6 cm(2)V(-1)s(-1). This is further evidenced by simulations of the distribution of interface traps and channel carriers in the MoS2FET before and after e-beam irradiation, demonstrating that Coulomb scattering decreases as the effective channel moves away from the interface.