Transport properties of InAs nanowire field effect transistors: The effects of surface states

It is shown that interface trap states have pronounced effects on carrier transport and parameter extraction from top-gated InAs nanowire field effect transistors NWFETs . Due to slow surface state charging and discharging, the NWFET characteristics are time dependent with time constants as long as 45 s. This is also manifested in a time-dependent extrinsic transconductance that severely affects carrier mobility and carrier density determination from conventional three-terminal current-voltage characteristics. Slow gate voltage sweep rates result in charge balance between carrier capture and emission from interface states and lead to reduced hysteresis in the transfer curves. The gate transconductance is thus increased and intrinsic NW transport parameters can be isolated. In the InAs NWFETs, a carrier mobility value of 16 000 cm2/V s was obtained from the transfer curves at slow sweep rates, which is significantly higher than 1000 cm2/V s obtained at fast sweep rates. A circuit model that takes into account the reduction in the extrinsic transconductance is used to estimate an interface state capacitance to be 2 F/cm−2, a significant value that can lead to underestimation of carrier mobility. © 2007 American Vacuum Society. DOI: 10.1116/1.2748410