Local inhomogeneity in gate hysteresis of carbon nanotube field-effect transistors investigated by scanning gate microscopy

Local nature of gate hysteresis in a carbon nanotube field-effect transistor (CNFET) was studied using scanning gate microscopy (SGM). A sequential set of SGM images of the CNFET fabricated on a SiO2/Si substrate was obtained at a low temperature under an ultra-high vacuum. Comparisons of the SGM images obtained at decreasing and increasing gate voltage steps revealed that the order of appearance of SGM defects could not be accounted for by a uniform distribution of hysteretic gate screening along the carbon nanotube (CNT) channel. It was concluded that the gate hysteresis in the CNFET had substantial local variations along the CNT. The local inhomogeneity in gate hysteresis was attributed to inhomogeneous distribution of screening charge traps or sources on the SiO2 surface.