The Effect of Dopant and Thickness on the Electrical Behavior of silicon nanowires

Abstract

Recently accumulation mode silicon nanowire transistors are in interest due to their near ideal subthreshold slope, large on state current and excellent DIBL. These transistors can be realized even without any dedicated source/drain junctions eliminating the need for costly ultrafast annealing techniques for abrupt junction fabrication and permits one to fabricate device with shorter channel lengths. Silicon nanowire transistors also have significant influence on disease diagnosis as silicon nanowire transistors have been shown to function as high sensitivity transducers due to their smaller size and large surface to volume ratio. However, the accumulation mode transistor behavior of silicon nanowires may depend on doping which in turn may depend on nanowire thickness and hence, effective surface to volume ratio for onset of transistor action may vary with doping. In this work accumulation mode transistor behavior of p-type silicon nanowires are investigated at different doping concentrations and nanowire thicknesses to find out the relationship between NW thicknesses and doping for transistor action. The investigation is done for nanowire thicknesses ranging from 5nm to 100 nm with doping density diverging from 1014cm-3 to 1020 cm-3. It is found that thick nanowire‘s transistor action is limited only at low doping concentrations whereas thin nanowires are able to exhibit transistor action at high doping densities even at 1019 cm-3 which is close to source/drain doping of conventional MOSFET. This phenomenon is explained by the gradually decreasing gate modulated volume in the NW with increasing doping concentrations thereby limiting the thickness of nanowires at high doping densities to ensure the whole constricted volume to be affected by gate voltage for onset of transistor action. This research would give insight into the required doping for any particular NW thickness for bio-sensing application and junction less NW transistor fabrication.