Analysis of strain effects on schottky - barrier single - and double - walled carbon nanotube transistors

Abstract

A full band quantum mechanical simulation model using pz orbital of carbon atom is developed to study the transport physics of uniaxial and torsional strained double- walled (DW) carbon nanotube (CNT) ¯eld-e®ect transistors (FETs) and to analyze their performance. The characteristics and performance of our proposed DW CNT- FET are compared with existing SW CNTFET. It is shown that both the uniaxial and torsional strain can change the band gap of DW CNT and this band gap is the minimum of the two band gaps of the tubes from which DWCNT is constituted. The strain has large impact on the I-V characteristics of both SW and DW CNT devices. Tensile and torsional strains improve greatly the o®-state current and on/o® current ratio of both devices. Compressive strain improves on-state current, but this im- provement is comparatively small. The e®ect of strain on o®-state current, on-state current and on/o® current ratio is higher in SW CNTFET. The inverse subthreshold slope of DW CNTFET is better than SW CNTFET. But the variation of inverse subthreshold slope with strain is smaller in DW CNTFET. The e®ect of strain on C-V characteristics is observed. Unlike SW CNTFET the on-state transconductance of DWCNTFET increases with tensile and torsional strains and decreases with com- pressive strain. The on-state cut-o® frequency of DW CNTFET also shows opposite behavior to SW CNTFET with strain following on-state transconductance. Intrin- sic switching delay improves greatly with compressive strain only for both devices. Again the SW CNTFET exhibits better change with strain than DW CNTFET. Concrete Physical description is provided to explain all above changes with strain. To complete the whole analysis of DW CNTFET the dimensions of the device are varied and their e®ects on the performance are observed.