Impact of Field-Induced Quantum Confinement on the Subthreshold Swing Behavior of Line TFETs

Abstract

Trap-assisted tunneling (TAT) is a major hurdle in achieving a sub-60-mV/decade subthreshold swing (SS) in tunnel field-effect transistors (TFETs). This paper presents an insight into the TAT process in the presence of field-induced quantum confinement (FIQC) in line TFETs. We show that the SS degradation in line TFETs is mainly caused by TAT through traps located in the bulk of the semiconductor nearby the gate dielectric. For an Si n-type TFET, the energy quantization in the conduction band is found to suppress the TAT through the interface-region traps by several orders of magnitude and delay the TAT through bulk traps nearby the gate dielectric with several hundreds of millivolts. The trap levels closer to the conduction band were found to be the most efficient for TAT in this n-TFET. The FIQC onset voltage shift in TAT through bulk taps is found to be smaller than the band-to-band tunneling (BTBT) shift, enhancing the effective SS degradation in TFETs. We therefore show that it is equally important to include the FIQC effect when calculating TAT as when calculating BTBT generation rates