Analysis of the subthreshold characteristics of vertical tunneling field effect transistors
垂直隧穿场效应晶体管的亚阈值特性分析

Subthreshold characteristics of vertical tunneling field effect transistors (VTFETs) with an n+-pocket in the p+-source are studied by simulating the transfer characteristics with a commercial device simulator. Three types of subthreshold characteristics are demonstrated for the device with different pocket thicknesses and doping concentrations. Band diagram analysis shows that such a VTFET can be treated as a gate-controlled tunnel diode connected in series with a conventional n-channel metal-oxide-semiconductor FET. This VTFET can work either as a TFET or an n-MOSFET in the subthreshold region, depending on the turn-on sequence of these two components. To our knowledge, this is the first time such a device model has been used to explain the subthreshold characteristics of this kind of VTFET and the simulation results demonstrate that such a device model is convictive and valid. Our results indicate that the design of the n+ pocket is crucial for such a VTFET in order to achieve ultra-steep turn-on characteristics.