On the Electrostatic Control of Gate-Normal-Tunneling Field-Effect Transistors

A gate-normal-tunneling field-effect transistor (gate-normal TFET) with abrupt switching and increased tunneling current is a promising candidate for low-voltage operation in advanced technology nodes. However, it is still challenging to experimentally achieve steep subthreshold swings (SSs) of theoretical predictions. The parasitic nonnormal tunneling initiated prior to the desired normal tunneling due to poor electrostatic control is considered to be one of the explanations for the experimentally inferior SS. This paper investigates the electrostatic control of gate-normal TFETs via numerical simulations in which a semiclassical approximation is used for the tunneling barrier imposed by quantum confinement. The electrostatic potential throughout the device is found to be strongly influenced by quantum effects. As a result, we predicted a higher parasitic tunneling current using our semiclassical simulations (quantum corrected 3-D) compared with classical (nonquantum corrected 3-D) results for gate-normal TFETs with a homojunction. This finding was supported by a qualitative fully quantummechanical (2-D sub-band) study. A heterojunction gate-normal TFET design utilizing an underlying modulation-doping layer is proposed to minimize parasitic tunneling with small variation of quantum confinement and low doping level in the channel.