Source Engineering for Tunnel Field-Effect Transistor: Elevated Source with Vertical Silicon–Germanium/Germanium Heterostructure

Abstract

In this work, we demonstrate by simulation and experiment that the performance of a p+ Si0.5Ge0.5 source tunnel field-effect transistor (TFET) can be improved by inserting an undoped Ge layer between source and channel. The Ge layer suppresses diffusion of boron into the Si channel and it also forms a Si0.5Ge0.5/Ge/Si hole quantum well, leading to an abrupt boron profile and a high hole concentration at the source edge. At the Ge/Si heterojunction, the presence of compressive strain in the Ge layer increases the valence band offset, while the tensile strain in the Si channel increases the conduction band offset, which effectively reduces the tunnel barrier and enhances the tunnel probability. Compared with a control device without the Ge layer, TFETs with a Si0.5Ge0.5/Ge source show a higher on-state current I ON and improved threshold voltage V TH and subthreshold characteristics.

Design Optimization of Extremely Short-Channel Graded Si/Sige Heterojunction Tunnel Field-Effect Transistors for Low Power Applications

“…The operating characteristics of any SiGe-based TFETs rely highly on device parameters such as source/drain doping profiles [20,28] and Ge concentration [2,4,10] which modifies the bandgap of Si-Ge alloy. Each parameter differently affects, in both manner and degree, the device performance.…”

“…The design optimization of the source and the drain are then considered subsequently. In single material-based TFET, higher source doping and larger abruptness greatly improve the on-current and SS [20,28]. Thereby, the effect of source doping profile is first investigated and optimized appropriately.…”

“…It has been shown in long-channel TFETs that the source with as heavy doping and high abruptness as possible is expected to improve the on-current and SS [20,28]. Because of a novel graded SiGe layer formed in the channel and the source and drain junctions are very close to each other in this proposed TFET, the effect of source doping profile may present differently, and therefore the role of source must be investigated in detail.…”

Radio-frequency modeling of square-shaped extended source tunneling field-effect transistors

“…Due to low on-current of silicon-based TFETs, different techniques have been suggested to improve the on-current. On-current of TFETs can be enhanced by using band-gap engineering [10][11][12][13][14][15][16][17], small band-gap materials [18,19], high-j dielectric materials [20], pocket doping [21][22][23], vertical direction tunneling [24] and extended source [25]. Second challenge is not fully the understanding device physics that causes questionable the applicability of WKB approximation for phonon or impurity scattering and indirect bandgap semiconductors, such as Si and Ge [26].…”

Simulation of tunneling field-effect transistors with extended source structures

“…TFETs with sub-60 mV/decade S have been demonstrated experimentally, but achieving I on comparable with state-of-the-art CMOS is challenging. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] There have been many TFET research efforts directed at improving the on-state current. I on in TFETs can be significantly enhanced by tuning the band alignment between the source and channel via band-gap engineering.…”