Luu The Vinh

The dimensional scaling of tunnel field-effect transistors (TFETs) is an indispensable issue to make them competitive with traditional metal-oxide-semiconductor field-effect transistors (MOSFETs). This paper elucidates the scalabilities of very potential TFETs utilizing Si/SiGe heterojunctions operated in n- and p-type operation modes. Although using the Si/SiGe heterostructures helps to improve the on-currents of both n- and p-type TFETs, its assistance in scaling the device dimension is essentially different between the n- and p-type modes. The asymmetric band-offset of Si/SiGe heterojunctions associated with the asymmetric properties of tunneling in n- and p-type TFETs are responsible for the scalability difference. With a high scalability down to sub-10 nm, the graded Si/SiGe heterojunction p-type TFET exhibits a feasible candidate for low-power and highly-scaled integrated circuits.

EFFECTS OF SOURCE DOPING PROFILE ON DEVICE CHARACTERISTICS OF LATERAL AND VERTICAL TUNNEL FIELD-EFFECT TRANSISTORS

The heterostructure technique has recently demonstrated an excellent solution to resolve the trade-off between on- and off-state currents in tunnel field-effect transistors (TFETs). This paper shows the weakness of abrupt heterojunctions and explores the physics of drive current enhancement as well as generalizes the proposed graded heterojunction approach in both n-type and p-type TFETs. It is shown that the presence of thermal emission barriers formed by abrupt band offsets is the physical reason of the on-current lowering observed in abrupt heterojunction TFETs. By employing graded heterojunctions in TFETs, the thermal emission barriers for electrons and holes are completely eliminated to narrow the tunnel widths in n-type and p-type TFETs, respectively. With the significant improvement in on-current, this novel approach of graded heterojunctions provides an effective technique for enhancing the drive current in heterostructure-based TFET devices.

The energy bandgap is a key factor to determine the tunneling current in tunnel field-effect transistors (TFETs). This paper numerically investigates the effect of quantum confinement in the double-gate TFETs by evaluating the effective energy-band bandgap of the ultra-thin strained-Si _1-x Ge _x body. The band-offset caused by the quantum confinement effect is rapidly increased with increasing the Ge mole fraction because the body thickness must be decreased to retain the same compressive strain of Si _1-x Ge _x . A medium Ge more fraction of strained-Si _1-x Ge _x is favorable to optimize the device performance in the strained-Si _1-x Ge _x double-gate TFETs.

Tunnel field-effect transistor (TFET) has served as one of the most attractive candidates for use in future low-power integrated circuits. To explore the current-voltage characteristics of TFET devices, the Kane's tunnel model has been widely used in numerical simulations and physical models to predict the tunneling current produced in the TFETs. This study examines the proper calculations of Kane's model parameters appropriate for the indirect band-to-band tunneling generated in compressively strained Si _1-x Ge _x channel on Si-substrate. The calculated parameters were verified with the measured results from experimental TFETs. Good agreements are confirmed between the numerical and measured data without any fitting factors.