A Ge Ultrathin-Body n-Channel Tunnel FET: Effects of Surface Orientation
A Ge Ultrathin-Body n-Channel Tunnel FET: Effects of Surface Orientation
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DOI：
10.1109/ted.2014.2353513
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发表时间：
2014-09
影响因子：
3.1
通讯作者：
K. Alam;S. Takagi;M. Takenaka
中科院分区：
文献类型：
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作者：
K. Alam;S. Takagi;M. Takenaka
我们从理论上研究了表面取向对5 nm超薄体锗n沟道双栅隧道场效应晶体管复杂能带结构和性能的影响。Ge是间接带隙材料，并且Ge中的直接带间（BTB）隧穿率不被理解。用（001）和（011）Ge薄体将X[001]和X[100]谷投影到二维布里渊区中心，用（111）Ge薄体将L[111]谷对投影到二维布里渊区中心。虚k轴的运动轨迹是直接BTB隧穿的关键因素，我们发现（111）Ge薄体投影L[111]谷的虚k轴在三个取向中提供了最好的BTB隧穿率。（111）晶向的直接带隙最小，是（111）器件中最薄的隧道势垒。（111）器件的驱动电流比（011）器件高4倍，比（001）器件高15倍。（001）、（011）和（111）器件的亚阈值斜率显著低于热极限，然而，只有（111）器件的I60（60 mV/十倍斜率下的电流）值接近所需极限。在漏区采用低高斯掺杂来抑制双极电流。低5倍的掺杂导致漏-沟道界面处的隧道势垒长2倍，并且双极电流抑制超过两个数量级。
We theoretically investigated the surface orientation effects on the complex band structures and performance of a 5-nm ultrathin-body Ge n-channel double gate tunnel field-effect transistor. The Ge is an indirect bandgap material, and the direct band-to-band (BTB) tunneling rate in Ge is not appreciated. We use (001) and (011) Ge thin-body to project the X[001] and X[100] valley to the 2-D Brillouin zone center, and (111) Ge thin-body to project the L[111] valley pair to the zone center. The trajectory of imaginary k is the key factor for direct BTB tunneling, and we find that the imaginary k-axis of the projected L[111] valley of (111) Ge thin-body provides the best BTB tunneling rate among the three orientations. The direct bandgap of (111) orientation is lowest among the three orientations, which results in the thinnest tunnel barrier in (111) device. The drive current of (111) device is 4× higher than (011) device and 15× higher than (001) device. The (001), (011), and (111) devices have subthreshold slope substantially lower than thermal limit, however, only (111) device has an I60 (current at 60 mV/decade slope) value close to the desired limit. We use lower Gaussian doping in drain region to suppress ambipolar current. A 5× lower doping results in a 2× longer tunnel barrier at the drain-channel interface and more than two orders of magnitude suppression of ambipolar current.