Current Degradation by Carrier Recombination in a Poly-Si TFET With Gate-Drain Underlapping

The drain lapping effect of tunneling FETs (TFETs) with polycrystalline-silicon (poly-Si) channel film is well investigated for the first time. The carrier transport mechanisms of poly-Si TFETs can be divided into several transportmechanisms due to the device structure of source to drain. The interband tunneling at source/channel junction, carrier drift in the channel region, and drain-to-gate underlap region are elemental carrier transport mechanisms of TFETs with single-crystalline channel material. The poly-Si channel has many grain boundary trap states among bandgap due to the grain boundary defects, resulting in strong recombination effect in the drain-to-gate underlap region of poly-Si TFETs. The recombination rate of the underlap region would be significantly enhanced with the increased temperature and lead to obvious ON-state current (I-ON) degradation. Therefore, the I-ON behavior of the drain lapping effect is sensitive to the temperature and underlap length. In addition, the poly-Si TFETs with drain-to-gate overlap structure exhibit less temperature dependence and drain-to-gate overlap length dependence of the I-ON to exhibit stable electrical behavior. Consequently, the drain lapping structure of poly-Si TFETs would trade the suppression of ambipolar behavior of poly-Si TFETs by the drain-to-gate underlap structure off against the I-ON instability of temperature and device dimension.