Design of GeSn-Based Heterojunction-Enhanced N-Channel Tunneling FET With Improved Subthreshold Swing and ON-State Current
We design a heterojunction-enhanced n-channel tunneling FET (HE-NTFET) employing a Ge<sub>1-x</sub>Sn<sub>x</sub>/Ge<sub>1-y</sub>Sn<sub>y</sub> (x > y) heterojunction located in the channel region with a distance of L<sub>T-H</sub> from the source-channel tunneling junction. We investigate the impact of L<sub>T-H</sub> on the performance of HE-NTFETs by simulation. HE-NTFETs achieve a positive shift of VONSET, a steeper subthreshold swing (SS), and an enhanced ION compared with homo-NTFETs, which is attributed to the modulating effect of heterojunction on band-to-band tunneling (BTBT). At a supply voltage of 0.3 V, 304% ION enhancement is demonstrated in the Ge<sub>0.92</sub>Sn<sub>0.08</sub>/Ge<sub>0.94</sub>Sn<sub>0.06</sub> HE-NTFET with a 4 nm L<sub>T-H</sub> over Ge0.92Sn0.08 homo-NTFET due to the steeper average SS. The impact of Sn composition on the performance of HE-NTFETs is also studied. As we increase the difference in Sn composition x - y across the heterojunction, ION and SS of HE-NTFETs are improved due to the increase in band offsets at the Ge<sub>1-x</sub>Sn<sub>x</sub>/Ge<sub>1-y</sub>Sn<sub>y</sub> interface, which leads to the enhanced modulating effect of heterojunction on BTBT.