Ge-on-insulator tunneling FET with abrupt source junction formed by utilizing snowplow effect of NiGe

Abstract

Tunneling field-effect transistors (TFETs) attract much attention for use in realizing next-generation low-power processors. In particular, Ge-on-insulator (GOI) TFETs are expected to realize low power operation with a high on-current/off-current (Ion/Ioff) ratio, owing to their narrow bandgap. Here, to improve the performance of GOI-TFETs, a source junction with a high doping concentration and an abrupt impurity profile is essential. In this study, a snowplow effect of NiGe combined with low-energy BF2+ implantation has been investigated to realize an abrupt p+/n Ge junction for GOI n-channel TFETs. By optimizing the Ni thickness to form NiGe (thickness: 4 nm), an abrupt junction with a B profile abruptness of ∼5 nm/dec has been realized with a high doping concentration of around 1021 cm−3. The operation of GOI n-TFETs with this source junction having the abrupt B profile has been demonstrated, and the improvement of TFET properties such as the Ion/Ioff ratio from 311 to 743 and the subthreshold slope from 368 to 239 mV/dec has been observed. This junction formation technology is attractive for enhancing the TFET performance.