Germanium-based transistors for future high performance and low power logic applications

High mobility channel materials could replace strained Si to enhance speed performance and/or reduce power consumption in future transistors. Ge has the highest hole mobility among common elemental and compound semiconductors, and an electron mobility that is two times larger than that of Si. Ge is thus a promising channel material for future CMOS (Fig. 1). Key challenges include cost-effective integration of Ge on Si in a manufacturable process, formation of high-quality gate stack on Ge for n- and p-FETs at aggressively scaled EOTs that deliver high channel mobilities, and leakage issues related to its small bandgap. In this paper, we discuss recent research progress in advancing Ge-based transistor technologies. Integration of Ge on Si substrate to enable fabrication of high performance devices and formation of high-quality gate stack for Ge FETs (particularly for n-FETs) will be discussed. We also explore opportunities to boost the mobility of Ge, e.g. by incorporating Sn in Ge to form Ge_1-xSn_x. Furthermore, by raising the Sn composition, the band gap E_G of Ge_1-xSn_x becomes smaller and transits from indirect to direct, making Ge_1-xSn_x a promising material for tunneling transistors.