Ge offers both better intrinsic hole mobility and better scalability compared to Si, reprinted with permission from. Hole mobility of Si and Ge as a function of stress and wafer orientation.

This suggests that if the challenges associated with Ge channel transistors can be overcome, the technology may continue to be scalable for decades. As seen in Figure 1, the hole mobility enhancement as a function of strain is much flatter in Si than for Ge. On the other hand, even with the change in device architecture from planar to F in FET, continued scaling of today’s Si transistors is expected to provide only a few additional generations of technology. The higher carrier mobility offered by these materials compared to strained silicon presents a practical means to push I on higher, even at lower supply voltages. In light of this relationship, future transistor scaling will require the introduction of new high mobility channel materials, including germanium (Ge) or III-V semiconductors. While this link has become less clear as devices are scaled down into quasi-ballistic and ballistic regimes, the general relation continues to hold. Saturation drive current ( I on), a critical performance metric for FET devices, is intimately linked with carrier mobility. The motivation to replace strained silicon (Si) with higher mobility channel materials in today’s metal-oxide-semiconductor field-effect transistors (MOSFETs) is well documented.

Germanium transistor