Silicon has enabled the rise of the semiconductor electronics industry, but it was not the first material used in such devices. During the 1950s, just after the birth of the transistor, solid-state devices were almost exclusively manufactured from germanium. Today, one of the key ways to improve transistor performance is to increase charge-carrier mobility within the device channel. Motivated by this, the solid-state device research community is returning to investigating the high-mobility material germanium. Germanium-based transistors have the potential to operate at high speeds with low power requirements and might therefore be used in non-silicon-based semiconductor technology in the future.
Figure 1: The mobility landscape of semiconductors.
The bulk mobility is plotted against the bandgap for silicon, germanium and a variety of group III–V materials. Filled symbols indicate electrons, and open symbols indicate holes. Germanium offers the highest hole mobility of any known…
Figure 2: The integration of germanium on silicon.
A cross-sectional scanning electron microscopy image of germanium-on-silicon growth, using the aspect-ratio-trapping process. Scale bar, 0.25 μm. Reproduced, with permission, from ref. STI, shallow-trench isolation.
