High performance Si and SiGe-base p-n-p transistors

Heterojunction p-n-p transistors with SiGe bases have been fabricated. Molecular beam epitaxy (MBE) was used to deposit both Si and SiGe bases, and the emitter was formed by low-temperature epitaxy. The base thickness of the SiGe-base transistor, as measured by secondary ion mass spectrometry, is less than 70 nm. The current gain of the SiGe-base device is 20 at room temperature and increases with decreasing temperature. Preliminary high-frequency measurements of small-geometry transistors have established a cutoff frequency of 10 GHz for the Si-base and above 12 GHz for the SiGe-base transistors. These are believed to be the fastest bipolar p-n-p transistors fabricated in silicon technology.<>