High performance Si and SiGe-base pnp transistors

Abstract

Heterojunction pnp 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 pnp transistors fabricated in silicon technology.