Heterojunction semiconductor device and method of manufacture

摘要

A heterojunction bipolar transistor (HBT) (30) is formed to have a germanium composition profile (46) in a base region (32) that improves the tolerance of the HBT device (30) to manufacturing variations and reduces the sensitivity to emitter/base biases. A first region (40) of essentially constant germanium composition is formed at the interface of an emitter region (34) and the base region (32). The germanium composition profile (46) also has a second region (41) in which the germanium composition is increased linearly to provide an acceleration field by reducing the band gap in this second region (41). The acceleration field reduces the transit time of carriers and increases the frequency response of the HBT device (30).