Strained Si Heterojunction Bioploar Transistors

Abstract

This dissertation addresses the world’s first demonstration of strained Si Heterojunction Bipolar Transistors (sSi HBTs). The conventional SiGe Heterojunction Bipolar Transistor (SiGe HBT), which was introduced as a commercial product in 1999 (after its first demonstration in 1988), has become an established device for high-speed applications. This is due to its excellent RF performance and compatibility with CMOS processing. It has enabled silicon-based technology to penetrate the rapidly growing market for wide bandwidth and wireless telecommunications once reserved for more expensive III–V technologies. SiGe HBTs is realised by the pseudomorphic growth of SiGe on a Si substrate, which allows engineering of the base region to improve performance. In this way the base has a smaller energy band gap than the emitter, which increases the gain. The energy band gap of SiGe reduces with increasing Ge composition, but the maximum Ge composition is limited by the amount of strain that can be accommodated within a given base layer thickness. Therefore, a new innovation is necessary to overcome this limitation and meet the continuous demand for high speed devices. Growing the SiGe base layer over a relaxed SiGe layer (Strain Relaxed Buffer) can increase the amount of Ge that can be incorporated in the base, hence, increasing the device performance. In this thesis, experimental data is presented to demonstrate the realisation of sSi HBTs. The performance of this novel device has been also investigated and explained using TCAD tool.