Overview

During the last fifteen years, extensive research has been conducted on various aspects of strained SiGe films: growth, transport, devices, and circuits. Major emphasis has been on the hetero junction bipolar transistors where a thin SiGe epitaxial layer has been used as a low bandgap semiconductor in the base. Indeed, SiGe-HBTs have demonstrated excellent high frequency performance with unity current gain cutoff frequency and maximum oscillation frequency exceeding 150 GHz. While SiGe-HBTs have been developed for application in wireless products for personal communication systems and circuits based on SiGe-HBTs are now commercially available, relatively little effort has been given towards enhancement of field effect devices.

Fabrication and performance of silicon-based heterostructure field effect transistors which are compatible with mainstream Si 1C have been described in Chapter 6. It has long been established that the best performance of FETs is obtainable in modulation doped devices [1] where the channel and the dopant layers are separated. This chapter discusses the fabrication techniques, dc and high frequency performance of modulation doped field effect transistors. The prospect of combining heterostructure p-and n-type devices for realizing heterostructure complementary MOS (HCMOS) devices which retain the advantages of Si CMOS at a higher level of performance has been a very active area of integration.

In this chapter, an overview of the concept of modulation doping, reported results for SiGe channel p-MODFETs, strained Si n-and p-MOSFETs and MODFETs will be presented. Issues related to material growth and the electrical transport properties of both electrons and holes in...