TABLE OF CONTENTS In addition to the SiGe-HBTs and HFETs discussed in Chapters 5 and 6, considerable work has been done on other SiGe heterostructures. Notable among them are modulation doped field effect transistors, resonant tunnel diodes (RTDs), BICFETs and various optical devices. The MODFET will be covered in Chapter 8 while Si/SiGe optoelectronic devices will be presented in Chapter 10. RTDs and BICFETs are discussed in this chapter. Although many other devices have been reported using SiGe strained layers, the work that has been done is not extensive and their performances have not yet reached a high level.
Taylor and Simmons [1] proposed the bipolar inversion channel field effect transistor as a device that would fulfill both the speed requirements and the future needs of scaled devices. It is a three-terminal device, which, although a bipolar transistor in nature, relies upon an inversion channel charge to control current flow. The devices were first fabricated using GaAlAs/GaAs and InGaAs/InAlAs. This concept removed the problems associated with a finite base layer used in a conventional bipolar junction transistor. However, because the influence of the inversion charge on the thermionic barrier and majority carrier flow is strong, the transconductance of the device still maintains the exponential behavior of the BJT. The BICFET has electrical characteristics that are very similar to the BJT. The major difference is that the base hole concentration of the BICFET is very dynamic with respect to applied bias. At low bias the resistance is very high,...
