TABLE OF CONTENTS This chapter will cover most of the basic active processing steps in GaAs heterojunction bipolar transistors. The active steps are those that are related to processing the GaAs and whose nuances require an understanding of the GaAs semiconductor surface and its interface to metal junctions for etching and contact formation. HBTs present many active processing subtleties with important implications for device design and operation. A clear understanding of how GaAs surface technology impacts HBT design and operation is a major objective in the presentation of this chapter's subject matter.
The basics of bipolar transistors and HBT operation and performance are given in Section 9.2. That section begins with a tutorial and continues to relate HBT operation to the main material and processing methods. It also highlights the main reliability issues and relates them to HBT structures, processing and materials. Sections 9.3, 9.4 and 9.5 present the details of the main active processing methods: mesa etching, ohmic metal formation and HBT passivation. In Section 9.6, alternative methods of HBT processing to enhance performance are summarised. Finally, specific HBT reliability and degradation issues are presented in Section 9.7.
The HBT is a type of bipolar transistor. Transistors are types of active or nonlinear devices in which the output response is modified in a nonlinear way from the input. The transistor was invented in 1947 at Bell Telephone Laboratories. Called a point-contact transistor and made from a piece of germanium with three wire contacts, it functioned more...
