Current status of GaN heterojunction bipolar transistors

This paper reviews the current state-of-the-art GaN HBT results, and discusses the advantages of GaN HBTs over GaN HFETs and other material systems for high power amplifier applications. Technical difficulties associated with GaN HBTs such as MOCVD material growth, ICP dry etching, and ohmic contact issues are discussed. Methods for the elimination of technical issues and the authors' recommended approaches for practical realization of the GaN HBT-based RF high power amplifiers are described.