AlGaAs/GaAs heterojunction bipolar transistors

Heterojunction bipolar transistors (HBTs) are one of candidates for future ultrahigh speed devices. However, there are many problems that must be overcome to realize high-speed HBTs for practical use. Major problems remain in the fabrication processes of HBTs, reduction of parasitic elements and suppression of current gain reduction associated with transistor size scaling down. To eliminate the problems, a new sidewall insulation structure, a new self-alignment process with dry-etching techniques and a graded base structure have been introduced.