Physics of degradation in GaAs-based heterojunction bipolar transistors

The GaAs HBT has recently become the technology of choice in particularly demanding wireless communications applications. However, controversy about HBT reliability is still widespread, with conflicting claims for lifetime and activation energy. Here, we detail the fundamental physics of HBT degradation, and describe the stress factors that drive it. Extensive testing shows that degradation is typically due to the formation of midgap traps associated with crystalline defects in the base. In addition, we describe the physical reasons for the superiority of the GaInP emitter in reliable HBT design. Finally, we show preliminary results of a stress test on large area (2 x 45 (mu)m^2 GaInP emitter HBTs which have lasted 5000 hours at 75 kA/cm^2, 215 °C with no discernable degradation in device characteristics yet. © 1999 Elsevier Science Ltd. All rights reserved.