Comparison of H+ and He+ implant isolation of GaAs-based heterojunction bipolar transistors

The use of multiple energy He+ implantation for producing electrical isolation between neighboring GaAs/AlGaAs or GaAs/InGaP heterojunction bipolar transistors is found to alleviate the problem of time-dependent current gain behavior found in H+ isolated devices. This latter phenomenon is ascribed to rapid diffusion of atomic hydrogen into the active base region during the anneal required to maximize the resistance of the implanted areas, and the subsequent reactivation of passivated C acceptors in the base. Replacement of H+ with He+ ions in the implant scheme produces similar high resistance isolation regions (≳108 Ω/cm) without the presence of hydrogen passivation effects.