REDUCTION OF ZINC DIFFUSION INTO THE COLLECTOR OF INP-BASED DOUBLE-HETEROJUNCTION BIPOLAR-TRANSISTORS GROWN BY ORGANOMETALLIC CHEMICAL-VAPOR-DEPOSITION

It is shown that the growth of emitter layers of InP/InGaAs/InP double heterojunction bipolar transistors can result in significant Zn diffu sion from the base into the collector, with the extent of diffusion de pending on the n-doping level of the emitter. This behavior is explain ed in terms of nonequilibrium point defects induced by a combination o f surface pinning of the Fermi level and n doping. It is also shown th at the Zn diffusion can be substantially reduced by using AlInAs, inst ead of InP, as the emitter layer. The difference in behavior is shown to be at least in part due to the lower diffusivity of group III inter stitials in AlInAs. Furthermore, it is shown that the introduction of only 50 nm of AlInAs between the n-InP emitter and p+-InGaAs base resu lted in a significant reduction of Zn diffusion into the collector.