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 diffusion from the base into the collector, with the extent of diffusion depending on the n-doping level of the emitter. This behavior is explained in terms of nonequilibrium point defects induced by a combination of surface pinning of the Fermi level and n doping. It is also shown that the Zn diffusion can be substantially reduced by using AlInAs, instead 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 interstitials in AlInAs. Furthermore, it is shown that the introduction of only 50 nm of AlInAs between the n-InP emitter and p+-InGaAs base resulted in a significant reduction of Zn diffusion into the collector.