Zn diffusion behavior in InP/InAlGaAs heterojunction bipolar transistors and light emitting transistors grown by metalorganic chemical vapor deposition was investigated. Using secondary ion mass spectrometry, the Zn doping profiles in the epitaxial structures were studied in relation to their growth conditions. Migration of Zn atoms from the base layer was found to be a combined result of three mechanisms, i.e. the generation of excess group III interstitials during the n-type InP subcollector growth, the generation of Zn interstitials in the Zn-doped InAlGaAs base, and the presence of strong electric field at the emitter-base n-p junction. By choosing the growth conditions either to suppress or to enhance the effects of each mechanism, Zn is able to diffuse either in both directions into the adjacent emitter and collector, or forward only into the emitter, or backward only into the collector. An abrupt junction profile, with the suppression of Zn diffusion, in the InP:Si/In(Al0.25Ga0.75)As:Zn/InAlAs:ud/InP:Si light emitting transistor structure has been achieved by low Si doping in the InP subcollector, low temperature growth of the InAlGaAs base, and slightly high Si doping in the InP emitter. (C) 2008 Elsevier B.V. All rights reserved.