A study of Zn diffusion behavior in capped mesa buried heterostructure lasers reveals the Zn profile in the base epitaxial region of InGaAsP/InP heterostructures to be dominated by diffusion during regrowth. This diffusion behavior has enabled us to fabricate a laser without any Zn doping in the p clad during base growth. The lasing characteristics at 25 degrees C are comparable to those of normally Zn-doped structures. The Zn diffusion into the undoped cladding layer, and thus, the temperature performance of these lasers are dependent on the level of Zn doping in third growth. (C) 1998 American Institute of Physics.