Unintentional Zn diffusion during metalorganic vapor phase epitaxy causes serious damages in semiconductor devices. In this work, profiles of unintentionally diffused Zn atoms from a p-InP layer to the adjoining InP substrate during growth of the p-InP layer are measured by secondary ion mass spectrometry. Zn diffusion profiles with a double diffusion front, which is composed of a shallow front with high Zn concentration and a deep front with low Zn concentration, are investigated as an approach to controlling unintentional diffusion. Diffusion depth of each front is controlled in proportion to Zn dosage, which is proposed as a value calculated as Zn concentration without regard to saturation limit. The diffusion depth for the growth time of 60 min increases in proportion to the Zn dosage as the slope of 0.16 μm/1018 cm-3 for the shallow front and that of 0.32 μm/1018 cm-3 for the deep front at a growth temperature of 600 °C. The deep front expands two times faster than the shallow front, which is normally observed as a p-n junction. Zn concentration at which unintentional Zn diffusion occurs is determined to be more than 2 ×1017 cm-3. Therefore, the penetration of Zn atoms into the active region of semiconductor devices should be observed when unintentional diffusion takes place. Furthermore, even at low Zn concentration, the introduction of a kick-out mechanism is proposed to explain the diffusion coefficient of the unintentional diffusion. © 1998 American Institute of Physics.