Zinc Incorporation and Diffusion In InP During AP-MOCVD Growth

Despite the difficulty in controlling its doping profile, zinc is still the acceptor of choice for most InP/InGaAsP based photonic and electronic devices. We have systemically studied the incorporation and diffusion of zinc during atmospheric pressure metalorganic vapor phase deposition (AP-MOCVD) process. We used a surface adsorption-trapping model to analyze the incorporation kinetics and demonstrate that the Langmuir state of adsorption-desorption process for each surface layer has not been established before the growth of the subsequent layer during normal epitaxy. The observed saturation level at a given growth condition further indicates that Zn atoms incorporate at surface defect sites instead of the normal growth sites for In. The nature of these surface defect sites can be characterized by their capture cross-section and the time of desorption for Zn atoms. The implication of these parameters and the effect of temperature and substrate orientation are discussed. We have also studied Zn diffusion into the underlying undoped InP layer during the epitaxial growth of Zn-doped InP with different Zn doping concentration in order to investigate the concentration dependent Zn diffusion in light of interstitial-substitutional diffusion mechanism. A third power dependence of the diffusivity on the Zn source concentration is confirmed, indicating a +2 charge state for interstitial Zn in InP. The general agreement with the published results in different concentration regimes is discussed.