The crystal growth of ZnO by vapour transport is classically made with the assistance of additional species that produce a gaseous mixture, the role of which remains often uncertain in the transport and growth processes. We have made a systematic study of the ZnO crystal growth process by vapour transport in presence of different additional species (Zn, C, H₂, Fe, Cu). Transport rates have been measured using an in-situ dynamic technique. The chemical role of each species has been analysed from the thermochemical point of view. It will be shown that, in some cases, additional species in the growth of ZnO by vapour transport promote the generation of an additional Zn pressure. This zinc pressure acts autocatalytically inducing O₂ and Zn partial pressures higher than those corresponding to the stoichiometric and equilibrium conditions at the sublimation interface. In addition we have made a numerical study of the process which shows that partial pressures higher than the equilibrium ones must be present in order to justify the experimental results. The experimental and numerical analysis, here shown, pave the way for new processes to promote the growth of ZnO by vapour transport; using controlled generation of additional Zn vapour as a mechanism to act on the growth and crystal properties.

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