Some fundamentals of the vapor and solution growth of ZnSe and ZnO

Some fundamentals of ZnSe and ZnO vapor and solution growth are investigate d. Residual water present in gases or gaseous mixtures such as H-2, Ar or H -2 + H2O is shown to act as a sublimation activator in the vapor-phase tran sport of both compounds. The processes involved in the growth by chemically activated sublimation with such gases and-gas mixtures have been studied b y close-spaced vapor transport (CSVT). The ZnSe growth rate is found to be constant, while in the ZnO case a high initial growth rate is followed by s lower growth subsequently. Using a theoretical model, the thermodynamic con stants of the transport - energies of activation, sublimation and condensat ion and enthalpy of formation - are determined independently from a fit to the variation of the growth rate as a function of the substrate temperature . No classical chemical transport reactions are shown to correspond to the sublimation mechanism, that is supposed to be chemically assisted by residu al water. In the case of ZnO, the sublimation mechanism is found to be more complex than for ZnSe, as expressed by the variation of the growth rate wi th time. As an alternative to this chemically assisted sublimation, chemica l vapor transport using chlorine as chemical agent is proposed for ZnO. Sig nificant transport is found to occur at temperatures of about 1000 degrees C. Concerning solution-growth, the pseudo-binary PbCl2-ZnO phase diagram es tablished by differential thermal analysis (DTA) shows PbCl2 to be a good s olvent of ZnO, as for ZnSe. Zn-In alloys are proposed as good alternative s olvents for ZnO not having the great reactivity of the PbCl2-ZnO mixture wi th silica. (C) 1999 Elsevier Science B.V. All rights reserved.