The metal organic vapour phase epitaxy of ZnTe: I. Properties and decomposition kinetics of organometallics

Abstract

The growth of high quality II-VI devices by MOVPE is dependent upon the progress achieved in certain key research activities. Here, the precursors are the crucial point for a successful epitaxy. The metallorganics Et 2Te, iPr 2Te, MeTe-allyl, Et 2Zn, Me 2Zn and the Me 2Zn-Et 3N adduct are used for the growth of ZnTe epilayers. The relevant properties of these alkyls such as purity, vapour pressures, RT-stability and bond disruption energies are discussed. Special emphasis is put on the thermal decomposition. Reaction mechanisms and kinetics were studied in an isothermal ersatz reactor and by mass spectroscopy. Literature results are quoted to complete the interpretation. The evaluation of the measurements is often complicated due to the condensation and autocatalysis. Homogeneous and heterogeneous pyrolysis compete with each other ( iPr 2Te). Homolysis followed by radical reactions is the dominant reaction mechanism for Me 2Zn, Et 2Zn and MeTe-allyl. β-hydrogen elimination competes with homolysis in certain cases (Et 2Te, iPr 2Te). For most precursor combinations, strong interactions in pyrolysis are observed. For the relatively stable Te-alkyls Me 2Te and Et 2Te, the decomposition is enhanced by co-pyrolysis with Et 2Zn. For the less stable Te-alkyls iPr 2Te and MeTe-allyl, the decomposition kinetics remain essentially unchanged with Et 2Zn. The activation energies and prefactors for the elemental reaction steps are discussed. Basic considerations lead to an expression which allows the evaluation of E a for the surface reaction in a flow tube. Under similar experimental conditions, activation energies for the surface pyrolysis were found to be comparable to the growth activation energies.