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We report on the MOVPE of ZnTe in two typical reactor geometries. Horizontal flow in rectangular tubes with even and tilted susceptors are compared with axisymetric vertical downward flow arrangements on even (horizontal) and tilted susceptors. Growth parameters such as temperature and input partial pressures of the Zn and Te precursors are studied. The growth with the precursors diethylzinc (DEZn) and dimethylzinc-triethylamin (DMZn-TEN) in various combinations with the Te-alkyls diethyltelluride (DETe), diisopropyltelluride (DIPTe) and methylallyltelluride (MATe) is discussed. The hydrodynamics of the reactors are characterised by dimensionless numbers. Analytical and numerical simulation of the mass transport supports the interpretation of growth results. Furthermore, a simple reaction boundary layer model has been developed. The model is especially useful for a first estimation of the contribution of gas phase dissociation to the growth. Catalytic dissociation of precursors was found to play an essential role in the growth process. Analytical models of the surface processes are discussed. The kinetic entrance zone in horizontal reactors has a strong influence on the mass transport limited growth rates. Gas phase nucleation and particle growth cause severe problems under certain circumstances. Finally, a complete picture of ZnTe-MOVPE is developed including all the main aspects of hydrodynamics and mass transport, chemical kinetics and the thermodynamic description of the growth process. We will point out that the correct interpretation of growth phenomena often presumes an understanding of all main aspects of MOVPE growth as flow, temperature and concentration fields, mechanisms and kinetics of the source decomposition, surface processes, supersaturation and nucleation phenomena, which are often not well enough known. |
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