Influence of Gas Mixing and Heating on Gas-Phase Reactions in GaN MOCVD Growth

The controversies about gas phase reaction path in GaN MOCVD process are investigated with emphasis on the reactions after adduct formation. Different gas mixing and heating approaches in the reactor inlet are proposed to be the cause that lead to three different reaction paths: if mixing occurs at room temperature and heating is gradual (long residence time), the reversible dissociation of adduct TMG:NH3 into TMG and NH3 will dominate, followed by TMG pyrolysis when further heated (Path 1); if mixing occurs at "warm" temperature (200 similar to 500 degrees C) and heating is rather fast (short residence time), the irreversible adduct decomposition to form amide DMGNH(2) or amide-derived particles will occur (Path 2); if mixing occurs at "hot" temperature (>500 degrees C), and heating is very fast (very short residence time), direct pyrolysis of TMG will be the dominant reaction path (Path 3). Numerical simulations for typical MOCVD reactors have verified that, in the vertical reactor with long reactor height the reactions will follow Path 1; in the premixed horizontal reactor both Path 1 and Path 2 exist, with Path 1 dominating the vicinity of susceptor and Path 2 dominating the vicinity of ceiling; and in the close spaced showerhead reactor the dominant reaction path will be Path 3. (C) 2012 The Electrochemical Society. All rights reserved.