Indium bilayer mediated InGaN surface decomposition: A comprehensive phenomenological model of epitaxial kinetic mechanisms

Indium gallium nitride ternary alloys constitute an important semiconductor material class valued for their broad applicability arising from their tunable direct bandgaps that cover the entire spectrum from ultraviolet to near-infrared. Achieving high-quality growth requires a thorough understanding and control of the dominant surface kinetic mechanisms active during the epitaxial process. In this Letter, the epilayers' decomposition process during molecular beam epitaxy was investigated in the relevant growth temperature range of 470–570 °C. Contrary to expectations, the decomposition rate was found to be independent of the films' composition but highly dependent on the indium bilayer coverage of the growing surface, revealing a catalytic role for the indium adlayer. A phenomenological description of the decomposition rate, as a function of incident atom fluxes, during epitaxial growth, under full bilayer coverage, is derived. Including indium desorption kinetics, a comprehensive model of InGaN molecular beam epitaxial growth is obtained that aligns with experimental data for both full and partial surface coverage conditions. The activation energy of the indium bilayer-catalyzed decomposition mechanism was measured at 0.671 ± 0.021 eV, significantly lower than that for bulk decomposition, underlying its dominant role during epitaxy. Beyond clarifying the complex alloy phase diagram and offering the tools to tune epitaxial conditions for composition-tailored high-quality epilayers, the model offers key insights into transient phenomena, important for the realization of optimized InGaN heterostructures.