Origins of unintentional incorporation of gallium in AlInN layers during epitaxial growth

Abstract

We propose a mechanism of unintentional gallium (Ga) incorporation during the epitaxial growth of AlInN layers. We observed substantial amount of Ga in AlInN layers on GaN-free underlying layers and wafer carrier grown by metalorganic chemical vapor deposition, even though the Ga precursor was not introduced during the growth. The AlIn(Ga)N layers were characterized by high-resolution X-ray diffraction and Rutherford backscattering spectrometry. The mole fraction of Ga in the AlIn(Ga)N layers showed strong dependence on conditions of the growth chamber, making it difficult to maintain controlled alloy compositions only by growth process parameters. Also, Ga incorporation was not observed under the same growth parameters and conditions, when the indium (In) precursor was absent. The formation of In-Ga eutectic system between metallic Ga from the deposition on the chamber surrounding surfaces and adsorbed In is suggested as a possible mechanism for the Ga incorporation. Finally, we performed an intentional chamber coating process prior to growth of AlInN to achieve repeatable AlIn(Ga)N growth with stable alloy compositions.