Characterization of Quaternary AlxGa1-(x+y)InyN (x ≈ 0.5 and y ≤ 0.12) Metalorganic Vapor Phase Epitaxy Growth Focusing on Unintentionally Incorporated Impurities

Quaternary AlGaInN has attracted attention because its physical properties such as bandgap, polarization, and lattice constant can be independently changed by controlling the AlN, GaN, and InN mole fractions. However, the complexity of crystal growth is problematic, and reducing unintentionally incorporated impurities that cause carrier scattering and compensation is crucial. In this study, about 30-nm-thick AlxGa1-(x+y)InyN (x approximate to 0.5 and y <= 0.12) is grown on GaN on sapphire by metalorganic vapor phase epitaxy under various growth conditions to systematically analyze the relationship between growth conditions and oxygen and carbon concentrations ([O] and [C], respectively) as well as surface morphology and to elucidate the factors affecting [O] and [C]. [O] is decreased in samples grown at low growth rates and high growth temperatures. This can be attributed to the realization of a smooth surface morphology free of V-pits and trench defects. [C] is decreased in samples grown at a low total of group III source flow rates. The [C] of UID-GaN and that of AlGaInN at various TMI flow rates suggest that TMA mainly affects [C]. Therefore, the key to impurity reduction is to obtain a smooth surface morphology and to promote the adequate decomposition of TMA.