Structural Characterization of the Nanocolumnar Microstructure of InAlN

In x Al (1− x ) N (InAlN) thin films, lattice-matched to GaN with an In composition of ∼17%, are of interest for GaN-based devices. However, InAlN thin films grown by molecular beam epitaxy exhibit a characteristic lateral composition modulation, or nanocolumnar microstructure, with an Al-rich center region and an In-rich boundary. The mechanism driving the formation of this microstructure remains unknown. To date, the structural characterization of the nanocolumn domain size and its associated compositional variation is challenging, requiring either transmission electron microscopy or atomic probe microscopy. We show that the nanocolumnar microstructure can be characterized using x-ray diffraction and is associated with increased diffuse scattering. Using this technique, we show that the development of the microstructure is dependent on growth temperature.