Indium incorporation and optical properties of polar, semipolar and nonpolar InAlN

Indium incorporation and the optical properties of InxAl1-xN layers (0 <= x <= 0.45) grown by metalorganic vapour phase epitaxy have been investigated simultaneously on polar (0001), untwinned semipolar (10 (1) over bar3) and nonpolar (10 (1) over bar0) AlN templates, which were prepared on planar sapphire substrates. The InN mole fraction (x(InN)) of the layers was tuned by changing growth temperature from 660 degrees C to 860 degrees C. x(InN) determined by x-ray diffraction was found to be comparable for the polar, semipolar and nonpolar surface orientations. This is consistent with comparable effective bandgap energy of the layers obtained from optical transmission measurements at room temperature. The bandgap bowing parameter was found to be strongly composition-dependent. Room-temperature photoluminescence measurements showed impurity transitions for the layers with x(InN) <= 0.2, while InAlN near-band-edge luminescence was observed for the layers with higher x(InN).