Pulsed-flow growth of polar, semipolar and nonpolar AlGaN
The impacts of pulsed-flow growth on aluminium incorporation in polar (0001), semipolar (10-13) and (11-22), as well as nonpolar (10-10) AlGaN layers have been investigated. The layers were grown simultaneously on differently oriented AlN/sapphire templates by metal-organic vapour phase epitaxy. The AlN mole fraction (0 < xAlN ≤ 0.85) of the layers was varied by simply changing the supply time of aluminium precursor while keeping nitrogen and gallium precursors constant. Phase separation has been observed for the (0001) and (11-12) layers by x-ray diffraction, which is attributed to their different surface reconstructions during growth. In contrast, no phase separation has been observed for the (10-10) and (10-13) layers, attributed to their stable surfaces during growth. The AlN mole fraction of the differently oriented layers generally follows the order: (11-22)<(0001)<(10-13)≤(10-10), attributed to their different surface dangling bonds. By means of room-temperature luminescence measurements, highly carbon-incorporation has quantitatively been found in all the layers.