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Single-crystal semi-polar (112¯2) AlN films are grown on 2-inch m-plane sapphire substrates by high-temperature hydride vapor phase epitaxy (HVPE). The introduction of the sapphire nitridation pretreatment and low-temperature AlN buffer layer suppresses the formation of undesired (101¯3) and (101¯1) AlN, leading to the desired single-crystal (112¯2) AlN film. The high growth temperature promotes a shift in growth mode from three-dimensional islands to two-dimensional step flow. This facilitates grain coalescence, resulting in the formation of well-defined macro steps on the (112¯2) AlN surface. The 9.02 μm-thick (112¯2) AlN film exhibits excellent crystalline quality, as evidenced by the narrow full widths at half maximum of 547′′ and 634′′ for the X-ray rocking curves measured along the [112¯3]AlN and [11¯00]AlN directions, respectively. The surface of the 2-inch (112¯2) AlN film is free of cracks and unmerged grains, providing a suitable substrate for the subsequent epitaxial growth of (112¯2) AlN light emitter layers. [ABSTRACT FROM AUTHOR]

Smooth and crack-free (0002) AlN thick films (∼30 μm) were epitaxially grown on trench-patterned AlN/sapphire templates through epitaxial lateral overgrowth (ELO) using hydride vapor phase epitaxy. The trenches on AlN/sapphire templates were oriented along [10−10]AlN, where the width of terraces and grooves was 8 μm and 4 μm, respectively. A comprehensive study was conducted on the influence of growth pressure on the morphology, crystal quality, and residual stress of the AlN thick films. As the growth pressure decreased from 40 torr to 20 torr, the lateral-to-vertical growth rate ratio of AlN increased, facilitating faster coalescence of separated AlN terraces to form a continuous film. Triangular voids were formed during the coalescence of AlN terraces, with the largest void size being observed at 20 torr due to the fastest coalescence. These triangular voids prevented the propagation of threading dislocations into the epitaxial layer, promoting their merging into loops and annihilation, while also releasing residual stress in the AlN film. As the growth pressure decreased, these triangular voids gradually became larger, accompanied by a reduction in etch pit density and residual stress in the AlN film. Compared to the initial AlN/sapphire template, the etch pit density of the AlN thick film grown by ELO at 20 torr decreased from 1.1 × 108 cm−2 to 3 × 107 cm−2, while the residual stress was reduced from 1.4 GPa to 0.4 GPa. [ABSTRACT FROM AUTHOR]

AlN epilayers were grown on magnetron-sputtered (MS) (11–22) AlN buffers on m-plane sapphire substrates at 1450 °C via hydride vapour phase epitaxy (HVPE). The MS buffers were annealed at high temperatures of 1400–1600 °C. All the samples were characterised using X-ray diffraction, atomic force microscopy, scanning electron microscope and Raman spectrometry. The crystal quality of epilayers regrown by HVPE was improved significantly compared to that of the MS counterpart. With an increasing annealing temperature, the crystal quality of both MS buffers and AlN epilayers measured along [11–23] and [1–100] improved first and then decreased, maybe due to the decomposition of MS buffers, while the corresponding anisotropy along the two directions decreased first and then increased. The optimum quality of the AlN epilayer was obtained at the annealing temperature of around 1500 °C. In addition, it was found that the anisotropy for the epilayers decreased significantly compared to that of annealed MS buffers when the annealing temperature was below 1500 °C. [ABSTRACT FROM AUTHOR]