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(a) Cross-sectional SEM micrograph of a fully coalesced thick AlN film grown by MELEO technique. The dotted lines outline AlGaN mesa profile. (b) Bird’s eye view image of the MELEO-grown film illustrates the smooth and uniform top surface. (c) SEM micrographs of a fully coalesced thick AlN film grown by conventional approach. The top surface reveals surface undulations. (b) Cross-sectional image shows incoherent coalescence.
Simplified schematic representation of the effect of growth conditions on the wing tilt and the coalescence. 1: sapphire, 2: AlGaN mesa, 3: AlN growth on AlGaN mesas, 4: parasitic growth in trenches, 5: voids, 6: incoherent coalescence. (a) Continuous faster growth in lateral direction results in tilted growth fronts, leading to coalescence of crystallographically misaligned domains. (b) Reducing the lateral growth rate and delaying the coalescence produces domains, which are oriented in ⟨0001⟩ direction. The MELEO conditions lead to coherent coalescence of such domains.
Relative optical power as a function of time for DUV LED under CW. The extrapolated operation lifetime is estimated to be in excess of . The inset shows initial power vs current characteristic of a packaged LED.
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