Hagedorn, S.; Walde, S.; Susilo, N.; Netzel, C.; Tillner, N.; Unger, R.-S.; Manley, P.; Ziffer, E.; Wernicke, T.; Becker, C.; Lugauer, H. - J.; Kneissel, M.; Weyers, M.: Improving AlN crystal quality and strain management on nano-patterned sapphire substrates by high temperature annealing for UVC-LEDs. Physica Status Solidi A 217 (2020), p. 1900796/1-7
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In this study, AlN growth by metalorganic vapor phase epitaxy on hole-type nano-patterned sapphire substrates is investigated. Cracking occurs for an unexpectedly thin layer thickness which is associated to altered nucleation conditions caused by the sapphire pattern. To overcome the obstacle of cracking and at the same time to decrease the threading dislocation density by an order of magnitude high temperature annealing of a 300 nm thick AlN starting layer is successfully introduced. By this method, we end up with 800 nm thick, fully coalesced and crack-free AlN on 2-inch nano-patterned sapphire wafers. The usability of such templates as basis for UVC light emitting diodes is furthermore proved by subsequent growth of an UVC-LED heterostructure with single peak emission at 265 nm. Prerequisites for the enhancement of the light extraction efficiency by hole-type nano-patterned sapphire substrates are discussed.