Improving AlN Crystal Quality and Strain Management on Nanopatterned Sapphire Substrates by High‐Temperature Annealing for UVC Light‐Emitting Diodes

Herein, AlN growth by metalorganic vapor‐phase epitaxy on hole‐type nanopatterned 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 (HTA) of a 300 nm‐thick AlN starting layer is successfully introduced. By this method, 800 nm‐thick, fully coalesced and crack‐free AlN is grown on 2 in. nanopatterned sapphire wafers. The usability of such templates as basis for UVC light‐emitting diodes (LEDs) 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 nanopatterned sapphire substrates are discussed. Cracking during AlN growth by metalorganic vapor‐phase epitaxy on hole‐type nanopatterned sapphire substrates is prevented by high‐temperature annealing (HTA). At the same time, HTA allows the reduction of the threading dislocation density of the AlN by an order of magnitude. Such substrates are successfully used for UVC‐LED growth and compared with LEDs grown on templates with planar AlN/sapphire but similar threading dislocation density.