Realization of low dislocation density AlN on a small-coalescence-area nano-patterned sapphire substrate.

Growth behaviors of AlN on hexagonal configuration hole-type and truncated-cone-pillar-type nano-patterned sapphire substrates (NPSSs) have been investigated. It is found that threading dislocation density (TDD) of AlN grown on the hole-type NPSS reaches 4.87 × 10⁸ cm⁻², which is over one order of magnitude lower than the value 6.63 × 10⁹ cm⁻² on the pillar-type one with the same period and mesa width. It is verified that the TDD of AlN grown on NPSSs is greatly dominated by the area ratio of the coalescence zones and thus the NPSS pattern with a small coalescence area (SCA) ratio is the preferred choice for high-quality AlN epitaxy. Benefiting from the low-TDD AlN grown on the hole-type NPSS with an SCA, the internal quantum efficiency of the 281 nm AlGaN-based multiple quantum wells has reached 73.9% at 300 K. [ABSTRACT FROM AUTHOR]