Effect of a Lateral Overgrowth Process on the Strain Evolution of AlN Films Grown on a Nanopatterned Sapphire Substrate for Ultraviolet‐C Light‐Emitting Diode Applications

Abstract

Strain evolution of AlN grown on hole‐type (HT) and pillar‐type (PT) nanopatterned sapphire substrates (NPSSs) during the epitaxial lateral overgrowth process is comparably studied. It is found that, after complete coalescence, the residual strain of AlN on HT‐NPSS is tensile, whereas AlN on PT‐NPSS is almost strain free. The different strain states are associated with different behaviors of crystal merging during the lateral overgrowth process, depending on the type of pattern. Then, ultraviolet‐C (UVC) light‐emitting diode (LED) wafers are grown on two types of AlN templates with the distinctive strain states. It is confirmed that AlN on HT‐NPSS with tensile strain offers the advantage of producing a high‐quality AlGaN layer with a fairly flat surface, which is the key point for fabricating high‐performance UVC LEDs.