Selective Area Growth of GaN Using Polycrystalline gamma-Alumina as a Mask for Discrete Micro-GaN Array

For commercialization of micro-light-emitting diodes (micro-LEDs), which have been considered as a next-generation display technology, a novel growth template named sapphire nanomembrane was introduced by our research group previously. However, not only the growth condition but also the transfer of discrete micro-LEDs onto other substrates was limited due to the undesired growth at the bottom substrate region between the membranes. Here, we introduce a new selective area growth technology using amorphous alumina as a growth mask material. Because amorphous alumina consists of the same material with the sapphire substrate, it would not cause contamination or unintentional doping, which is occasionally caused by Si-based mask materials. During the growth of GaN using metal organic chemical vapor deposition, the surface region of an amorphous alumina layer, which was used as a growth mask, was crystallized into polycrystalline gamma-alumina through the "random nucleation and growth" process, while the other region crystallized into single-crystalline alpha-alumina through the "solid phase epitaxy" process. Thereafter, GaN hardly grew on polycrystalline gamma-alumina owing to the large difference in growth rates between GaN islands, which grew on different grains of polycrystalline gamma-alumina. Due to the suppressed growth of GaN on polycrystalline gamma-alumina, highly enhanced selective growth of the micro-GaN array on sapphire nanomembranes could be achieved.