Improving backside (N-face) GaN substrate roughening by pre-annealing for GaN-on-GaN LED

This work attempted to improve roughening on backside (N-face) of GaN substrate by increasing the density of hexagonal pyramids for enhanced GaN-on-GaN LED performance. Prior to the roughening by ammonium hydroxide-based etching, the substrate was annealed in two different ambiences; air and oxygen. After the roughening, the hexagonal pyramids with a density of 4.3 × 1010 cm−2 were formed on the substrate with oxygen pre-annealing. For the substrate with air pre-annealing, the hexagonal pyramids density was 2.0 × 1010 cm−2. Meanwhile, the pyramids density for the roughened GaN substrate without pre-annealing was 0.5 × 1010 cm−2. The oxygen pre-annealing introduced more Ga–O compound on the surface. This increased the density of hexagonal pyramids, which resulted after the etching. The GaN-on-GaN LEDs grown on the roughened GaN substrates with pre-annealing (air and oxygen) emitted at 488 nm, while the LED on the roughened GaN substrate without pre-annealing at 510 nm. The optical power increased significantly when the LED grown on the roughened GaN substrate with the oxygen pre-annealing. Overall, this work revealed that the backside GaN roughening can be improved by oxygen pre-annealing, leading to enhance the GaN-on-GaN LED performance.