Surface roughness of Gallium Nitride with Volcano-like Protrusions Formed by KrF Excimer Laser Etching

摘要

Use of deep ultraviolet (248 nm) KrF laser irradiation to roughen vertical GaN-based LEDs surface with volcano-like protrusions for light output (Lop) improvement was proposed and demonstrated. After pulse irradiations of KrF laser (750-850 mJ/cm~2), the rate of electron-hole pair recombination at sites with dislocation defects is greater than for crystalline GaN, favoring for the formation of GaO_x, and in turn, resulting in a relatively lower etching rate therein and leading to a roughened surface with volcano-like protrusions. Typical diameter/height and density of protrusions are around 2～4 μm/2 μm and 10~6 cm~(-2). Through the use of KrF laser and KOH etching, an enhancement in the root-mean-square surface roughness by 250 times and an improvement in Lop by 25% at 750 mA were obtained. It is expected that the surface roughness of Gallium Nitride by KrF excimer laser technology would be a potential candidate for the fabrication of high power GaN-based LEDs for solid-state lighting in the near future.