Chemical etch characteristics of N-Face and Ga-Face GaN by phosphoric acid and potassium hydroxide solutions

We report the chemical etching characteristics of Ga-face and N-face GaN using phosphoric acid (H ₃PO ₄) or potassium hydroxide (KOH) solutions. Hexagonal pyramids, which consisted of the {10-1-1} planes, were present on the N-face after KOH (2M, 100C) etching. By contrast, using the H ₃PO ₄ (85 wt., 100C) solutions, the nitrogen surface of GaN showed dodecagonal pyramids. Dodecagonal and hexagonal pyramids repeatedly appear on the etched surface when using the H ₃PO ₄ or KOH solutions, respectively. A low concentration of H ₃PO ₄ (H ₃PO ₄: deionized water = 1:32, 1:64) produced a roughened surface with coexistence of dodecagonal and hexagonal pyramids. The photoluminescence (PL) intensity of the etched surfaces significantly increased due to multiple scattering events compared to the non-etched surface. Thus, the etching techniques developed in this study were shown to improve the light extraction efficiency of light emitting diodes (LEDs), avoiding the damage to the GaN typically created by plasma etching methods.