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Bias-dependent photoenhanced electrochemical etching of n-GaN using CH3COOH solution and KOH solution is described. During etching of n-GaN under an illumination of 90 mW/cm2, n-GaN was etched at a rate of 8 nm/min in 0.04 M of KOH solution, and negligible etching was shown in 1% CH3COOH solution at zero substrate bias. However, n-GaN was successfully etched by applying negative bias, and an etch rate of 286 nm/min resulted from the etching in 1% CH3COOH solution at a bias of -9 V and an illumination intensity of 125 mW/cm2. Etch rate increased with negative bias and illumination intensity for etching in both solutions.

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Etching characteristics for n-GaN on bias voltage were examined in various chemical solutions including the solutions not considered as etchants. n-GaN was not etched in HNO 3 and CH 3 COOH solutions during photo-enhanced electrochemical (PEC) etching under UV illumination of 90 mW/cm 2 . It was successfully etched in 1% CH 3 COOH solution by applying a bias larger than 0.6 V and the etch rate was increased to 23 nm/min at 1.5 V. Also, etching of n-GaN began to appear at 0.4 V in 0.05% HNO 3 solution. On the contrary, n-GaN was etched at a rate of 12 nm/ min in 0.04M KOH solution and 6 nm/min in 0.01M H 3 PO 4 solution even though the bias was not applied and --0.4 and --0.3 V were needed to stop the etching of n-GaN, respectively. The increase of etch rate on the reverse bias was shown for all the examined solutions and the critical bias for n-GaN etching was not varied on the UV illumination intensity.