We report here the characteristics of photoelectrochemical (PEC) etching of epitaxial InGaN
semiconductor thin films using a narrowband laser with a linewidth less than 1 nm. In the initial
stages of PEC etching, when the thin film is flat, characteristic voltammogram shapes are observed. Atlow
photo-excitation rates, voltammograms are S-shaped, indicating the onset of a voltage-independent ratelimiting
process associated with electron-hole-pair creation and/or annihilation. At high photoexcitation
rates, voltammograms are superlinear in shape, indicating, for the voltage ranges studied here,
a voltage-dependent rate-limiting process associated with surface electrochemical oxidation. As PEC
etching proceeds, the thin film becomes rough at the nanoscale, and ultimately the self-limiting etch
kinetics lead to an ensemble of nanoparticles. This change in InGaN film volume and morphology leads to
a characteristic dependence of PEC etch rate on time: an incubation time, followed by a rise, then a peak,
then a slow decay.
ã