Anisotropy and Mechanistic Elucidation of Wet-Chemical Gallium Nitride Etching at the Atomic Level
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Etching of gallium nitride is a key step in the production of blue and white light-emitting diodes (LEDs). Etching in aqueous KOH solution creates a rough surface on the LED chip to facilitate outcoupling of the photons generated, drastically increasing the resulting LED’s efficiency. Compared with the common technique of dry etching, wet-chemical etching using aqueous KOH solution has significant advantages, e.g., lower complexity and cost and less remaining surface damage. An in-depth analysis of the molecular etch reaction by characterization of the reaction products is reported. The mechanism identified explains the cause of anisotropic etching, which leads to the formation of hexagonal pyramids. The concept of hydroxide repulsion by protruding NH and NH2 groups established in the literature is adapted and further developed. The susceptibility of several polar, semipolar, and nonpolar crystal facets may also be explained, as well as the commonly observed increase in average pyramid size over etch time.