Wet-Chemical Etching of GaN: Underlying Mechanism of a Key Step in Blue and White LED Production

Gallium nitride (GaN) is the key material for the fabrication of blue and white light emitting diodes (LEDs). Etching of this material is applied to improve the light extraction efficiency of the product. Wet-chemical etching of GaN is commonly carried out by treatment with aqueous KOH solution at elevated temperature. Thereby, the anisotropic etching results in a highly rough surface. Hence, a remarkably higher out-coupling possibility of generated photons is feasible. On the other hand, anisotropy generally prohibits the application of a predictable and standardized etching process. In this review, both material- and process-dependent influences on the etching performance in aqueous KOH solution are classified. Herein, we critically present the factors that affect the etching rate of GaN. Moreover, the etching mechanism at the molecular level and the generation of anisotropy from the hexagonal crystal lattice are discussed. The existing gaps in the current understanding of this process maintain the field still open for further research aligned to a permanent interest of the electronic industry.