Porous GaN: Anion-Specific Electrochemical Etching Mechanisms and Morphological Control.

Porous GaN has emerged as a promising material for enhancing the performance of optoelectronic devices and broadening the range of possible GaN applications. However, the electrochemical etching (ECE) process used to create porosity remains poorly understood, particularly regarding the impact of the chemical environment on pore morphology. Here, the controlled ECE of n-type GaN is systematically investigated across a range of etchant chemicals and pH values. It is shown that the identity, speciation, and relative concentrations of anionic species play dominant roles in dictating porous morphology. Through deliberate manipulation of anion compositions within an etchant solution, for example, by adjusting initial polyprotic acid concentration and/or addition of a conjugate salt, porous morphology and surface structure can be controlled and tuned effectively. Further, ECE-generated current oscillations, previously interpreted as evidence for an oxidation-dissolution ECE mechanism, are shown to correlate with the presence of dynamic anion equilibria, providing an additional mechanistic interpretation of n-type GaN ECE. This furthered understanding enables more tailored and application-specific control over porous structure, offering opportunities for optimized, bespoke GaN-based porous architectures.