Crystallographic wet chemical etching of p-type GaN

We demonstrate crystallographic wet chemical etching of p-type GaN with etch rates as high as 1.2 μm/min. Etchants used include molten KOH, KOH dissolved in ethylene glycol, aqueous tetraethylammonium hydroxide, and phosphoric acid (H₃PO₄), at temperatures ranging from 90 to 260°C. The observed crystallographic p-GaN etch planes are (0001), {101̄0}, and {101̄2}. The etch rates follow an Arrhenius characteristic with activation energies varying from 21 kcal/mol for KOH-based solutions to 33 kcal/mol for H₃PO₄. The etch rate and crystallographic nature for the various etching solutions are independent of conductivity, as shown by seamless etching of a p-GaN/undoped, high-resistivity GaN homojunction and by comparison of the etch rates of p-GaN with n-GaN.