Shape transformation of nanoporous GaN by annealing: From buried cavities to nanomembranes

Gallium nitride is considered a chemically inert, ceramic-like semiconductor with no effective etchants available at room temperature. In this letter, we study the shape transformation of nanoporous GaN prepared by an electrochemical process. It is found that the curvature-driven mass transport process at typical growth temperatures is effective in shaping GaN on both the nanoscale and microscale into useful configurations such as buried cavities or semiconductor-on-air structures. This process of "micromachining" GaN adds flexibilities to epitaxy and device designs. A monocrystalline GaN nanomembrane, extending millimeters in width, is reported as a proof-of-concept demonstration.