Commercially, GaN crystals can be grown using molecular beam epitaxy or metalorganic vapour phase epitaxy. This process can be further modified to reduce dislocation densities.  First, an ion beam is applied to the growth surface in order to create nanoscale roughness.  Then, the surface is polished. This process takes place in a vacuum. Polishing methods typically employ a liquid electrolyte and UV irradiation to enable mechanical removal of a thin oxide layer from the wafer. More recent methods have been developed which utilize solid-state polymer electrolytes which are solvent-free and require no radiation before polishing.