Germanium doping of GaN by metalorganic chemical vapor deposition for polarization screening applications

We demonstrate n-type doping of GaN with Ge by MOCVD at high concentrations that are necessary to fully screen the polarization fields in c-plane InGaN/GaN quantum wells. Hall measurements show linear Ge incorporation with dopant flow rate and carrier concentrations exceeding 1x10(20) cm(-3). GaN:Ge layers exhibit excellent electron mobility, high conductivity, and contact resistivity comparable to the best unannealed contacts to Si-doped GaN. However, the surface morphology begins to degrade with Ge concentrations above 1 x 10(19) cm(-3), resulting in severe step bunching and a network of plateaus and trenches, even in layers as thin as 10 nm.