Silicon implantation in epitaxial GaN layers: Encapsulant annealing and electrical properties

Silicon ions have been implanted into GaN layers epitaxially grown on an AlN/(0001)-Al2O3 substrate to a dose of 1×1015/cm2. The Si-implanted GaN has been rapid thermal annealed at temperatures between 800 and 1250 °C. Thermal pits are formed in the surface during annealing at 1200 °C, resulting in deterioration of the morphology. The surface deterioration is effectively suppressed by using a 140-nm-thick Si3N4 film as an encapsulant during annealing up to 1250 °C. The electrical activation process for Si atoms has an activation energy of 3.1 eV in the range of 1000 to 1250 °C. Carrier concentration and mobility profiles for n-type layers formed by Si implantation have been examined by differential Hall-effect measurements. A very high electrical activity for implanted Si atoms of 86% can be achieved, and a highly doped n-type layer with a peak carrier concentration of 6×1019/cm3 is formed after annealing at 1250 °C. Electrons generated from Si atoms located near the end of range are trapped by defects remaining after annealing at 1250 °C.