Studies on Si-doped AlGaN Epilayers

Growth optimization of Si doped AlGaN epilayers—with 20%, 30% and 45%Al content— grown on AlGaN-sapphire by MOVPE was investigated. We could realize n-type carrier concentrations from about 2 × 10 cm to 1 × 10 cm. The layers with high levels of dopants suffer from crack formation. Therefore, we used a short period super lattice to manage the strain between the doped layer and the undoped buffer layer. The XRD investigations were performed to reveal the strain evolution in our layers with respect to the dopant concentration. Using variable temperature Hall measurements on such films, the activation energy of the Si-donors was evaluated. We found a fairly small activation energy confirming that the doping concentrations are in the range of the Mott transition.