TEM structural studies of undoped and Si-doped GaN grown on Al2O3 substrate

Transmission electron microscopy was used to study the microstructure of GaN films undoped or Si-doped to 10¹⁷ or 10¹⁸ cm^?3 and grown by molecular-beam epitaxy on (0001) Al₂O₃ substrate without nitridation or a buffer layer. Defect structures including inversion domains, nanopipes, and (0001) stacking faults were studied. The influence of Si doping on the threading dislocation density and the dimensions of GaN grains bounded by inversion domains was assessed. Smoothing of the steplike morphology of the GaN film surface occurs at a Si concentration of 10¹⁷ cm^?3.