Microstructure of M-plane GaN epilayers grown on γ-LiAlO2 by plasma-assisted molecular beam epitaxy

We report on the defect structure of M-plane GaN(1(1) over bar $ 00) epilayers grown on gamma-LiAlO2(100) substrates by plasma-assisted molecular beam epitaxy. Our transmission electron microscopy studies reveal that the M-plane layers mainly contain intrinsic and extrinsic basal plane stacking faults. Beyond this, a complex type of planar defect is detected in the (10(1) over bar $0) prism plane which is inclined with respect to the interface. This prism plane boundary is connected to stacking faults intersecting the whole sample. Its displacement vector is along the c axis and thus not able to relieve the epitaxial strain. Threading dislocations are dissociated into Shockley partials. The origin of the defect microstructure is discussed with respect to the misfit strain and the substrate surface morphology.