Comparative discrimination methods were used to identify various line and planar defects observed in non-polar a-GaN epilayers on r-sapphire substrates. Unlike the case of conventional c-GaN, which was dominated by perfect threading dislocations, systematic identification of undistinguishable defects using transmission electron microscopy was necessary to suppress the propagation of defects in non-polar GaN epilayers. Cross-sectional transmission electron microscopic images near the [00•1] zone axis revealed that perfect mixed and pure screw type dislocations were visible, while pure edge and basal stacking faults were not discernible. In tilted cross-sectional transmission electron microscopic images along the [1¯2•0] zone axis, the dominant defects were basal stacking faults and partial dislocations for the g = ¯10•0 and 00•2 two-beam images, respectively. From plan-view transmission electron microscopic images taken along the [11•0] axis, it was found that the dominant partial and perfect dislocations were Frank-Shockley and mixed dislocations, respectively. Prismatic stacking faults were observed as inclined line contrast near the [00•1] zone axis and were visible as band contrast in the two-beam images along the [1¯2•0]  and [11•0] zone axes.

Classification of Stacking Faults and Dislocations Observed in Nonpolar a-Plane GaN Epilayers using Transmission Electron Microscopy. B.H.Kong, Q.Sun, J.Han, I.H.Lee, H.K.Cho: Applied Surface Science, 2012, 258[7], 2522-8