A Comparative Study of MBE‐Grown GaN Films Having Predominantly Ga‐ or N‐Polarity

Wurtzitic GaN epilayers having both Ga and N‐polarity were grown by reactive molecular beam epitaxy (MBE) using a plasma‐activated nitrogen source on c ‐plane sapphire. The polarities were verified by convergent beam electron diffraction (CBED). High‐resolution X‐ray diffraction, atomic force microscopy (AFM) imaging and transmission electron microscopy (TEM) were employed to characterize the structural defects present in the films. The different topographic features of Ga and N‐polarity samples and their appearance after wet etching were correlated to the measured X‐ray rocking curve peak widths for both symmetric [0002] and asymmetric [ $10\bar 14$ ] diffraction. For Ga‐polarity samples, the [0002] diffraction is narrower than the [ $10\bar 14$ ] diffraction, while for N‐polarity ones the [0002] peaks are broader than [ $10\bar 14$ ]. The half width of [ $10\bar 14$ ] peaks for both polarity types were in the range of 5–7 arcmin indicative of, among possibly other defects, a high density of pure edge threading dislocations lying parallel to the c ‐axis. The 1–2 arcmin [0002] linewidths of Ga‐polarity samples suggest a low density of screw dislocations, which corresponds with the TEM observations where the screw dislocation density is less than 10 7 cm —2 . In N‐polarity samples, however, the [0002] diffraction peak was typically wider than 5 arcmin, suggesting either a higher density of edge dislocations and inversion domains in N‐polarity samples, or the columnar structural features in AFM images, where the effective coherence length for X‐ray diffraction is drastically reduced.