Surface Images of GaN

The first image is an optical micrograph, the next 4 are AFM Images. All images are from the same (0001) oriented, OMVPE grown GaN film

For more details about these results, see:
W. Qian, G. S. Rohrer, M. Skowronski, K. Doverspike, L. B. Rowland, and D. K. Gaskill, "Open-Core Dislocations in GaN Epilayers Observed by SFM and High Resolution TEM", Applied Physics Letters 67 (1995) 2284.
or
G. S. Rohrer, J. Payne, W. Qian, M. Skowronski, K. Doverspike, L. B. Rowland, and D. K. Gaskill, "A Microscopic Evaluation of the Surface Structure of OMVPE Deposited a-GaN Epilayers" in GaN and Related Materials edited by F.A. Ponce, R.D. Dupuis, S. Nakamura, and J.A. Edmond (Mater. Res. Soc. Proc. 395, Pittsburgh, PA, 1996), p. 381.