Nanopipes in GaN: photo-etching and TEM study S. Lazar, J L Weyher, L. Macht, F. D. Tichelaar and H. W. Zandbergen Eur. Phys. J. Appl. Phys., 27 1-3 (2004) 275-278 Published online: 15 July 2004 DOI: 10.1051/epjap:2004047