Structural investigations were made, of organometallic vapor phase epitaxially grown -phase films, by using high-resolution transmission electron microscopy and scanning force microscopy. This revealed the presence of tunnel-like defects, with radii of 3.5 to 50nm, which were aligned along the growth direction of the crystal and penetrated through the entire epilayer. These so-called nanopipes terminated at the free surface of the films, at the centers of hexagonal growth hillocks, and formed craters with radii of 60 to 100nm. One or two pairs of monolayer-height spiral steps were observed to originate from the surface craters, and it was concluded that the nanopipes were the open cores of screw dislocations.

W.Qian, G.S.Rohrer, M.Skowronski, K.Doverspike, L.B.Rowland, D.K.Gaskill: Applied Physics Letters, 1995, 67[16], 2284-6