A scratch-free and atomically flat (00•1) surface of 6H-type SiC was prepared by using a 2-step method which combined atmospheric H-treatment with ultra-high vacuum Si etching. A high-quality GaN(00•1) thin film was deposited onto this surface by means of radio-frequency N plasma-assisted molecular beam epitaxy. Its surface exhibited a typical terrace-plus-step morphology, which permitted the study of various GaN(00•1) surface superstructures and hollow-core defects using scanning tunnelling microscopy. The hollow-core defects had diameters which were of the order of 40nm. In some cases, the hollow core was surrounded by 4 screw-dislocation bunching. The corresponding Burgers vector was directed along the [00•1] direction, and had a value of 2.08nm. The formation of the hollow-core dislocation could be explained by the Frank model. That is, when the magnitude of the Burgers vector of a dislocation exceeded a critical value, it was energetically more favorable to remove the highly strained region around the dislocation and to create an additional free surface in the shape of a tube.

Two-Step Preparation of 6H-SiC(0001) Surface for Epitaxial Growth of GaN Thin Film. Q.Xue, Q.K.Xue, Y.Hasegawa, I.S.T.Tsong, T.Sakurai: Applied Physics Letters, 1999, 74[17], 2468-70