Scanning tunnelling microscopy images confirmed electron diffraction studies that the zincblende GaN(001)-4x reconstruction consisted of rows aligned along [¯110], with a spacing along [1¯10] of 4a. Dual-bias imaging showed a 180° shift of the corrugation maximum position between the profiles of empty and occupied states, in agreement with surface simulations based on the 4 x 1 linear tetramer model of Neugebauer et alia (1998). Electronic structure calculations predicted a surface band gap of 1.1eV, close to the measured value of 1.14eV and the previously predicted value (1.2eV). Despite the successes of this model, high-resolution images reveal an unexpected 3x periodicity (not seen in diffraction) along the [110] row direction, indicating the need for a 4 x 3 model, and putting into question the existence of linear Ga tetramers.

Scanning Tunnelling Microscopy and Surface Simulation of Zincblende GaN(001) Intrinsic 4x Reconstruction - Linear Gallium Tetramers? H.A.H.Al-Brithen, R.Yang, M.B.Haider, C.Constantin, E.Lu, A.R.Smith, N.Sandler, P.Ordejón: Physical Review Letters, 2005, 95[14], 146102 (4pp)