Scanning tunneling microscopy and surface simulation of zinc-blende GaN(001) intrinsic 4× reconstruction: Linear gallium tetramers?

Scanning tunneling microscopy images confirm electron difraction studies that the zinc-blende GaN(001)-4× reconstruction consists of rows aligned along [110] with a spacing along [11̄0] of 4a. Dual-bias imaging shows a 180° shift of the corrugation maximum position between the profiles of empty and occupied states, in agreement with surface simulations based on the 4×1 linear tetramer model of Neugebauer et al. [Phys. Rev. Lett. 80, 3097 (1998)PRLTAO0031-900710.1103/PhysRevLett.80.3097]. Electronic structure calculations predict a surface band gap of 1.1 eV, close to the measured value of 1.14 eV and the previously predicted value (1.2 eV). Despite the successes of this model, high-resolution images reveal an unexpected 3× periodicity (not seen in diffraction) along the [110] row direction, indicating the need for a 4×3 model, and putting into question the existence of linear Ga tetramers.