X-ray photoelectron diffraction from cubic GaN(001): an experimental and theoretical study

We have measured the polar scans from a cubic GaN(001) single crystal by X- ray photoelectron diffraction (XPD) with high angular resolution. The inten sities were recorded within (100), (110) and (110) substrate planes from Mg K alpha excited N 1s and Ga 3d core levels. The data reveal unexpected sha pes in forward focusing peaks for the N Is XPD patterns. Along [001] and [1 11] directions a large splitting in the structures is observed. The observe d patterns are reproduced very well by a multiple scattering spherical wave cluster calculation but the single scattering approach is sufficient to qu alitatively explain the remarkable features in the N Is profiles. In partic ular we demonstrate that the splitting of the structures along some low ind ex crystallographic directions is caused by the predominance of interferenc e phenomena due to atoms located in specific positions close to the dense a tomic chains. As a result of the smaller forward scattering amplitude of th e N atoms as compared to that of the Ga atoms, the interference effects are strongly reinforced when there are Ga atoms close to N atomic chains. In t he Ga 3d XPD patterns these interference effects also appear but forward sc attering still prevails along low index directions. (C) 2001 Elsevier Scien ce B.V. All rights reserved.