X-ray photoelectron diffraction from cubic GaN(0 0 1): an experimental and theoretical study

We have measured the polar scans from a cubic GaN(0 0 1) single crystal by X-ray photoelectron diffraction (XPD) with high angular resolution. The intensities were recorded within (1 0 0), (1 1 0) and (1 1̄ 0) substrate planes from Mg Kα excited N 1s and Ga 3d core levels. The data reveal unexpected shapes in forward focusing peaks for the N 1s XPD patterns. Along [0 0 1] and [1 1 1] directions a large splitting in the structures is observed. The observed patterns are reproduced very well by a multiple scattering spherical wave cluster calculation but the single scattering approach is sufficient to qualitatively explain the remarkable features in the N 1s profiles. In particular we demonstrate that the splitting of the structures along some low index crystallographic directions is caused by the predominance of interference phenomena due to atoms located in specific positions close to the dense atomic chains. As a result of the smaller forward scattering amplitude of the 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 the Ga 3d XPD patterns these interference effects also appear but forward scattering still prevails along low index directions.