Simulating Patterns of Non-centrosymmetric Crystals: GaP

In some crystals the “front” side and “back” side of certain lattice planes are different, a polar effect which can only be reproduced using dynamical simulations. Some of these materials are very important in the semiconductor industry (e.g., GaN, Al(x)Ga(1-x)As, GaP and InP) where the control of film polarity can be of great interest. Using dynamical theory, the correct orientation is found to have a higher correlation coefficient r with respect to the experimental pattern, compare how the Kikuchi band intensities shift more towards the outside or inside of the triangular Kikuchi band structure surrounding the three-fold zone axis in the upper middle of the pattern.

Gallium atoms (green) and phosphor atoms (red) in the unit cell models have exchanged positions in the two orientations shown below. Except for this exchange of both atomic species in the crystal, the orientations are otherwise exactly similar and cannot be distinguished by the standard kinematical simulation models.