X-ray diffraction solutions to heteroepitaxial growth problems

Abstract

Modern X-ray diffraction equipment offers a wide choice of methods for understanding the problems involved in the heteroepitaxial growth of a wide range of materials. The basic double axis rocking curve continues to play a key role in the characterisation of heteroepitaxial strained layer structures. The strength of the technique arises from the ability to accurately simulate the diffraction process using the Takagi-Taupin formulation of dynamic theory. There is an increasing use of diffraction space mapping for the less perfect heteroepitaxial systems with large lattice mismatches and different crystal structures, e.g. superconductors, gallium nitride on sapphire. Detailed studies of the state of relaxation of pseudomorphic systems can be achieved using the triple crystal diffractometer. The triple axis diffractometer can also be used to measure the unit cell distortion in good quality non-pseudomorphic systems. Where layers are less perfect and where layers are very thin lower resolution diffraction space mapping can provide useful information with a large reduction in data collection time.