This book provides an introduction to the X-ray diffraction analysis of key structural parameters in epitaxial GaN layers. Fundamental crystallographic concepts are introduced and related to the specific requirements of the technological structures created for optoelectronic and electronic devices employing GaN and related compounds.
The book is written for those who wish to gain a deeper appreciation of the principles behind XRD applications in the ever advancing field of compound semiconductor devices. It is also written for those who are engaged in the measurement of epitaxial layers who are looking for a background explanation of the concepts employed in proprietary analysis software such as Epitaxy, and those looking for a pathway through the analysis process so that they can design their own calculations. Whilst the solutions and the examples presented here are focused on GaN technology, the principles are generally transferable to solutions for other compound semiconductor systems.
Chapter 1 introduces, very briefly, concepts in GaN device technology that are relevant to XRD metrology.
Chapter 2 provides the background to expressions of crystal structure, crystal dimensions and crystal orientation, and procedures for calculating strain, composition and layer thickness in epitaxial thin films.
Chapter 3 introduces the principles of experiments used to obtain diffraction peak positions and the application of Bragg’s law to obtain crystallographic d-spacings.
Chapter 4 introduces the methods of diffraction pattern simulation and fitting as an alternative route to obtaining epitaxial layer thicknesses, compositions and strains.
Chapter 5 describes in principle how measurements of peak widths can be used to give some guide to mosaic block sizes and tilts and hence dislocation densities in GaN buffer layers.