Currently, in the electronics business, gallium nitride, GaN, and related compounds are fast becoming major players. This book aims to provide an overview of the X-ray diffraction analysis of key structural parameters in epitaxial GaN layers. It introduces fundamental crystallographic concepts and how these relate to the specific requirements of the technological structures created for optoelectronic and electronic devices.
It is aimed at those wishing to gain a deeper understanding of the principles behind XRD applications in the continually advancing compound semiconductor devices field. It also provides a background explanation of the concepts employed in proprietary analysis software such as X’Pert Epitaxy for those who are engaged in the measurement of epitaxial layers and for those who would like to understand the analysis process to enable them to design their calculations. This book focuses on GaN technology, but the principles are mostly transferable to solutions for other compound semiconductor systems.
High-resolution rocking curves and reciprocal space maps are primarily used in the discussion of solution in this book. While other methods are available to investigate advanced materials, these are the most common applications in GaN device technology. Research environments often use reflectometry, in-plane scattering, SAXS and GISAXS as X-ray diffraction methods.
Rapid measurement and automation are continually improving through the emergence of new methods. A separate publication will detail these experimental methods. Malvern Panalytical X’Pert MRD and X’Pert MRD XL equipment can be used to carry out all of the measurements referred to in this book.
Precise and quantitative measurements are described using epitaxial device structures. The relative quality of defective epitaxial layers can be measured through several alternative methods. Such approaches include peak shape and width measurements (and via this route an exploration of mosaic block sizes), crystallographic tilts and rotations and estimations of defect densities and textural spread. Also introduced are the principles involved in qualitative analyses.
- Chapter 1 provides a brief introduction to GaN device technology concepts relevant to XRD metrology.
- Chapter 2 discusses expressions of crystal structure, crystal dimensions and crystal orientation, as well as procedures for calculating strain, composition and layer thickness in epitaxial thin films.
- Chapter 3 provides an introduction for obtaining diffraction peak positions and the application of Bragg’s law to obtain crystallographic d-spacings.
- Chapter 4 provides an introduction to an alternative route to obtaining epitaxial layer thicknesses, compositions and strains in terms of the methods of diffraction pattern simulation and fitting.
- Chapter 5 discusses how to use measurements of peak widths as a guide to mosaic block sizes and tilts and hence dislocation densities in GaN buffer layers.
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