Epitaxial thin films are widely studied in the interest of fundamental scientific research into the physical properties of materials, but also due to the emerging demands of high efficiency in a wide range of industrial applications.
Among the most famous epitaxial thin films are GaN films for LED applications, the development of which led to the awarding of the Nobel Prize in Physics in 2014. The GaN heteroepitaxial films for these LEDs were grown on sapphire substrates after overcoming the large lattice mismatch between them. Though a symmetric similarity for c-axis growth of GaN (hexagonal) on the c-plane of sapphire (trigonal) exists, these two materials are totally different in the crystallographical sense. Complex domain structures and large mosaic spread (tilt/twist) of GaN epitaxial films were caused mainly by the large lattice mismatches.
In the pursuit of new characteristics comparable to GaN-LEDs, recent studies have concentrated on growing functional thin films epitaxially crystallographically different substrates. In this process, XRD analysis will be very helpful to characterize their orientation relationships, crystalline quality, etc.