Wednesday, February 25, 2009

X-Ray Diffraction of III-Nitrides

This is a terrific review of not only the x-ray diffraction of III-nitrides, but also a lesson in x-ray diffraction in general[1].

Abstract: The III-nitrides include the semiconductors AlN, GaN and InN, which have band gaps spanning the entire UV and visible ranges. Thin films of III-nitrides are used to make UV, violet, blue and green light-emitting diodes and lasers, as well as solar cells, high-electron mobility transistors (HEMTs) and other devices. However, the film growth process gives rise to unusually high strain and high defect densities, which can affect the device performance. X-ray diffraction is a popular, non-destructive technique used to characterize films and device structures, allowing improvements in device efficiencies to be made. It provides information on crystalline lattice parameters (from which strain and composition are determined), misorientation (from which defect types and densities may be deduced), crystallite size and microstrain, wafer bowing, residual stress, alloy ordering, phase separation (if present) along with film thicknesses and superlattice (quantum well) thicknesses, compositions and non-uniformities. These topics are reviewed, along with the basic principles of x-ray diffraction of thin films and areas of special current interest, such as analysis of non-polar, semipolar and cubic III-nitrides. A summary of useful values needed in calculations, including elastic constants and lattice parameters, is also given. Such topics are also likely to be relevant to other highly lattice-mismatched wurtzite-structure materials such as heteroepitaxial ZnO and ZnSe.

It is also a good introduction to the various level of complexities and capabilities of x-ray diffraction. One can get a good understanding of what the fuss is all about when a new synchrotron center opens, and why having a light source like that that produces such quality of x-rays (and other range of light) is so important.


[1] M.A. Moram and M.E. Vickers, Rep. Prog. Phys. v.72 p.036502 (2009).

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