Microstructure and strain analysis of GaN epitaxial films using in-plane grazing incidence x-ray diffraction

This paper investigates the major structural parameters, such as crystal quality and strain state of (001)-oriented GaN thin films grown on sapphire substrates by metalorganic chemical vapour deposition, using an in-plane grazing incidence x-ray diffraction technique. The results are analysed and compared with a complementary out-of-plane x-ray diffraction technique. The twist of the GaN mosaic structure is determined through the direct grazing incidence measurement of (100) reflection which agrees well with the result obtained by extrapolation method. The method for directly determining the in-plane lattice parameters of the GaN layers is also presented. Combined with the biaxial strain model, it derives the lattice parameters corresponding to fully relaxed GaN films. The GaN epilayers show an increasing residual compressive stress with increasing layer thickness when the two dimensional growth stage is established, reaching to a maximum level of -0.89 GPa.

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Project supported by the National Natural Science Foundation of China (Grant Nos. 60506001, 60776047, 60976045 and 60836003), the National Basic Research Programme of China (Grant No. 2007CB936700) and the National Science Foundation for Distinguished Young Scholars, China (Grant No. 60925017).

国内

Project supported by the National Natural Science Foundation of China (Grant Nos. 60506001, 60776047, 60976045 and 60836003), the National Basic Research Programme of China (Grant No. 2007CB936700) and the National Science Foundation for Distinguished Young Scholars, China (Grant No. 60925017).