X-ray diffraction investigation of GaN layers on Si(111) and Al2O3(0001) substrates - N. V. Safriuk; G. V. Stanchu; A. V. Kuchuk; V. P. Kladko; A. E. Belyaev; V. F. Machulin (Semiconductor Physics, Quantum Electronics and Optoelectronics, 2013)