X-ray photoelectron spectroscopy was used to study the chemical composition and electronic structure of the Y 3 Al 5 O 12 :Yb (YAG:Yb) crystals. The contamination of the crystal with carbon and oxygen in the broken under UHV sample was found. The dopant concentration of Yb, in the mixed valence state, was determined as 12 %. The aluminium concentration is lower than a nominal value. The chemical shift analysis shows more ionic bond of Y-O than Al-O.
The potential of the high-growth rate hydride vapour phase epitaxy technique and laser lift-off for the fabrication of free-standing GaN substrates is explored. Structural and optical properties of 300 µm thick free-standing GaN have been investigated employing different analytical techniques. The x-ray diffraction (XRD) measurements prove good crystalline quality of the material grown. A comparatively low value of (3 ± 1) × 1016 cm−3 of Ga vacancy-related defects is inferred from positron annihilation spectroscopy data. Complete strain relaxation is observed on the Ga-polar face of the free-standing GaN by XRD and Raman spectroscopy measurements. The strain-free homoepitaxy will significantly reduce the defect density, and thus an improvement of the device performance and lifetime can be realized.
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