Figure 2

X-ray diffraction measurements of GaN wires grown on Si (111) with an intermediate AlN layer. (a) Symmetric Θ-2Θ scan performed on a laboratory setup (approximately 0.179 nm Co-wavelength) and indexed with Si, GaN and AlN Bragg K_α1 reflections. Dots and squares correspond respectively to the K_α2 and K_β excitation wavelengths. The broad and low intensity peak around 51° (see the triangle) is attributed to a diffraction tail of the Si substrate. (b) Rocking curves (Δω-scan) of the GaN (0002) and (0004) peaks. (c,d) Grazing incidence X-ray diffraction performed at ESRF along the $\left[22\stackrel{͞}{4}\right]$ silicon direction (approximately 0.1203 nm wavelength and 0.18° incidence).