Structural characterization of AlGaN/GaN superlattices by three-beam X-ray diffraction

Three-beam X-ray diffraction in AlGaN/GaN superlattices (SLs) grown by metalorganic chemical vapor deposition on $c$-sapphire has been measured in the Renninger scheme. The primary beam corresponds to a forbidden 0001 reflection. Then, $\theta$-scan curves were measured at the maximum of each three-beam diffraction peak. The average parameters $a$ and $c$ of SLs have been determined using the angular positions of three-beam diffraction peaks on the Renninger diagram ($\varphi$-scan curves). It is shown that a diffraction pattern with satellites on the $\theta$–2$\theta$ curve of 0001 reflection can be obtained in the azimuthal position of three-beam diffraction. The angular widths of three-beam diffraction peaks measured in both $\varphi$ and $\theta$ scans have been analyzed as related to the defect structure of layers. On this basis, a new method of determining the structural parameters of SLs is proposed.