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 (phi-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 phi 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.