Determination of Band-Gap Bowing for Al_xGa_(1-x)N Alloys

摘要

Contrary to the well established band gap of GaN, widely varying values are reported for Al_xGa_(1-x)N thin layers. The large difference is related to different growth techniques, conditions, and misinterpretation of the measured values. A solution of this problem is presented. Al_xGa_(1-x)N epitaxial thin films were grown on sapphire by MOCVD, and the absolute dependence of the band gap on Al content was found, independent of growth conditions. The large biaxial strain in Al_xGa_(1-x)N epitaxial thin films must be considered when extracting the Al content from X-ray diffraction (XRD). The XRD thickness correction procedure is a mathematical function, which can be used to calibrate the measured lattice parameter to the value of an unstrained layer, for each given layer thickness. The result was compared to the EDS analysis, with an excellent match. The energy gap was measured in transmission experiments, giving a downward bowing parameter of 1.38 eV.