Depth-dependent tetragonal distortion study of AlGaN epilayer thin film using rbs and channeling technique

摘要

An epilayer of wide-band gap Al _xGa _(1-x)N was grown on sapphire by metal organic chemical vapor deposition (MOCVD) method with a GaN buffer layer of thickness slightly greater than 1 μ m. Average composition of Al in the AlGaN layer is determined by Rutherford backscattering spectroscopy (RBS). Simulation of the random spectra reveals that the AlGaN layer has a composition of Al0.05Ga0.95N and a thickness of 200 nm. Low ratio of channeling and random spectra yields suggests good crystalline quality of ternary AlGaN epilayer. Tetragonal distortion (eT) caused by elastic strain in AlGaN is measured from channeling angular scans taken around an off-normal 12?13 axis in the {101?0} plane of the AlGaN layer. The resulting AlGaN is identified to be showing compressive strain at the interfacial layer and the magnitude of the stress reduces towards the near-surface layer. It can be expected from the results that a 550 nm thick, epitaxially grown, AlGaN layer on sapphire can be relaxed completely (eT = 0).