Quantitative electron microscopy of InN-GaN alloys

Time series of high-resolution lattice images are examined to probe for possible alterations of the indium distribution in GaN/InxGa1-xN/GaN quantum well structures during electron irradiation with energies of 150 kV and 800 kV. By comparison with theory it is reasoned that sample preparation, microscope stability, and chosen acceleration voltages are essential factors that determine the reliability of the results. If considered, it is shown that for relevant time scales of <2 minutes and current densities of 20-40 A/cm2 no measurable alteration of the initial element distribution occurs. A quantitative method is highlighted for the characterization of existing indium fluctuations that are concentration dependent. Consistency between measurements from lattice images, Z-contrast images, and local band gap measurements support our conclusion. It is argued that the formation of such indium clusters is driven by strain-dependent spinodal decomposition. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)