@article{shelton_sachet_paisley_hoffmann_rajan_collazo_sitar_maria_2014, title={Polarity characterization by anomalous x-ray dispersion of ZnO films and GaN lateral polar structures}, volume={115}, ISSN={["1089-7550"]}, DOI={10.1063/1.4863120}, abstractNote={We demonstrate the use of anomalous x-ray scattering of constituent cations at their absorption edge, in a conventional Bragg-Brentano diffractometer, to measure absolutely and quantitatively the polar orientation and polarity fraction of unipolar and mixed polar wurtzitic crystals. In one set of experiments, the gradual transition between c+ and c− polarity of epitaxial ZnO films on sapphire as a function of MgO buffer layer thickness is monitored quantitatively, while in a second experiment, we map the polarity of a lateral polar homojunction in GaN. The dispersion measurements are compared with piezoforce microscopy images, and we demonstrate how x-ray dispersion and scanning probe methods can provide complementary information that can discriminate between polarity fractions at a material surface and polarity fractions averaged over the film bulk.}, number={4}, journal={JOURNAL OF APPLIED PHYSICS}, author={Shelton, Christopher T. and Sachet, Edward and Paisley, Elizabeth A. and Hoffmann, Marc P. and Rajan, Joseph and Collazo, Ramon and Sitar, Zlatko and Maria, Jon-Paul}, year={2014}, month={Jan} }
 @article{hussey_mita_xie_guo_akouala_rajan_bryan_collazo_sitar_2012, title={Lateral epitaxial overgrowth of nitrogen polar GaN on smooth nitrogen polar GaN templates by metalorganic chemical vapor deposition}, volume={112}, ISSN={["1089-7550"]}, DOI={10.1063/1.4768526}, abstractNote={Nitrogen (N)-polar GaN lateral epitaxial overgrowth (LEO), with a reduced dislocation density, is grown by metalorganic chemical vapor deposition on patterned, smooth N-polar templates. For LEO growth conditions identical to that of smooth N-polar GaN on sapphire, mask orientation dependent morphologies and faceting of the overgrowth regions are observed. N-polar LEO oriented along the 〈1-100〉 direction exhibit flat sidewall morphologies while LEO oriented along the 〈11-20〉 direction exhibit inclined sidewalls. A lateral to vertical growth ratio for the 〈1-100〉 and 〈11-20〉 oriented LEO was found to be ∼0.3 and 0.2, respectively. Transmission electron microscope observations reveal a reduction of dislocations of up to three orders of magnitude in the overgrowth regions from ∼1010 cm−2 in the template. Additionally, dislocation bending likely initiated from interfacial tension between the N-polar GaN and SiO2 mask is observed, resulting in a reduction of dislocation density to ∼109 cm−2 in the window region...}, number={11}, journal={JOURNAL OF APPLIED PHYSICS}, author={Hussey, Lindsay and Mita, Seiji and Xie, Jinqiao and Guo, Wei and Akouala, Christer-Rajiv and Rajan, Joseph and Bryan, Isaac and Collazo, Ramon and Sitar, Zlatko}, year={2012}, month={Dec} }