title: Self-assembled Multilayers of Silica Nanospheres for Defect Reduction in Non- and Semipolar Gallium Nitride Epitaxial Layers.
abstract: Non- and semipolar GaN have great potential to improve the efficiency of light emitting devices due to much reduced internal electric fields. However, heteroepitaxial GaN growth in these crystal orientations suffers from very high dislocation and stacking faults densities. Here, we report a facile method to obtain low defect density non- and semipolar heteroepitaxial GaN via selective area epitaxy using self-assembled multilayers of silica nanospheres (MSN). Nonpolar (11-20) and semipolar (11-22) GaN layers with high crystal quality have been achieved by epitaxial integration of the MSN and a simple one-step overgrowth process, by which both dislocation and basal plane stacking fault densities can be significantly reduced. The underlying defect reduction mechanisms include epitaxial growth through the MSN covered template, island nucleation via nanogaps in the MSN, and lateral overgrowth and coalescence above the MSN. InGaN/GaN multiple quantum wells structures grown on a nonpolar GaN/MSN template show more than 30-fold increase in the luminescence intensity compared to a control sample without the MSN. This self-assembled MSN technique provides a new platform for epitaxial growth of nitride semiconductors and offers unique opportunities for improving the material quality of GaN grown on other orientations and foreign substrates or heteroepitaxial growth of other lattice-mismatched materials.
authors.affiliation: Department of Materials Science and Metallurgy, University of Cambridge , 27 Charles Babbage Road, Cambridge CB3 0FS, United Kingdom.
authors.forename: Tongtong
authors.initials: T
authors.lastname: Zhu
authors.affiliation: Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, United Kingdom; Nanophotonics Centre, Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, United Kingdom.
authors.forename: Tao
authors.initials: T
authors.lastname: Ding
authors.affiliation: Department of Materials Science and Metallurgy, University of Cambridge , 27 Charles Babbage Road, Cambridge CB3 0FS, United Kingdom.
authors.forename: Fengzai
authors.initials: F
authors.lastname: Tang
authors.affiliation: Department of Materials Science and Metallurgy, University of Cambridge , 27 Charles Babbage Road, Cambridge CB3 0FS, United Kingdom.
authors.forename: Yisong
authors.initials: Y
authors.lastname: Han
authors.affiliation: Cambridge Research Laboratory, Toshiba Research Europe Limited , 208 Science Park, Milton Road, Cambridge CB4 0GZ, United Kingdom.
authors.forename: Muhammad
authors.initials: M
authors.lastname: Ali
authors.affiliation: Cambridge Research Laboratory, Toshiba Research Europe Limited , 208 Science Park, Milton Road, Cambridge CB4 0GZ, United Kingdom.
authors.forename: Tom
authors.initials: T
authors.lastname: Badcock
authors.affiliation: Department of Materials Science and Metallurgy, University of Cambridge , 27 Charles Babbage Road, Cambridge CB3 0FS, United Kingdom.
authors.forename: Menno J
authors.initials: MJ
authors.lastname: Kappers
authors.affiliation: Cambridge Research Laboratory, Toshiba Research Europe Limited , 208 Science Park, Milton Road, Cambridge CB4 0GZ, United Kingdom.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Shields
authors.affiliation: Department of Materials Science and Metallurgy, University of Cambridge , 27 Charles Babbage Road, Cambridge CB3 0FS, United Kingdom.
authors.forename: Stoyan K
authors.initials: SK
authors.lastname: Smoukov
authors.affiliation: Department of Materials Science and Metallurgy, University of Cambridge , 27 Charles Babbage Road, Cambridge CB3 0FS, United Kingdom.
authors.forename: Rachel A
authors.initials: RA
authors.lastname: Oliver