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This dissertation, Heteroepitaxial Growth of InN and InGaN Alloys on GaN(0001) by Molecular Beam Epitaxy by Ying, Liu, 劉穎, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled HETEROEPITAXIAL GROWTH OF InN AND InGaN ALLOYS ON GaN(0001) BY MOLECULAR BEAM EPITAXY Submitted by Liu Ying for the degree of Doctor of Philosophy at The University of Hong Kong in September 2005 Indium nitride (InN) and indium-gallium nitride (InGaN) alloys have attracted intensive interests recently due to their potentials in microelectronic and optoelectronic applications. Due to the lack of sizable InN or InGaN wafers, growths of such materials are carried out heteroepitaxially on some foreign substrates. Lattice mismatch strain between the epilayers and the substrates causes the Stranski-Krastanov (SK) growth mode, where three-dimensional (3D) islands form spontaneously. They may be incorporated in devices as the quantum dots (QDs) giving rise to better performances of the devices. To better utilize the QDs, it is necessary to know the properties of the 3D islands. In this thesis, heteroepitaxial growths of InN and InGaN on GaN(0001) by molecular-beam epitaxy (MBE) were investigated under various conditions. Using the excess indium (In) fluxes, the 3D InN islands nucleate via the conventional 2D-3D transitional mode and the islands are of pure InN, taking the equilibrium pillar-like shape. Under the excess nitrogen (N) fluxes, however, the 3D islands evolve from the coalescence of material cells on surface and the island shape changes from trapezoid to pyramid as the growth continues. The pyramidal islands appear to be kinetically limited and the constituent material is InGaN alloy rather than binary InN caused by a mass transfer from the wetting layer and the GaN buffer to the islands. Despite the differences between islands grown under different conditions, the sizes of the islands show the scaling property, indicating the insignificant role played by strain in island nucleation and coarsening processes. Using Patterson function (PF) inversion of low-energy electron diffraction (LEED) I-V curves, the atomic structure of InN wetting layer was revealed. Instead of the equilibrium wurtzite structure, the metastable cubic phase of the wetting layer was noted. An incommensurate surface structure was also discovered, which was found to originate from surface excess metal layers. Annealing such a surface induces the ( 3 3 )R30 surface reconstruction and the atomic origin of it can be attributed to be the replacement of surface In atoms by Ga, where the Ga coverage amounts to 2/3 layers. Finally, for the growth of InGaN alloys, film growth mode and its dependence on alloy composition, the effect of In atom surface segregation were all followed. The incorporation coefficients of Ga and In were derived. During the alloy growth, incorporation of Ga was found to be more efficient than that of In. Over a certain range of surface coverage, both coherent and dislocated islands were found to exist on surface. The coherent islands are cone-shaped and small, whereas the dislocated ones are pillar- like and generally larger. As the deposition proceeds, the coherent islands grow very little whereas the dislocated islands enlarge significantly, leading to an overall bimodal island size distribution. DOI: 10.5353/th_b3636355 Subjects: Crystal growthIndium alloysGallium compoundsMolecular beam epitaxy

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