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18 August 2009 III-nitride epilayers on ZnO substrates by MOCVD using Al2O3 as a transition layer
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ZnO is a promising substrate for GaN growth due to a lattice match with In.18Ga.82N, similar thermal expansion coefficient, and its ability to be easily chemically etched, which results in improved light extraction. A transition layer of Al2O3 was also grown by ALD prior to MOCVD growth to prevent Zn diffusion, protect the ZnO substrate from H2 back etching, and promote high quality nitride growth. Thick InGaN layers (~200-300nm) were grown in this study on bare ZnO substrates and ALD/ZnO substrates. Various buffer layers were attempted, such as SLs of AlGaN/GaN, MQWs of InGaN/GaN, and LT-GaN. These results are significant as previous studies showed decomposition of the layer at InGaN thicknesses of 100nm or less. These layers allowed for the first LEDs to be grown on bare ZnO substrates. This study demonstrated that InGaN LEDs showed emission in optical measurements as well as a high IQE of ~60%. The data shows promise for LED structures on ZnO using InGaN as n- and p-type LED layers. Etching of the ZnO substrate also showed that removal of the substrate can be performed easily.
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Nola Li, Will Fenwick, Andrew Melton, I-Hsiang Hung, Zhe Chuan Feng, Christopher Summers, Muhammad Jamil, and Ian Ferguson "III-nitride epilayers on ZnO substrates by MOCVD using Al2O3 as a transition layer", Proc. SPIE 7422, Ninth International Conference on Solid State Lighting, 74220J (18 August 2009);

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