ZnO homoepitaxy on the O polar face of hydrothermal and melt-grown substrates by pulsed laser deposition |
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Authors: | DJ Rogers F Hosseini Teherani A Largeteau G Demazeau C Moisson D Turover J Nause G Garry R Kling T Gruber A Waag F Jomard P Galtier A Lusson T Monteiro MJ Soares A Neves MC Carmo M Peres G Lerondel C Hubert |
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Institution: | (1) Nanovation SARL, 103bis, rue de Versailles, 91400 Orsay, France;(2) Technical University of Troyes-CNRS (FRE2671), 12 rue Marie Curie, BP 2060, 10010 Troyes, France;(3) ICMCB-CNRS, Bordeaux 1 University (Science & Technology), 87 Av. A. Schweitzer, 33608 Pessac, France;(4) Novasic, Savoie Technolac, Arche Bat. 4, BP 267, 73375 Le Bourget du Lac, France;(5) Cermet Inc., 1019 Collier Road, Atlanta, GA 30318, USA;(6) Domaine de Corbeville, Thales Research, 91401 Orsay, France;(7) Department of Semiconductor Physics, Ulm University, 89069 Ulm, Germany;(8) Institute of Semiconductor Technology, Braunschweig Technical University, 38106 Braunschweig, Germany;(9) LPSC-CNRS, 1 Place Aristide Briand, 92195 Meudon, France;(10) Physics Department, University of Aveiro, 3810-193 Aveiro, Portugal |
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Abstract: | 2 cm diameter hydrothermal ZnO crystals were grown and then made into substrates using both mechanical and chemical-mechanical polishing (CMP). CMP polishing showed superior results with an (0002) Ω scan full width half maximum (FWHM) of 67 arcsec and an root mean square (RMS) roughness of 2 Å. In comparison, commercial melt-grown substrates exhibited broader X-ray diffraction (XRD) linewidths with evidence of sub-surface crystal damage due to polishing, including a downward shift of c-lattice parameter. Secondary ion mass spectroscopy revealed strong Li, Fe, Co, Al and Si contamination in the hydrothermal crystals as opposed to the melt-grown substrates, for which glow discharge mass spectroscopy studies had reported high levels of Pb, Fe, Cd and Si. Low temperature photoluminescence (PL) studies indicated that the hydrothermal crystal had high defect and/or impurity concentrations compared with the melt-grown substrate. The dominant bound exciton for the melt-grown substrate was indexed to Al. ZnO films were grown using pulsed laser deposition. The melt-grown substrates gave superior results with XRD (0002) Ω and 2θ/Ω WHM of 124 and 34 arcsec, respectively. Atomic force microscope measurements indicated a low RMS roughness (1.9 nm) as confirmed by fringes in the XRD 2θ/Ω scan. It was suggested that the improvement in XRD response relative to the substrate might be due to “healing” of sub-surface polishing damage due to the elevated Ts used for the growth. Indeed the c-lattice parameter for the homoepitaxial layer on the melt-grown substrate had become that which would be expected for strain-free ZnO. Furthermore, the stability of the PL peak positions relative to bulk ZnO, confirmed that the films appear practically strain free. |
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