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A High Temperature Hydride Vapor Phase Epitaxy reactor (HT-HVPE) was used to grow 5 µm-thick (0001) epitaxial AlN layers on sapphire. The experimental set-up consists of a vertical cold-wall quartz reactor working at low pressure in which the reactions take place on a graphite susceptor heated by induction. The reactants used are ammonia (NH3) and aluminum chlorides (AlClx) in situ formed via chlorine (Cl2) reaction with high purity aluminum pellets. As-grown AlN layers have been characterized by Scanning Electron Microscopy (SEM), X-ray diffraction rocking curves (XRC) and Raman spectroscopy. First, the influence of the V/III ratio in the gas phase on surface morphology, crystalline quality and strain into the material is investigated in order to improve the quality of epitaxial AlN layers grown at high temperature. Parameters were adjusted to keep constant growth rate of about 5 µm/h. Second, a protective layer (growth of a 200 nm-thick AlN layer at 1200 °C) was deposited before the main growth of a 5µm layer of AlN at 1500°C. A 430 arcsec FWHM value for the 0002 reflection of the AlN layer has been obtained for such experimental conditions. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Thin (0001) epitaxial aluminum nitride (AlN) layers were grown on c-plane sapphire using high temperature hydride vapor phase epitaxy. The experimental set-up consists of a vertical cold-wall quartz reactor working at low pressure in which the reactions take place on a susceptor heated by induction. The reactants used are ammonia and aluminum chlorides in situ formed via hydrogen chloride reaction with high purity aluminum pellets. As-grown AlN layers have been characterized by scanning electron microscopy, atomic force microscopy, X-ray diffraction, transmission electron microscopy, photoluminescence and Raman spectroscopies. The influence of the V/III ratio in the gas phase, from 1.5 to 15, on growth rate, surface morphology, roughness and crystalline quality is investigated in order to increase the quality of thin epitaxial AlN layers grown at high temperature. Typical growth rates of around 0.45 μm/h were obtained for such thin epitaxial AlN layers. The growth rate was unaffected by the V/III ratio. An optimum for roughness, crystalline quality and optical properties seems to exist at V/III = 7.5. As a matter of fact, for a V/III ratio of 7.5, best root mean square roughness and crystalline quality — measured on 0002 symmetric reflection — as low as 6.9 nm and 898 arcsec were obtained, respectively. [ABSTRACT FROM AUTHOR]