Low temperature epitaxial growth of widegap semiconductors using reactive radicals and high-energy precursors generated by catalytic reactions

Abstract

Summary form only given. Chemical vapor deposition (CVD) methods are widely used for the growth of thin films in the mass production of electronic devices, because CVD has technical advantages such as high growth rates over large surface areas, a wide selection of source materials, ease of purification by evaporation, and low-cost production. However, films obtained by CVD are inferior to those grown by molecular beam epitaxy or pulse laser deposition. In addition, conventional CVD methods consume a large amount of electric power to enable reaction of the source gases and to increase the substrate temperature for the deposition of high-quality thin films. The ideal method for growing high quality films for electronic devices is the CVD method accompanied by excitation of the source gases or the generation of high-energy precursors and reactive radicals using energy-saving methods. CVD that employs catalytic reactions is one of the most effective methods to realize these objectives. We have been studying new CVD methods involving catalytic reactions for the growth of a variety of electronic materials under resourceand energysaving conditions. In this presentation, some CVD methods for the epitaxial growth of widegap semiconductors such as SiC, GaN and ZnO are reported. For the growth of SiC epitaxial films, a high concentration of hydrogen radicals generated on a heated tungsten mesh were transferred onto the growing film surface in order to extract bonded hydrogen from the adsorbed organosilicon compounds, which are the source gases for SiC growth. SiC films were epitaxially grown on Si and SOI substrates at a low temperature of 750°C using this technique. In a similar manner, GaN films were grown with a low NH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /TMAI gas ratio of less than 100, using a high concentration of NH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> radicals generated on a heated tungsten mesh which was coated with a Ru thin film. In addition, ZnO epitaxial films could be grown on α-face sapphire substrates using high-energy water molecules generated by the self-exothermic reaction between H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> on platinum nanoparticles dispersed on ceramic granules. Using this CVD method, excellent quality epitaxial ZnO films exhibiting a high electron mobility of 168 cm2/Vs and a low residual carrier density of ~10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">17</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> were grown at 500-600°C.