The Production of EFG Sapphire Ribbon for Heteroepitaxial Silicon Substrates

A process is described for the growth of sapphire crystals in a ribbon geometry by the Edge-defined Film-fed Growth (EFG) technique. The ribbon shaped crystals are grown for use as substrates for heteroepitaxial silicon. The apparatus, growth process, and characteristics of the grown ribbon are described. Three ribbons, 75 mm in width, are grown simultaneously. The growth rate is between 152 and 204 mm/h. A high percentage of the ribbons are free of off-oriented grains. The main defect features are “sheet” microvoids typically 5–25 μm in diameter, and “distributed” microvoids typically 0.5–2 μm in diameter. No significant difference is observed in devices fabricated in the heteroepitaxial silicon deposited on EFG and Czochralski grown substrates.

Epitaxial growth of GaN on sapphire substrates using an open-tube growth furnace has been carried out to study the effects of substrate orientation and transfer gas upon the properties of the layers. It has been found that for the (0001) substrates, surface appearance was virtually independent of carrier gas and of doping levels. For the (1 ¯102) substrates surface faceting was greatly reduced when He was used as a transfer gas as opposed to H2. Faceting was also reduced when the GaN was doped with Zn and the best surfaces for the (1 ¯102) substrates were obtained in a Zn-doped run using He as the transfer gas. The best sample in terms of electrical properties for the (1¯102) substrate had a mobility greater than 400 cm2 V−1 sec−1 and a carrier concentration of about 2 × 1017 cm−3. This sample was undoped and used He as the transfer gas. The best (0001) sample was also grown undoped with He as the transfer gas and had a mobility of 300cm2V−1 sec−1 and a carrier concentration of 1 × 1018 cm−3.


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