Growth of thin silicon films on sapphire and spinel by molecular beam epitaxy

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Abstract
Epitaxial silicon films have been grown by molecular beam epitaxy (MBE) on (1̄012) sapphire and (100) spinel substrates. Film morphology and electrical quality are strong functions of substrate preparation and vacuum purity. Under optimized conditions, single‐crystal growth occurs at 650–800 °C and 700–900 °C on sapphire and spinel substrates, respectively. Films initially grow in islands which coalesce and gradually form smooth continuous layers. On sapphire, coalescence occurs at ∼500 Å and films grow smoothly above ∼2000 Å. On spinel coalescence occurs at ∼0.5 μm and smooth growth above ∼1 μm. Thick films on either substrate have mobilities close to bulk. As thickness decreases, mobilities fall gradually and values cannot be measured in films less than twice the coalescence thickness. At thicknesses of 0.5 and 1.0 μm, MBE SOS films have mobilities in excess of those reported for comparably doped CVD layers.