The Structure of Silicon Thin Films Grown on Sapphire by MBE

From a series of imaging experiments performed in the transmission electron microscope (TEM), it is apparent that for silicon grown on sapphire (SOS) by molecular beam epitaxy (MBE), silicon thin film growth on the (1012) sapphire plane resembles that observed for analogous films grown by chemical vapor deposition (CVD). At 900°C very thin (150A) silicon films grow as islands with either the (001) or (110) planes parallel to the (1012) plane; it is also found that most of the silicon grows as (001) rather than (110) islands, as is true for CVD-grown SOS. The orientation, however, of (110) islands occuring in this MBE-grown SOS sample differs from that of (110) islands occuring in CVD-grown SOS. By following this initial 150A of growth with 2500A of silicon deposited at. 750°C, a continuous (001) film was grown in which microtwins appear to be the predominant defect. The MBE-grown SOS also resembles that grown by CVD in that the microtwin densities associated with the “majority” and “minority” twinning systems are influenced by the orientation of the sapphire substrate.