Thin-film silicon: Preparation, properties, and device applications

This paper will review the properties of thin silicon films deposited on sapphire (SOS) and magnesium aluminate spinel by the pyrolysis of silane in the temperature range 900-1200°C. Variations of carrier mobility, free-carrier concentration, minority carrier lifetime, crystalline perfection, and surface quality will be discussed as a function of substrate crystal and growth parameters. MOS transistors exhibiting field-effect mobility close to that obtained with bulk silicon have been fabricated and a complementary MOS transistor memory cell has been constructed with a WRITE-READ delay of 6 ns. The standby power for the cell is typically 10 µW. Other CMOS circuits display a pair-delay of 1.5-2.0 ns. AIl-epitaxial bipolar transistors with a current gain of 5 and f
T
of 350 MHz have been made in which all layers are sequentially deposited during one high-temperature operation. Recent improvements in bipolar fabrication techniques have lead to current gains as high as 25 at 10 mA.