High-quality homo-epitaxial silicon growth in a non-ultra-high vacuum environment by ion-assisted deposition

Eliminating the requirement of ultra-high vacuum (UHV) conditions and achieving high-rate crystalline silicon (c-Si) growth are important targets for cheap mass production of semiconductor devices such as thin-film solar cells. In this paper, we report on the achievement of high-quality, high-rate, epitaxial Si growth on Si wafer substrates in a non-UHV environment (base pressure about 1×10 −8 Torr) at low temperatures (440–830°C) by ion-assisted deposition. Impurity contamination in the growing Si film is reduced to tolerable levels by high-rate growth, whereas substrate surface related contamination problems are controlled by the use of a sacrificial protective surface film in combination with a carefully optimised sample heating procedure. Two types of removal of the sacrificial layer from the substrate surface (a high-temperature method and a low-temperature method) are investigated. Thin-film solar cells epitaxially grown on (1 0 0)-oriented Si wafer substrates are used as test vehicles to demonstrate that both substrate surface treatments enable the growth of device-grade Si material in a non-UHV environment.