Epitaxial Growth of Silicon Films Evaporated on Sapphire

Single-crystal films of silicon with good structural and electrical properties were successfully obtained on (000, 1) sapphire substrates by evaporation in a vacuum of about 2×10 -6 torr. Silicon was evaporated at a high deposition rate of 1500 Å/min, using a specially-designed electron bombardment apparatus. The growth process was investigated by reflection electron diffraction and replica techniques. The initial deposits contain four preferred orientations, all with (111) parallel to the substrate surface. Upon further deposition, one of the four orientations develops and a single-crystal film is eventually formed at a film thickness of about 800 Å. It is found that the recrystallization effect occurring on early coalescence of nuclei is essential to the growth of single-crystal films. Electrical properties were measured for the films, 0.7 to 6.1 µm thick. With increasing film thickness, carrier concentration decreases from 10 17 to 10 16 holes/cm 3 and Hall mobility increases up to 250 cm 2 /V·sec.