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Epitaxial Growth of Silicon Films Evaporated on Sapphire

Single-crystal films of silicon with good structural and electrical properties were successfully obtained on 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 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 1017 to 1016holes/cm3 and Hall mobility increases up to 250 cm2/V·sec.

Self-assembled monolayer growth of octadecanoic acid on single-crystal C-plane and R-plane sapphire (α-Al2O3) has been investigated by ex situ tapping mode atomic force microscopy, contact angle measurements, and Fourier transform infrared spectroscopy. Partial monolayers, interrupted during growth, contain islands of a densely packed well-ordered phase within a lower-lying disordered molecular matrix. The areal fraction of the ordered phase increases as a function of immersion time. The growth kinetics are sensitive to the history of the sapphire substrate; e.g., complete monolayers were formed from 1.5 mM hexadecane solution in 1 min on freshly annealed (i.e., dehydrated) substrates in comparison with 1 h on substrates aged for 1 day under ambient conditions. The growth is slightly faster on C-sapphire than R-sapphire. Although weakly bound, the complete monolayers are very well-ordered, conformal, and essentially defect-free.


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