Effects of ion energy on the crystal size and hydrogen bonding in plasma-deposited nanocrystalline silicon thin films

We present a detailed study of the effects of the substrate temperature, radio-frequency (rf) power, and total pressure on the crystal size and hydrogen bonding in nanocrystalline silicon thin films codeposited on the grounded and rf electrodes of an asymmetric radio frequency glow discharge reactor. Raman spectroscopy, x-ray diffraction, and spectroscopic ellipsometry measurements show that by varying the deposition parameters we can obtain crystal sizes in the range of 3-10 nm and crystalline fractions in the range of 20% up to 97%. The obtaining of small crystallite sizes (4-5 nm) in films submitted to high-energy (100-300 eV) ion bombardment is highlighted by infrared-absorption and hydrogen evolution measurements, which display characteristic features of hydrogen bonded at the surface of the crystallites. Therefore, hydrogen bonding is a unique way to demonstrate the presence of small crystallites in films at the transition between amorphous and nanocrystalline, films which look amorphous when characterized by standard techniques such as Raman spectroscopy and x-ray diffraction.