Structural, optical, and electrical properties of nanocrystalline silicon films deposited by hydrogen plasma sputtering

Nanocrystalline silicon films were deposited by radio frequency sputtering in a pure H-2 plasma on glass and monocrystalline [100] silicon at various substrate temperatures, T-s. The detailed structural, optical, and electrical analysis of the films has been performed by transmission electron microscopy, Raman scattering, infrared spectroscopy, x-ray diffraction, optical absorption, photoluminescence and electrical measurements. The data obtained show that, to a significant extent, control of the structure and hence of the optical and electrical properties of the films can be achieved by changing T-s. Increasing T-s from 50 to 250 degrees C leads to an increase of the average grain size (from a few nm to a few tens of nm) and crystalline fraction (from 37% to 74%) and the optical band gap decreases from 2.40 to 1.95 eV. Hydrogen incorporation, together with T-s, are thought to be at the origin of the resulting microstructure and consequently determine the optical and transport properties, Moreover, hydrogen content was found to be associated with void formation which induces structure relaxation with very low residual stress. Finally, electrical conductivity in the layers increases by more than six orders of magnitude with T-s. The high dark conductivity measured from the sample deposited at the highest T-s (>10(-3) Omega(-1) cm(-1)) and its low activation energy (0.13 eV) are in agreement with the high crystalline fraction of this layer, where tunneling of carriers between the crystallites likely occurs. (C) 1998 American Vacuum Society.