STRUCTURAL, OPTICAL, AND ELECTRICAL-PROPERTIES OF NANOCRYSTALLINE SILICON FILMS DEPOSITED BY HYDROGEN PLASMA SPUTTERING

Nanocrystalline silicon films were deposited by radio frequency sputte ring in a pure H-2 plasma on glass and monocrystalline [100] silicon a t various substrate temperatures, T-s. The detailed structural, optica l, and electrical analysis of the films has been performed by transmis sion electron microscopy, Raman scattering, infrared spectroscopy, x-r ay diffraction, optical absorption, photoluminescence and electrical m easurements. The data obtained show that, to a significant extent, con trol of the structure and hence of the optical and electrical properti es of the films can be achieved by changing T-s. Increasing T-s from 5 0 to 250 degrees C leads to an increase of the average grain size (fro m 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 an d transport properties, Moreover, hydrogen content was found to be ass ociated with void formation which induces structure relaxation with ve ry low residual stress. Finally, electrical conductivity in the layers increases by more than six orders of magnitude with T-s. The high dar k 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 t unneling of carriers between the crystallites likely occurs. (C) 1998 American Vacuum Society.