Field effect conductance modulation in vacuum−evaporated amorphous silicon films

Abstract

Electron−beam vacuum−deposited amorphous silicon films were deposited at controlled rates from 3.1 to 5.6 Å/sec onto Si−SiO₂ substrates followed by a 4−h 400 °C in situ anneal. The high−temperature activation energy for these films has an average value of 0.79 eV and is relatively independent of the deposition rate. The room−temperature resistivity varies from 3×10⁷ Ω cm at a 5.6 Å/sec rate to 5.7×10⁷ Ω cm at 3.1 Å/sec. The preexponential factor has an average value of 7×10⁻⁵ Ω cm and is independent of the deposition rate. A change in source−drain current due to a transverse electric field was observed at room and elevated temperatures for both positive and negative gate voltages. The results indicate that the Fermi level is not pinned near midgap and that the density of localized states near the Fermi level is nearly uniform for ±0.40 above and below midgap. Calculations indicate that the density of localized states near the Fermi level is about 10²⁰/cm³ eV and decreases slightly as the rate is decreased.