Theory and interpretation of the field‐effect conductance experiment in amorphous silicon

摘要

The field‐effect conductance modulation experiment, performed on vacuum‐evaporated amorphous silicon films, yielded better than three orders of magnitude change in current for both positive and negative gate voltages. The near symmetry of the plots and their change with deposition rate are interpreted in terms of a Cohen‐Fritzsche‐Ovshinsky‐type density‐of‐states model. Calculations are presented for the model that includes the mobile charge and the mobility ratio of the carriers. Results are presented for room as well as for elevated temperatures. The Fermi energy is near the center of the mobility gap and the density of localized states is nearly uniform for ±0.4 eV above and below EF. At energies greater than 0.4 eV away from the Fermi energy, the density of the localized states is modeled by an increasing exponential out to the limit of the experimental data at about ±0.455 eV. The theory and experiment agree at room temperature and over a range of temperatures and sample preparation conditions. The localized states near EF decrease as the deposition rate decreases. A lower limit of from 6×1019 to 2×1020/cm3 eV remains and is sample preparation dependent.