A new analytical approach to amorphous silicon thin film transistors

Abstract

Using both analytical and computer models the I–V characteristics of amorphous silicon (a-Si) thin film transistors are related to the basic material parameters. The characteristic energies of the density of states variations are related to the slope of the current-voltage characteristics in the subthreshold regime. For the acceptor-like states between the Fermi level and 0.15 eV below the conduction band edge we deduce the characteristic energy E ca = 80–100 mV for devices fabricated by various researchers, in good agreement with photoconductivity measurements and other experimental data. Based on the transfer characteristics at voltages above threshold, we determine the temperature dependence of the electron mobility the characteristics energy of the tail states and the contact resistance. Our theory of a-Si thin film transistors predicts how device characteristics scale with gate length, oxide thickness, channel doping, temperature, and material properties. This theory may be used to optimize the design of a-Si thin film transistors.