Effective density-of-states distributions for accurate modeling of polycrystalline-silicon thin-film transistors

Abstract

The effective density-of-states (DOS) distributions in unhydrogenated and hydrogenated polycrystalline silicon (poly-Si) thin films have been determined from field-effect conductance measurements of n- and p-channel thin-film transistors (TFTs) fabricated in these films. These results are compared with those obtained through device simulation as well as with trap-state densities obtained by Levinson’s method. Variations in TFT fabrication process conditions and device architecture are shown to significantly impact the DOS distribution and to correspondingly affect device performance. Hydrogenated low-temperature-processed (600 °C) films have relatively high midgap-state and valence-band tail-state densities and Fermi levels located above midgap, in contrast to high-temperature-processed (950 °C) films that have low midgap-state densities and Fermi levels located below midgap. The field-effect conductance analysis method provides realistic gap-state density information and can thereby facilitate the accurate modeling and simulation of TFT device and circuit behavior.