Relationship between a-Si:H band tails and TFT performance

Inverted-staggered a-Si:H/a-SiN/sub x/:H TFTs and separate a-Si:H films of varying quality were deposited by plasma-enhanced chemical vapor deposition (PE-CVD). The films were extensively characterized, and we found that of all measured properties, the CPM-measured Urbach energy, or valence band tail slope, most significantly correlated with TFT performance, namely with the field-effect mobility. Subsequent modeling of our TFTs revealed that the conduction band tail slope also correlates well with TFT mobility. This suggests a relationship between the Urbach energy and the slope of the conduction band tail. Which in turn determines the TFT mobility. Furthermore, the good agreement between our data and the model, using tail slope values that agree with those measured elsewhere on bulk a-Si:H suggest that the conducting channel for these TFTs is "bulk a-Si:H-like".