Band-tail parameter in polysilicon materials

We develop a band-tail model in polysilicon by analyzing the energy band st ructure on the basis of the band-tail parameter with Urbach exponential beh avior due to the trap states and the strain in grain bulks and grain bounda ries. A quantitative analytical formulation for the band-tail parameter E-0 has been deduced by taking into account the carrier-impurity interaction, the carrier-phonon interaction, and the structural disorder. The dependence of E-0 and the electric field F in the grain boundary of polysilicon on ca rrier concentration n(0) and temperature T has been studied within the fram ework of the model. The results indicate that E-0 and F increase with T. Fu rthermore, the increase in E-0 at n(0)=1.0x10(18) cm(-3) is much larger tha n that in E-0 at n(0)=1.0x10(16) cm(-3) at the same temperature. We have de monstrated that the theoretical results are consistent with the experiment, and our model is therefore valuable for both describing polysilicon materi als and improving the performance of polysilicon devices. (C) 2001 American Institute of Physics.