Grain-boundary-limited carrier mobility in polycrystalline silicon with negative temperature dependence: Modeling carrier conduction through grain-boundary traps based on trap-assisted tunneling

Abstract

Seto's model based on thermionic emission (TE) theory explains that the grain-boundary (GB)-limited carrier mobility in polycrystalline silicon (poly-Si) has a positive temperature dependence. Although this model is widely accepted as a standard model for GB-limited carrier mobility in poly-Si, many experimental measurements under steady-state conditions support extremely weak or negative temperature dependence. In this report, we formulate carrier conduction through GB traps by utilizing the trap-assisted tunneling (TAT) model based on non-radiative multi-phonon transition theory. Self-consistent calculation of poly-Si under steady-state conditions reveals that TAT current exceeds TE current in regions with high GB potential barriers. In contrast to Seto's model, our novel model reproduces the negative dependence of GB-limited carrier mobility on temperature. From the viewpoint of consistency with experimental measurements, our model seems to be suitable for describing carrier conduction in poly-Si under steady-state conditions.