Characterization of Trap States Distribution in Poly-Si TFTs Using OEMS

Opto-Electronic Modulation Spectroscopy (OEMS)technique is applied on polycrystalline silicon thin-film transistors (poly-Si TFTs) to investigate the distribution of bandgap states at grain boundary (GB). Both the current and the phase response spectrums are obtained by analyzing the position and characteristic of gap states at GB. Four discrete bulk trap states in 0.25 eV, 0.45 eV, 0.59 eV, 0.76 eV below conduction band and one continuous interface state in band tail between 1.04 eV and 1.2 eV are determined. All of them are donor-like state except the state in 0.25 eV is acceptor-like. The obtained results are in good agreement with known results by other measurements, both the state location and the property of the state. The present work shows that OEMS technique is a comprehensive and direct way to characterize GB gap states distribution in poly-Si TFTs.