High performance thin-film transistors with low-high-low band gap engineering

Abstract

A novel high-performance thin-film transistor (TFT) with low-high-low band gap structure is proposed. We propose a novel device structure combined with low-band-gap materials (microcrystalline Si, mu c-Si:H) for the channel region, high-band-gap materials (hydrogenated amorphous silicon, a-Si:H) for the source and drain offset regions, and heavily doped low-bandgap materials (n(+) a-Si:H) for ohmic contact of source and drain electrodes. We found that, as compared to a-Si:H TFT device with conventional inverted-stagger structures, the device with low-band-gap materials in the channel (e.g. mu c-Si:H) which possesses high conductance can effectively improve the film quality of initial growth active layer near the gate insulator interface and the grown layer. Hence the TFT device parameters such as field effect mobility, threshold voltage, subthreshold swing and ON-current have been significantly improved. This proposed novel structure with high-band-gap material is used to prevent the band to band tunneling and alleviate the high OFF-current in conventional mu c-Si:H thin-film transistors. The proposed high performance TFTs with low-high-low band gap structure will have a great impact in application to high resolution thin-film transistor liquid-crystal displays (TFT-LCDs) and active-matrix liquid-crystal displays (AMLCDs).