An Amplified Imaging Sensor using a-Si:H Supper-lattice Photoconductive Layer

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Realization of the solid-state imaging sensor having a superior sensitivity over the human vision is important problem for us. To satisfy the demand, following subjects must be solved. a) The device structure with the aperture ratio of 100%. b) Pixel structure which the photo-excited carrier can be amplified in the pixel. c) New photo-electron conversion concept by which quantum efficiency larger than unity can be realized. The important results from this study are following. 1) The amplified solid-state imager overlaid by a-Si:H photodiode layer was implemented and the aperture ratio of 100% was realized. It was shown that the proposed device structure is available to future high definition imager. 2) New device structure using an avalanche multiplication was proposed and the multiplication gain over 100 was obtained. The realization of the solid-state imager having the effective quantum efficiency exceeding unity became possible. 3) An a-Si:H photodiode layer structure, which two regions, the carrier multiplication and the photon absorption can be separated each other, was proposed and the current amplification due to the avalanche multiplication was observed. It was shown that the blocking structure using the a-Si_3N_4 layer is suitable to prevent the hole injection from the electrode. An a-Si:H/a-SiC:H supper-lattice avalanche photodiode layer was also designed and fabricated. High conversion efficiency over unity was confirmed. 4) Spindt field electron emissions with rim geometry was fabricated and the emission levels of up to 40 muA per tip with applied voltage in the 500V range. It was found that the emission levels were larger than that of cone geometry cathode made by same fabrication process. The rim type emission array is the optimum structure applicable to the future solid-state imager.