SUPPER-SENSITIVE IMAGING SENSORS USING AVALANCHE MULTIPLICATION PHOTOCONDUCTIVE FILMS AND MICR-FIELD-EMISSION CATHODE ARRAYS

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To realized the supper-sensitive imaging sensors, avalanche multiplication pin photodiode using amorphorus silicon films and micr-field-emission cathodes were investigated. As a result, the following facts become clear.1. The photocurrent amplification in a-Si : H films is caused by impact-ionization of electrons. The amplification gain is limited by carrier scattering effect under high temperature operation and by geminate-recombination mechanism under low temperature region, respectively. The boundary between these temperature regions is determined, depending upon the condition of a-Si : H films. 2. There is two dominant mechnisms as a origin of a dark current in a-Si : H films. One is to be generated through the interface states existing on the interface between silicon substrate and a-Si : H filme. The dark current has temperature dependence and dominates at low bias voltage. Another is tunnel current flowing through trap states lie across the fobidden gap of a-Si : H layr, that is dominant at high electric field. 3. p-type a-SiC : H/i-type a-Si _<1-x>C_x : H/n-type crystalline Si photodiode having conduction-band step DELTA E_c between a-Si_<1-x>C_x : H and crystalline Si is prepared and it is found that at DELTA E_c*0.4eV avalanche gain is two ; each electron assisted by conduction-band discontinuous impact-ionizes once after the conduction-band step. Moreover, three graded-gap supper lattice photodiode (a-Si : H/a-Si_<1-x>C_x : H structure) is studied and at DELTA E_c=0.45eV maximum photocurrent gain of 6.4 was obtained. 4. Novel vilcano type emitters deposited under well-contoroled pressure is investigated. maximum field emission current larger than 750nA was observed from the rims having daimeter of 5 mu m. The value of this emission current is enough to drive the imaging sensors.New, we hasten the implementation of supper-sensitive imaging sensors.