Amorphous semiconductors for optoelectronic applications: photoconductors, detectors and sensors based on se-alloys

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Amorphous semiconductors, such as hydrogenated amorphous silicon (a-Si:H) and its alloys, amorphous selenium (a-Se) and its alloys (a-Se:As) etc, have one clear distinct advantage over crystalline semiconductors that they can be conveniently fabricated over large areas, which has lead to their extensive commercial use in photovoltaics, flat panel displays (TFT displays), flat panel x-ray image detectors, and flexible electronics. Within the field of electronic and optoelectronic devices, amorphous semiconductors represent a particularly important niche in which Canada has a very strong and competitive presence. Our long term goals and objectives are to build on strength by expanding our scientific and technological knowledge on a-Se alloy based semiconductors and optoelectronic devices by innovation at the material level, innovation at the device level and advancing knowledge at the fundamental level. The design of next generation a-Se x-ray image detectors also needs extensive knowledge on the electrical properties of the photoconductor used in the three layers, e.g. charge carrier ranges, drift mobility x carrier lifetime, excess noise and thermal generation rate in each layer. To date, no one has examined the nature of electronic noise in a-Se p-i-n detectors and we intend to take this on as a major study. Our objectives and studies will include: (i) Discovering and understanding the electrical and optoelectronic properties of a-Se:As alloys as a function of temperature and electric field toward enhanced p-i-n structures with lower dark currents and higher applied fields; increasing the field will improve the DQE. (ii) Discovering the behavior of low-frequency (1/f) noise for better detector design. (iii) More stable compositions for the i-layer and p-layer through enhanced material properties from (i). (iv) Developing avalanche a-Se structures with multiplication, demonstrating their suitability for use in ultrasensitive optical imaging and in indirect radiation detection. The impact of the work is, of course, the generation of new knowledge on a-Se detectors, novel structures with new compositions, for the design and development of next generation a-Se x-ray detectors, and all solid state ultrasenstive optical image sensors.