Abstract: Liquid crystal (LC) optically addressed spatial light modulators (OASLMs) have been successfully addressed with semiconductor thin film photosensors. Nematic liquid crystals (NLCs), which are insensitive to the polarity of the applied voltage, are addressed with photoconductive thin film structures having symmetric current-voltage characteristics. Much faster ferroelectric liquid crystals (FLC), which are polarity sensitive, are addressed with asymmetric photodiodes or photoconductive diodes. The highest performance OASLMs have been fabricated using FLCs and a-Si:H photodiodes as the photosensor. In this paper we analyze the role of the thin film photosensor in a LC OASLM and present design criteria. From these criteria we discuss hydrogenated amorphous silicon (a-Si:H) photosensor structures for use in OASLMs. In particular we review the a-Si:H p-i-n photodiode, the transparent conducting oxide (TCO)/intrinsic a-Si:H photoconducting diode, and the metal/insulator/a-Si:H structures which have been successfully incorporated into FLC OASLMs, and the n-i-n photoconductor which has not.!26
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