THIN-FILM PHOTOSENSOR DESIGN FOR LIQUID-CRYSTAL SPATIAL LIGHT MODULATORS

Liquid crystal (LC) spatial light modulators (SLMs) are addressed opti cally with semiconductor thin-film photosensors incorporated into the devices. Nematic LCs, which are insensitive to the polarity of the app lied voltage, are addressed by optically modifying the effective resis tance of the photosensors to be much smaller than or much larger than a threshold value. Much faster ferroelectric LCs, which are polarity s ensitive, are addressed by supplying sufficient photogenerated charge. Because the spatial resolution of the devices decreases rapidly with increasing mobility of carriers at the photosensor/LC interface, very low mobilities, less than 1 cm2 V-1 s-1, are required. Photodiodes of hydrogenated amorphous silicon in p-i-n, Schottky, and metal insulator semiconductor configurations form practical photosensors for opticall y addressed SLMs. Thin-film photoconductors, having nonblocking contac ts, cannot be used in many cases because of their large dark currents.