Reviewing Photo-sensing Devices Using a-Sic Based Materials

In this paper a double pi’n/pin a-SiC:H voltage and optical bias controlled device is presented and it behavior as image and color sensor, optical amplifier and multiplex/demultiplex device discussed. The sensing element structure (single or tandem) and the light source properties (wavelength, intensity and frequency) are correlated with the sensor output characteristics (light-to-dark sensivity, resolution, linearity, bit rate and S/N ratio). Depending on the application, different readout techniques are used. When a low power monochromatic scanner readout the generated carriers the transducer recognize a color pattern projected on it acting as a color and image sensor. Scan speeds up to 104 lines per second are achieved without degradation in the resolution. If the photocurrent generated by different monochromatic pulsed channels is readout directly, the information is multiplexed or demultiplexed. It is possible to decode the information from three simultaneous color channels without bit errors at bit rates per channel higher than 4000bps. Finally, when triggered by appropriated light, it can amplify or suppress the generated photocurrent working as an optical amplifier. An electrical model is presented to support the sensing methodologies. Experimental and simulated results show that the tandem devices act as charge transfer systems. They filter, store, amplify and transport the photogenerated carriers, keeping its memory (color, intensity and frequency) without adding any optical pre-amplifier or optical filter as in the standard p-i-n cells.