Three-color sensor based on amorphous n-i-p-i-n layer sequence

We present an amorphous silicon-based n-i-p-i-n three-color sensor with a layer sequence of substrate/metal/n-i-p-i-n/transparent contact. The color sensitivity (red, green and blue) is realized by applying small bias voltages within ±2 V. For the first time, this structure offers the possibility to integrate a color sensor on top of an ASIC chip, where pixel-based signal processing can be performed. Film thickness and optical band gap of the individual layers have been optimized to achieve maximum color separation. The surface of the metal-back contact is found to be critical for the performance of the sensor. A rough surface of the metal is responsible for short circuits at the common p-contact of the back-to-back p-i-n junction diodes. The steady-state I-V characteristics of the dark and photo currents have been studied. The dynamic range of the sensor is already suitable for optoelectronic applications. Sensor performance is not affected by metastable effects after prolonged light soaking. Speed limitations have been evaluated from switching experiments in the voltage mode.