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We present a novel sensor concept comprising a new contacting scheme for voltage-bias con- trolled thin film photodiode arrays on CMOS readout chips. Our unilateral contact structure greatly facilitates manufacturing of the sensor system. Moreover, the novel contacting scheme most efficiently suppresses crosstalk between neighboring pixels. The respective devices are ready for operation and testing directly after deposition of the amorphous silicon based sensor layers. No extra transparent front contact is needed, no patterning and no connection between the topmost layer of the thin film stack and the underlying readout chip. Due to the lack of a metal oxide front contact, contamination of CMOS manufacturing equipment with tin, zinc or similar materials is definitely avoided. Thus, for the first time, a sensor concept with complete CMOS process compatibility is demonstrated. Our new sensor structure allows for a considerable reduction in manufacturing cost of high performance optical detection systems. As a proof of concept, we present detailed investiga- tions on current-voltage characteristics, dynamic behavior and spectral response of 0.1-inch test structures. Down-scaling to pixel sizes in the micron range is evaluated by semi-empirical numerical modeling and proves easily feasible.

The operational principle of a new type p-i-i-n color sensor is described with the aid of numerical modeling. The modeling results account for the color detection mechanism recently presented that this kind of structure exhibits [T. Neidlinger, M. B. Schubert, G. Schmid, and H. Brummack, in Amorphous Silicon Technology—1996, edited by E. A. Schiff et al. (Materials Research Society, Pittsburgh, 1996), p. 147]. By band gap engineering the experimental red response is maximized at larger reverse bias voltage whereas the green response has its maximum at low reverse bias voltage. The numerical modeling qualitatively reproduces the characteristic shape of the steady-state current-voltage curves at different illumination wavelengths. At low and at high reverse bias voltages the influence of the internal variables and parameters is identified and leads to the experimentally observed response. The potential profile of the p-i-i-n structure is of crucial importance to the color detection mechanism. At larger wavelengths the large potential drop across the two highly defective front layers assists recombination in the back part of the device, which thus leads to the drop in the red response at low reverse voltage. For the voltage-dependent shift in spectral sensitivity it is important that photogenerated carriers under green bias illumination are lost by recombination in the front part of the device.

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