فیلتر کردن رنگ در H :a-SiC مبتنی بر سلول هایp-i-n-p-i-n : تجاری کردن بین قطب تعصب و مناطق جذب

A large area colour imager optically addressed is presented. The colour imager consists of a thin wide band gap p-i-n a-SiC:H filtering element deposited on the top of a thick large area a-SiC:H(-p)/a-Si:H(-i)/a-SiC:H(-n) image sensor, which reveals itself an intrinsic colour filter. In order to tune the external applied voltage for full colour discrimination the photocurrent generated by a modulated red light is measured under different optical and electrical bias. Results reveal that the integrated device behaves itself as an imager and a filter giving information not only on the position where the optical image is absorbed but also on it wavelength and intensity. The amplitude and sign of the image signals are electrically tuneable. In a wide range of incident fluxes and under reverse bias, the red and blue image signals are opposite in sign and the green signal is suppressed allowing blue and red colour recognition. The green information is obtained under forward bias, where the blue signal goes down to zero and the red and green remain constant. Combining the information obtained at this two applied voltages a RGB colour image picture can be acquired without the need of the usual colour filters or pixel architecture. A numerical simulation supports the colour filter analysis.

Red, green and blue (RGB) are the additive fundamental perceptual components of the visible spectrum and can be easily separated by using appropriate detectors and/or bandpass filters [1] and [2]. Light filtering, employing distinct wavelength optimized structures, in an array, is rather complex and is an expensive solution. Optical filters may be eliminated by using a-SiC:H multi-layer stacked devices, in which the detector structure, itself, behaves as a filter. In the stacked structure, information about the spectrum corresponds to information about where the radiation is absorbed. By sampling the absorption region with different bias voltages, and extracting separately the integrated information about the radiation absorbed in each region is possible to identify the RGB components of the visible spectrum [3], [4], [5] and [6]. In those devices, blue light is usually detected in the front of the structure, green light at the centre and red light at the bottom. Large area single and stacked p-i-n image sensors based on amorphous hydrogenated silicon alloys were proposed as optically addressed laser scanned photodiode (LSP) [7] and [8]. The LSP sensor is different from the electrically scanned image systems since it is based on one single sensing element, and uses a modulated low-power beam of laser light to scan the active area directly. Advantages to this approach are large area imaging, high resolution and uniformity of measurement along the sensor. The complexity of the interconnection is reduced, while the colour information is extracted by applying a sequence of test voltages. In this paper, we propose to optimize the sensor design in order to apply the optical addressed Laser Scanned Photodiode technique to full colour discrimination. The effect of the applied voltage on the colour selectivity and image intensity is discussed and supported by a self-biasing model.

Light filtering using the Laser Scanned Photodiode technique in a-SiC:H multi-layer devices was presented and explained through a trade-off between the different light penetration depth of the impinging photons and self adjustments of the electrical field. Results show that the colour discrimination and the light-to-dark sensitivity are dependent on the thickness of the back absorber and on the readout voltage. For each red, green and blue wavelength colour rejection was achieved at a readout voltage that cancels the self-bias effect in the back absorber. This voltage shifts from reverse to forward as the light penetration depth in the back diode decreases.