Spectral Sensitivity and Color Selectivity in Multilayer Stacked Devices
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A9.2.1
Spectral Sensitivity and Color Selectivity in Multilayer Stacked Devices 1 P. Louro, 1M. Vieira, 1A. Fantoni, 1M. Fernandes, 2,3G. Lavareda, 2,3C. Nunes de Carvalho 1 Electronics Telecommunications and Computer Dept., ISEL, Lisbon, Portugal. 2 C1, IST, Av. Rovisco Pais, 1049-001 Lisboa, Portugal 3 DCM, FCT-UNL, Quinta da Torre, 2829-516 Caparica, Portugal ABSTRACT In this work, an attempt of full color discrimination is presented using as sensitive devices multilayer stacked structures (p(SiC:H)/i(SiC:H)/n(SiC:H) /p(SiC:H)/i(Si:H)/n(Si:H)) sandwiched between two transparent conductive contacts. The thickness and the absorption coefficient of the front p-i-n cell is optimized for blue collection and red transmittance and the thickness of the back one adjusted to achieve full absorption in the green and high collection in the red spectral ranges. The current-voltage characteristics and the spectral sensitivity under different electric and optical bias conditions and light fluxes are analyzed. Results show that color selectivity is achieved by tuning the spectral sensitivity at different applied voltages. A physical model supports the results.
INTRODUCTION The image-sensing device is an apparatus for transforming light image into a sequential electronic signal. They are usually based on arrays of sensing elements. They capture light on a grid of small pixels on their surfaces and the image sensing is performed using two basic techniques: line scanning and area scanning [1, 2]. Resolution is not the only factor governing the quality of the images. Equally important is the color. Silicon based devices present a broad spectral response, and the color image detection is usually performed with the aid of three sequential color filters or integral color filter arrays overlaying the devices. At this respect, voltage controlled color detection by two-terminal thin film devices is very interesting as one instead of three or four pixels will be sufficient for color discrimination, which results in a remarkable gain in spatial resolution and in color filters as a major cost driver. Various structures and sequences have been suggested [3, 4, 5, 6]. In our group large area hydrogenated amorphous silicon single and stacked p-i-n structures with low conductivity doped layers were proposed as Laser Scanned Photodiode (LSP) image sensors [7, 8, 9]. These sensors are different from the other electrically scanned image sensors as they are based on only one sensing element with an opto-mechanical readout system. In this work, an attempt of full color discrimination is presented. The sensitive devices are multilayer stacked structures (p(SiC:H)/i(SiC:H)/n(SiC:H) /p(SiC:H) /i(Si:H)/n(Si:H)) sandwiched between two transparent conductive contacts. Color selectivity is achieved through the modulation of one or both cell depletion regions by an external applied voltage.
EXPERIMENTAL DETAILS Sensor configuration and optical characterization The optically addressed color sensor consists on two stacked p-i-n sensing photodiodes and two s
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