Improvement in pinpin Device Architectures for Imaging Applications
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Improvement in pinpin Device Architectures for Imaging Applications P. Louro1,2, A. Fantoni1, M. Fernandes1, G. Lavareda3,4, N. Carvalho3,4, and M. Vieira1,2 1 DEETC, ISEL, R. Conselheiro Emídio Navarro, 1, Lisbon, 1959-007, Portugal 2 CTS, Uninova, Monte da Caparica, Caparica, 2829-516, Portugal 3 DCM, Caparica, 2829-516, Portugal 4 IST, C1, Lisboa, 1049-001, Portugal ABSTRACT In this paper we present results on the optimization of device architectures for color and imaging applications, using a device with a TCO/pinpi’n’/TCO configuration. A set of different devices with different intrinsic back layers (i’) are analysed. The effect of the applied voltage on the color selectivity is discussed. Results show that the spectral response curves demonstrate rather good separation between the red, green and blue basic colors. Combining the information obtained under positive and negative applied bias a color image is acquired without color filters or pixel architecture. A low level image processing algorithm is used for the color image reconstruction. INTRODUCTION The use of multilayered structures based on a-SiC:H alloys as color sensors has been an important topic of research in the field of sensing applications [1, 2, 3]. In these multilayered devices the light filtering is achieved through the use of different band gap materials, namely aSi1-xCx:H. In these devices the spectral sensitivity in the visible range is controlled by the external applied voltage. Thus, proper tuning of the device sensitivity along the visible spectrum allows the recognition of the absorbed light wavelength, and consequently the identification of the RGB components of a colored image [4]. In this paper color pinpi’n’ sensitive detectors are tested using the laser scanned photodiode technique (LSP) [5]. This technique allows a complete color analysis to be performed with a single two terminal detector element and an optically addressed readout technique. The image to acquire is optically mapped onto the sensing photodiode and a low-power light spot scans the device by the opposite side. The photocurrent generated by the moving spot corresponds to the image signal as its magnitude depends on the light pattern localization and intensity. For image color acquisition the device is biased at different voltage values, which modulates the output image signal and allows the reconstruction of the color image [6, 7]. EXPERIMENTAL DETAILS Device Architecture A series of stacked devices are analyzed in this work. The front p-i-n structure is common to all devices while the thickness of the back intrinsic absorber layer was varied in order to optimize the device. The geometry of the stacked sensors is sketched in Fig. 1. The sensor is a double heterostructure device and consists of a glass/ITO/p-i-n a-SiC:H photodiode which faces
Bias voltage (V)
Optical readout (scanner)
TCO a-Si:H (n type)
Back Photodiode V2
a-Si:H (i’ type)
#NC4: 500 nm #NC5: 1000 nm #NC7: 1500 nm
a-SiC:H (p type) a-SiC:H (n type) Front Photodiode V1
a-SiC:H (i typ
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