Monolithic a-SiC:H stack architectures as tunable optical filters for spectral analysis
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1246-B07-08
Monolithic a-SiC:H stack architectures as tunable optical filters for spectral analysis M. Vieira1,2,3, P. Louro1,2, M. A. Vieira1,2, J. Costa1,2, M. Fernandes1,2, Y. Vygranenko1,2, M. Barata1,2 1 Electronics Telecommunications and Computer Dept, ISEL, Lisbon, Portugal. 2 CTS-UNINOVA, Quinta da Torre, 2829-516, Caparica, Portugal. 3 DEE-FCT-UNL, Quinta da Torre, 2829-516, Caparica, Portugal. ABSTRACT The characteristics of a tunable wavelength filter in a-SiC:H multilayered stack p-i'i-n graded cells are studied both theoretically and experimentally. Three different architectures are tested for proper fine tuning of the spectral sensitivity. The simplest configuration is a two terminal p-i-n photodiode where the active intrinsic layer is a double layered a-SiC:H/a-Si:H thin film. In the others the active device consists of a p-i'(a-SiC:H)-n / p-i(a-Si:H)-n heterostructures where the doped layers can have high or low conductivities. The spectral analysis of the device is performed under different optical and electrical applied bias and frequencies. Results show that, depending on the architecture and time window used, the device acts as an optical filter, an amplifier or a multiplexer /demultiplexer for optical signal processing, wavelength conversion, signal demultiplexing and pattern recognition. A theoretical analysis supported by numerical and electrical simulations is presented. The analysis uses simple phototransistor and photodiode equations to explain the response of the device under different optical signals, and to compare the generated photocurrent with the experimental data. INTRODUCTION Tunable optical filters are useful in situations requiring spectral analysis of an optical signal. Light wavelength discrimination depends on the structure of the sensor, on the thickness of each p-i-n cell, and on the selected sequence of cells in the stack structure. A tunable optical device is a device for wavelength selection such as an add/drop multiplexer (ADM) which enables data to enter and leave an optical network bit stream without having to demultiplex the stream. They are often used in wavelength division multiplexing (WDM) systems [1]. WDM systems have to accomplish the transient wavelength recognition of two or more input channels in addition to their capacity of combining them onto one output signal without losing any specificity (wavelength and bit rate). Only the visible spectrum is applied when using polymer optical fiber for communication, so, there is demand of new optical processing devices that work in this region of the spectrum. Results on the optimization of different stack a-SiC:H heterostructures for spectral analysis in the visible spectrum are presented. A theoretical analysis and an electrical simulation is performed to support the wavelength selective behavior. DEVICE CONFIGURATION The semiconductor sensor element is based on single or stacked a-SiC:H p-i-n structures using different architectures, as depicted in Figure 1. All devices were produced by PE-CVD on a glass substrate
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