Voltage controlled amorphous Si/SiC photodiodes and phototransistors as wavelength selective devices: Theoretical and el
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Voltage controlled amorphous Si/SiC photodiodes and phototransistors as wavelength selective devices: Theoretical and electrical approaches M A Vieira1,3, M. Vieira1,2, P. Louro1,2, M. Fernandes1, A. Fantoni1, M. Barata1,2 Electronics Telecommunications and Computer Dept, ISEL, Lisbon, Portugal. UNINOVA, Lisbon, Portugal. 3CML-Traffic Department, Lisbon, Portugal. 1
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ABSTRACT In this paper single and stacked structures that can be used as wavelength selective devices, in the visible range are analysed. Two terminal heterojunctions ranging from p-ií-n to p-i-n-p-i’-n configurations are studied. Three terminal double staked junctions with transparent contacts inbetween are also considered to increase wavelength discrimination. The color discrimination was achieved by ac photocurrent measurement under different externally applied bias. Experimental data on spectral response analysis and current –voltage characteristics are reported. A theoretical analysis and an electrical simulation procedure are performed to support the wavelength selective behaviour. Good agreement between experimental and simulated data was achieved. Results show that in the single p-i-n configuration the device acts mainly as an optical switch while in the double ones, due to the self bias effect, the input channels are selectively tuned by shifting between positive and negative bias. If the internal terminal is used, the interwavelength cross talk is reduced and the signal-to-noise ratio increased. INTRODUCTION Application fields of polymer optical fibers (POF) technology is increasing mainly driven by the computing power incidence allied with everywhere multimedia home appliances [1]. Only the visible spectrum can be applied when using POF for communication. So, the demand of new optical processing devices is a request.Wavelength multiplexing devices have to accomplish the transient colour 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 transmission speed) [2]. Light wavelength discrimination depends on the structure of the sensor, thickness of each p-i-n cell, and on the selected sequence of the cells in the multilayer structure. In this paper we present results on the optimization of different multilayered a-SiC:H heterostructures for wavelengthdivision multiplexing applications in the visible spectrum. A theoretical analysis and an electrical simulation procedure are performed to support the wavelength selective behaviour. DEVICE CONFIGURATION Voltage controlled devices, with front and back indium tin oxide transparent contacts were produced by PECVD at 13.56 MHz radio frequency in three different architectures and tested for a proper fine tuning of the visible spectrum. In the first configuration (NC11), the device is a p-i-n photodiode where the intrinsic layer is a multilayered a-SiC:H/a-Si:H thin film. In the others (NC10 and NC12), the devices have an a-SiC:H (p-i-n)/ a-SiC:H(-p) /Si:H(-i)/SiC:H (-n) confi
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