Results on the use of a double a-SiC:H p–i–n heterostructure for signal multiplexing and demultiplexing applications in the visible range, are presented.
Modulated monochromatic beams together ...(multiplexing mode), or a single polychromatic beam (demultiplexing mode) impinge in the device and are absorbed, accordingly to their wavelength, giving rise to a time and wavelength dependent electrical field modulation.
Red, green and blue pulsed input channels are transmitted together, each one with a specific transmission rate. The combined optical signal is analyzed by reading out, under different applied voltages, the generated photocurrent. Results show that in the multiplexing mode the output signal is balanced by the wavelength and transmission rate of each input channel, keeping the memory of the incoming optical carriers. In the demultiplexing mode the photocurrent is controlled by the applied voltage allowing regaining the transmitted information. An electrical model gives insight into the device operation.
In this paper we demonstrate an add/drop filter based on SiC technology. Tailoring of the channel bandwidth and wavelength is experimentally demonstrated. The concept is extended to implement a 1 by ...4 wavelength division multiplexer with channel separation in the visible range. The device consists of a p-i'(a-SiC:H)-n/p-i(a-Si:H)-n heterostructure. Several monochromatic pulsed lights, separately or in a polychromatic mixture illuminated the device. Independent tuning of each channel is performed by steady state violet bias superimposed either from the front and back sides. Results show that, front background enhances the light-to-dark sensitivity of the long and medium wavelength channels and quench strongly the others. Back violet background has the opposite behaviour. This nonlinearity provides the possibility for selective removal or addition of wavelengths. An optoelectronic model is presented and explains the light filtering properties of the add/drop filter, under different optical bias conditions.
In this paper we present results on the optimization of an pinpii‘n’ type a-Si:H based three color detector with voltage controlled spectral sensitivity. The sensor element was fabricated on a glass ...covered with Indium Tin Oxide (ITO) and consists of a p-i-n a-SiC:H multilayer structure which faces the incident illumination, followed by a-SiC:H(-p)/a-SiC:H(-i)/a-Si:H(-i′)/a-SiC:H(-n′)/ITO heterostructure, that allows the optically addressed readout.
Results show that this approach leads to regionally different collection parameters resulting in multispectral photodiodes. In the polychromatic operation mode different sensitivity ranges are programmed by switching between different biases so that the basic colors can be resolved with a single device. Positive bias is needed under blue irradiation and moderated reverse bias under green. The threshold voltage between green and red sensitivity depends on the thickness of the bottom a-SiC:H (-i) layer, and corresponds to the complete confinement of the absorbed green photons across the pinpi sequence. As the thickness of the a-Si:H i'-layer increases, the self-reverse effect due to the front absorption will be balanced by the decrease of the self-forward effect due to the back absorption shifting the threshold voltage to lower reverse bias.
The various design parameters are discussed and supported by a 2D numerical simulation.
The present paper reports the optical properties of multilayer structures composed by p-i-n cells based on a-SiC:H or a-Si:H material. Different structures are studied in order to obtain image ...sensors that accomplish color filtering in addition to image pattern recognition. A simple theoretical model is developed to explain sensors behavior and to derive the optical-readout experimental procedure. Electrical models for the sensors are established for simulation purposes and to compare photocurrent signals with experimental data. A numerical simulation of the JV characteristic and of the spectral response is also presented in order to show possible future optimization of the device. Two main structures are studied, namely p-i-n/p-i-n and p-i-n/n-i-p tandem cells.
A SPICE model of the three color a-SiC:H/a-Si:H p–i–n/p–i–n detector operation is presented. The equivalent electric circuit able to describe the behavior of the multilayer structure under ...non-uniform illumination is composed of two series connected diodes, representing the p–i–n structures, with two non-linear current sources in parallel, representing the photogeneration for different steady-state RGB illumination, with their values depending on the light penetration depth and intensity of the impinging light. This device represents the 1D model of the Laser Scanned Photodiode and may be interconnected in a 2D array trough resistors, modeling the high resistivity of the a-SiC:H layers. Electrical simulations were performed for different illumination conditions, and they are compared with the experimental data. The influence of the electrical model parameters on sensor characteristics is analyzed. A physical model supported by the electrical simulation gives insight into the methodology used for image representation and color discrimination.
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