Monolithic a-SiC: H architectures as tunable optical filters for spectral analysis

Characteristics of a tunable wavelength filter in a-SiC:H multilayered stacked p-i'i-n graded cells are studied both theoretically and experimentally. Three different architectures are tested for a 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 were the doped layers can have high or low conductivities. The spectral analysis of device is performed under different optical and electrical applied bias and frequencies. Results show that, depending on the architecture and on the time window used, the devices can be used as optical filter, amplifier or 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 required effects, under different optical signals, and to compare the generated photocurrent with the experimental data.