Wide spectral sensitivity of monolithic a-SiC:H pi'n/pin photodiode outside the visible spectrum

In this paper, we experimentally demonstrate the use of near-ultraviolet steady state illumination to increase the spectral sensitivity of a double a-SiC/Si pi’n/pin photodiode beyond the visible spectrum (400 nm-880 nm). The concept is extended to implement a 1 by 4 wavelength division multiplexer with channel separation in the visible/near infrared ranges. The device consists of a p-i'(a-SiC:H)-n/p-i(a-Si:H)-n heterostructure, sandwiched between two transparent contacts. Optoelectronic characterization of the device is presented and shows the feasibility of tailoring the wavelength and bandwidth of a polychromatic mixture of different wavelengths. Results show that the spectral current under steady state ultraviolet irradiation depends strongly on the wavelength of the impinging light, and on the background intensity and irradiation side allowing controlled high-pass filtering properties. If several monochromatic pulsed lights, in the visible/near infrared (VIS/NIR) range, separately or in a polychromatic mixture illuminate the device, data shows that, front background enhances the light-to-dark sensitivity of the medium, long and infrared wavelength channels, and quench strongly the low wavelengths channels. Back background has the opposite behavior; it enhances only channel magnitude in short wavelength range and strongly reduces it in the long ones. This nonlinearity provides the possibility for selective tuning of a specific wavelength. A capacitive optoelectronic model supports the experimental results. A numerical simulation is presented.