Multispectral Structures for Imaging Applications

Results on the optimization of an pinpii 'n type a- Si:H based three color detector with voltage controlled spectral sensitivity are presented. The sensor element consists of a glass/ITO/p-i-n a-SiC:H multilayer structure which faces the incident illumination, followed by a-SiC:H(-p)/a-SiC:H(-i)/Si:H(-i ')/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, coding for red (R), blue (B), and two green (G) components. In the polychromatic operation mode different sensitivity ranges are selected 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 pinpin sequence. The various design parameters are discussed and supported by a 2D numerical simulation.