Bias sensitive multispectral structures for imaging applications

• Published in: Thin solid films Vol. 515; no. 19; pp. 7566 - 7570
• Main Authors: Vieira, M., Fantoni, A., Fernandes, M., Louro, P., Lavareda, G., Carvalho, C.N.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Lausanne Elsevier B.V 16.07.2007; Elsevier Science
• Subjects: a-SiC:H multilayers; Applied sciences; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Electronics; Exact sciences and technology; General equipment and techniques; Image sensors; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Modelling and simulation; Optical properties; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Optical properties of specific thin films; Optoelectronic devices; Physics; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing; Image sensors; Modelling and simulation; a-SiC:H multilayers; Optical properties; Voltage threshold; Radiation effects; Confinement; Multilayer; Digital simulation; Theoretical study; Silicon carbides; Photodiodes; Switching; Optimization; Tin oxides; Multilayers; Imaging; Amorphous hydrogenated material; Detectors; Illumination; Sensors; Indium oxides; Heterostructures
• ISSN: 0040-6090; 1879-2731
• DOI: 10.1016/j.tsf.2006.11.149

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.