Absorption Enhancement in an Amorphous Silicon Using a Cluster of Plasmonic Hollow Ring Nano-Antennas Abdalem A. Rasheed 1(&) , Khalil H. Sayidmarie 2 , and Khalid Khalil Mohammed 1 1 Department of Electrical Engineering, College of Engineering, Mosul University, Mosul, Iraq abdalemraseed@yahoo.com,kalid.kaleel@yahoo.com 2 Department of Communication Engineering, College of Electronic Engineering, Ninevah University, Mosul, Iraq kh.sayidmarie@gmail.com Abstract. Enhancement of absorption and extending its bandwidth is of major interest for solar cells, photodetectors, and variety of applications. This paper presents a nano-structure formed of an array whose elements are in the form of a 3X3 cluster of metal rings having a similar outer diameter but with various inner diameters. Thus, each ring size produces certain resonance frequency and the result of the cluster arrangement is staggered responses that possess larger band- width. Simulations using the periodic unit cell approach and the CST microwave studio suite showed that the average absorption power in an amorphous silicon layer has been improved by 3.32 times compared to that without rings. The obtained response covers the frequency range from 230 THz to 360 THz. Keywords: Plasmonic  Nanoantennas  Absorption  Amorphous Si 1 Introduction Surface plasmon resonances in nano-antennas are of interest for solar cells, photo detectors, and other various applications because of the large enhancement of the electromagnetic field, which occurs in the vicinity of the metal surface. The resonance frequency of nano-antenna depends on the size, shape, dielectric environment, and dispersion properties of the used metal [1, 2]. There have been significant efforts aiming to increase the light absorption in photovoltaic (PV) layers, spectroscopic, biomedical, and other optical applications. Robust and versatile light absorption using plasmonic aluminum nanorods [3], and effective coupling of light into an S-shape plasmonic silver nanowire waveguide [4] have been reported recently. The use of plasmonic bowtie nanoantennas has shown absorption enhancement and efficient operation over a wide spectrum [5]. In this work, a new structure of Hollow Ring Nano Antennas (HRNAs) distributed at the surface of a thin layer of amorphous silicon (a-Si) is proposed to enhance the © Springer Nature Switzerland AG 2020 M. S. Bouhlel and S. Rovetta (Eds.): SETIT 2018, SIST 147, pp. 261–268, 2020. https://doi.org/10.1007/978-3-030-21009-0_25