20 June 2022

Séminaire / Seminar : « Silicon-based infrared photodetectors functionalized by plasmonic structures » by Dr. Shun Yasunaga (Tokyo University, Mita Lab)

Dr. Shun Yasunaga (Tokyo University, Mita Lab)

Title : Silicon-based infrared photodetectors functionalized by plasmonic structures

Abstract :
Silicon has been considered unsuitable for infrared photodetection over 1.1 µm in wavelength, where silicon becomes transparent as the energy of photon decreases to below the bandgap. Using plasmonic structure (i.e., subwavelength metallic structure), however, we can not only cause light-matter interaction on silicon-based devices but also add function to it such as wavelength selectivity. I will talk on two realizations of such optical devices. The first one is a nanohole near-infrared photodetector that realizes high responsivity at 1.1 µm to 1.8 µm in wavelength. Copper nanoantennas fabricated using a nanohole array on n-type silicon produce enhanced photocurrent as hot electrons
efficiently get over the energy barrier at the metal/semiconductor interface. Secondly, I talk about a bolometer that has an aluminum-coated plasmonic grating. When a narrow trench is used as the periodic structure, the responsivity sharply changes by the wavelength, resulting in a high contrast between the lowest and the highest responsivity. Such bolometer is an ideal component of the miniature spectrometers that numerically reconstructs the spectrum using the
inverse problem approach (called « reconstructive spectroscopy »). Through these devices, I introduce how we can obtain new device characteristics by using plasmonic structures.Bio :
Shun Yasunaga is a post-doc fellow at the University of Tokyo, Japan. His research interest has been in micro electro-mechanical systems (MEMS) and plasmonics to produce functional optical devices, especially in the infrared regime. He majored in mechanical engineering and information science and has just obtained PhD degree last March by a thesis on mid-infrared plasmonic photodetectors for reconstructive spectroscopy. He now continues research under Prof. Yoshio Mita, the leading researcher in the field of MEMS.