Metallic structures for photodetector application

• Main Author: Lam, Zhao Meng
• Other Authors: Zhang Dao Hua
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2020
• Subjects: Engineering::Electrical and electronic engineering
• Online Access: https://hdl.handle.net/10356/136840
• Institution: Nanyang Technological University

For this project we are going to conduct a comprehensive numerical study of localized surface plasmon based split ring resonator with the purpose of enhancing absorption in mid-IR photodetector. We will investigate the resonance properties of U-shaped SRR structure based on different incident polarizations with varying geometrical parameters such as the SRR size, width, thickness, and substrate refractive index. The resonance characteristics of an SRR will be understood from the perspective of LC-circuit where the SRR gaps constitutes the capacitance and the SRR area (and circumferential length) constitutes an inductance. The dependence of the spectral mode position on the SRR size confirms the validity of the interpretation based on LC-circuit analogy. The variation of width and thickness can be understood to be related to the resistance element in the RLC-circuit analogy, where increasing thickness (or width) translates to a decrease in non-radiative ohmic resistance leading to higher radiative efficiency and shorter resonance wavelength. We will investigate the role of substrate refractive index in the resonance characteristics, and again confirm the validity of the LC-circuit analogy, particularly in its λ_0∝√(ϵ_C ) dependence. Finally, we will apply this insight into designing U-SRR for mid-IR photodetection on InAsSb substrate. The SRR resonance modes are first characterized in the constant dielectric refractive index for more clarity, which will then be followed by implementing a more realistic refractive index of InAsSb based on Adachi. It will be shown that for 3.5µm absorption in InAs0.91Sb0.09 the matching SRR size would be in 250-300nm range for x-polarization (based on m0 mode) and 450-500nm range for y-polarization (based on e0 mode). However, closer investigation on the effective loss with U-SRR will reveal that the absorption enhancement only occurs for x-polarized m0 mode. This is mainly attributed due to the strong radiation of the y-polarized e0 mode which significantly reflect the light before being absorbed in the detection region.