Circular ring plasmonic optical antenna enhanced quantum dot infrared photodetectors

摘要

Antennas have played a significant role in transmitting and receiving electromagnetic waves in the spectral regimes of r.f., microwaves. and millimeter-wave, while optical antennas are the counterparts in the optical spectral regimes such as visible, Near-infrared (IR), and Mid-wavelength infrared (MWIR) and Long-wavelength infrared (LWIR). Optical antennas and their applications have been widely explored in the field of light sensing and emission properties' control. With the applicable optical antenna structures, localized surface plasmonic resonance (LSPR) modes can be excited in optical antennas. These optical antenna structures are referred to as plasmonic optical antennas (POAs). POAs can effectively modify the near-field electric-field (E-field) and current distributions. Moreover, they can enable efficient interaction with low-dimensional materials, such as quantum dot infrared photodetectors (QDIPs).;In this work. circular ring POAs have been developed, since they have shown great promises in light confinement and E-field enhancement in the near-infrared spectral region. First, surface current localization and enhancement scaling in metallic circular ring POA enhanced LWIR QDIPs are studied. The current distributions on the circular ring POAs with different ring widths are simulated under a plane wave incidence. The surface current density increases with reduced ring width, leading to surface current localization. LWIR QDIPs with different circular ring POAs were fabricated. POA induced photocurrent enhancement spectra were measured. A higher enhancement was obtained on the circular ring POA with a stronger surface current localization.;Secondly. antenna to antenna coupling (mutual coupling) has been analyzed in a concentric circular ring POA array. A simple lumped coupled circuit (LCC) model was applied in this research to analyze the POA array, and the current distributions of the array elements and their mutual couplings are investigated. CST's Microwave Studio was used for numerical simulation and the simulation results were compared with what obtained from the model and the comparison showed great consistency. The mutual couplings phenomena were found among the POA array to not just exist in between the adjacent antenna elements, but also on 2nd nearest or farther antenna elements.;Finally, this research presented a concentric circular ring and nanodisk POA enhanced multispectral QDIP structure, which was designed to have plasmonic resonances in both MWIR and LWIR spectral regimes. It was found that the E-fields locate in the circular ring region at longer wavelengths. while at shorter wavelengths the E-fields locates closer to the nanodisk region. The simulated spectrum showed that the enhancement regions of this structure are in the range of 3-9 microm and 9.6-11 microm.