Electromagnetic Energy Distribution in Resonant Quasi Porous Silicon Nanostructures

Odebo Lank N., Kall M. and Antosiewicz T.J.

ACS Photonics

6(7), 2019, 1706-1714, 10.1021/acsphotonics.9b00348

Geometric resonances in high refractive index dielectric nanoantennas enhance the local density of optical states, increasing the decay rate of electric and magnetic dipolar emitters. Due to low losses, dielectric antennas exhibit less quenching than their plasmonic counterparts. However, enhanced fields associated with these resonances, in contrast to plasmonic ones, are confined to the particle interior, complicating efficient coupling strategies. Previous research has focused on emitters either placed next to dielectric antennas or incorporated into them during fabrication. Making the nanoantenna porous enables access to the internal fields while being flexible during fabrication. Herein, a model porous silicon antenna is analyzed, and the available electromagnetic energy within it is investigated. A porosity of 30% achieves an optimal balance between antenna quality and energy available in the pores. To minimize disturbance to the optical modes, the pores should be no larger than 5% of the size of the antenna. Moreover, the magnetic dipole resonance of these structures is remarkably robust to perturbations and is thus a promising target for applications due to its tolerance to fabrication error. Calculations show that nonradiative decay is important for electric emitters despite relatively low material losses, while magnetic dipole decay rate enhancement is completely dominated by radiative yield.