Fabrice Pardo

Dark current investigation in thin P-i-N InGaAs photodiodes for nano-resonators

We investigated the dark current components of thin planar InGaAs photodiodes grown by metalorganic vapor-phase epitaxy for optical nano-resonators. Owing to their high electric field enhancement, nano-resonators make it possible to substantially reduce the thickness of the active region to about 100u2009nm all the while maintaining high quantum efficiency. In the present study, to cover a broad spectral band, we combined several resonance peaks induced by guided-mode resonances in a given spectral range. This type of geometry allowed us to introduce InAlAs at the edge of a thin InGaAs active region in order to drastically reduce both the diffusion current and the generation/recombination current. We found that, in such devices, tunneling dark current components increase as the thickness of the active layer is reduced and dominate the reverse dark current. By optimizing the epitaxial stack, while keeping its total thickness constant (the optical properties of the nano-resonator remained unchanged), we showed ...

Investigating the optical properties of nanogap optical antennas

We investigate the optical properties of nanogap MIM nanoantennas with a 2.1 nm thick gap. These plasmonic nanoantennas consist of a gold film, an insulating layer deposited by Atomic Layer Deposition, and a periodically structured gold layer. MIM nanoantennas are characterized by a tunable spectral response and a high field confinement within the nanogap. Nanometric gaps enable high coupling between the plasmons of the top and bottom metal surfaces. We demonstrated an excellent agreement between optical measurements and classical electromagnetic simulations. In particular, we observed a fluctuation in the gap thickness of 0.2 nm.

Limited-size guided-mode resonance filters under focused beams

We investigate the impact of focused beams on metal-dielectric guided-mode-resonance filters. Under a planewave illumination, these filters show a resonant transmission at an easily tunable wavelength and a good angular acceptance. Although guided-mode resonance is involved, calculations show that under a focused beam the lateral extension of the electromagnetic field inside the waveguide is limited to the width of the beam. We investigate evolution of this lateral extension and the resonant transmission with the size of the beam, as well as the impact of a tilted beam. Guided-mode-resonance filtering under a focused beam is illustrated through the example of a Cassegrain microscope lens. A process for the fabrication of simple metal-dielectric filters is also presented.

Optical Nanoantennas For High-Efficient Ultra-Thin Solar Cells

We propose new concepts for light trapping in ultra-thin solar cells. It is shown that optical nanoantennas can lead to broadband absorption in 30nnm-thick GaAs solar cells, with 14.5% energy conversion efficiency.