Edward Gonzales

Tailoring Directional Scattering through Magnetic and Electric Resonances in Subwavelength Silicon Nanodisks

Interference of optically induced electric and magnetic modes in high-index all-dielectric nanoparticles offers unique opportunities for tailoring directional scattering and engineering the flow of light. In this article we demonstrate theoretically and experimentally that the interference of electric and magnetic optically induced modes in individual subwavelength silicon nanodisks can lead to the suppression of resonant backscattering and to enhanced resonant forward scattering of light. To this end we spectrally tune the nanodisks fundamental electric and magnetic resonances with respect to each other by a variation of the nanodisk aspect ratio. This ability to tune two modes of different character within the same nanoparticle provides direct control over their interference, and, in consequence, allows for engineering the particles resonant and off-resonant scattering patterns. Most importantly, measured and numerically calculated transmittance spectra reveal that backward scattering can be suppressed and forward scattering can be enhanced at resonance for the particular case of overlapping electric and magnetic resonances. Our experimental results are in good agreement with calculations based on the discrete dipole approach as well as finite-integral frequency-domain simulations. Furthermore, we show useful applications of silicon nanodisks with tailored resonances as optical nanoantennas with strong unidirectional emission from a dipole source.

Active tuning of mid-infrared metamaterials by electrical control of carrier densities

We demonstrate electrically-controlled active tuning of mid-infrared metamaterial resonances using depletion-type devices. The depletion width in an n-doped GaAs epilayer changes with an electric bias, inducing a change of the permittivity of the substrate and leading to frequency tuning of the resonance. We first present our detailed theoretical analysis and then explain experimental data of bias-dependent metamaterial transmission spectra. This electrical tuning is generally applicable to a variety of infrared metamaterials and plasmonic structures, which can find novel applications in chip-scale active infrared devices.

Realization of tellurium-based all dielectric optical metamaterials using a multi-cycle deposition-etch process

Tellurium (Te) dielectric resonator metamaterials for thermal infrared applications were fabricated using a multi-cycle deposition-etch process that circumvents pinch-off issues during deposition. Deposition and etching of Te were studied in detail. Metamaterial samples with varying resonator dimensions were fabricated using this technique. All the samples showed two transmission minima corresponding to magnetic and electric dipole resonances. Longer resonant wavelengths were observed as the resonator dimension was increased. Observation of spectral overlap between magnetic and electric resonances gives us the potential opportunity to realize a negative refractive index material.

Electrically-controlled thermal infrared metamaterial devices

We demonstrate electrically-controlled thermal mid-infrared metamaterials using depletion-type semiconductor devices. This electrical tuning can find novel applications in chip-scale active infrared devices.

Merging magnetic and electric resonances for all-dielectric nanoantenna arrays

We spectrally overlap the magnetic and electric resonances in all-dielectric silicon nanodisk arrays by tuning the disk aspect ratio. This offers new opportunities for functional metasurfaces and conceptually new all-dielectric unidirectional nanoantennas.

Realization of Tellurium-based all dielectric optical metamaterials using a multi-cycle deposition-etch process

Tellurium dielectric resonator metamaterials were fabricated using a newly developed multi-cycle deposition-etch process. Deposition and etching of Tellurium were studied in detail. All the samples showed two transmission minima corresponding to magnetic and electric dipole resonances.

Record breaking solar cells : ZnxCd(1-x)Te graded bandgap nanoarrays.

CdTe is the leading material for thin-film solar cells due to ease of processing and reduced cost. However, low conversion efficiencies due to defects in the material are still a problem in these devices. We propose implementing micro and nano-enabled pseudomorphic growth of ZnCdTe to dramatically increase the efficiency of CdTe solar cells. Simulations predict that defect-free films are possible in graded ZnCdTe nanoislands below 90 nm as well as 24 % efficient solar cells with the use of ZnCdTe grading. Selective growth of CdTe showed single grains when the island sizes decreased below 300 nm. The simulation and experimental results demonstrate for the first time the ability to use nanopatterned substrates to enhance uniformity and efficiency in CdTe thin film solar cells. More than 20 reports, presentations, and papers were produced as part of this work and the results from this project enabled UTEP and Sandia to secure to grants.