We demonstrate an improvement in efficiency of optically thin GaAs solar cells decorated with size-controlled Ag nanoparticles fabricated by masked deposition through anodic aluminum oxide templates. The strong scattering by the interacting surface plasmons in densely formed high aspect-ratio nanoparticles effectively increases the optical path of the incident light in the absorber layers resulting in an 8% increase in the short circuit current density of the cell. The nanoparticle array sheet conductivity also reduces the cell surface sheet resistance evidenced by an improved fill factor. This dual function of plasmonic nanoparticles has potential to enable thinner photovoltaic layers in solar cells.

Monolithic integration of III-V compound semiconductors on silicon is highly sought after for high-speed, low-power-consumption silicon photonics and low-cost, light-weight photovoltaics. Here we present a GaAs/Si direct fusion bonding technique to provide highly conductive and transparent heterojunctions by heterointerfacial band engineering in relation to doping concentrations. Metal- and oxide-free GaAs/Si ohmic heterojunctions have been formed at 300°C; sufficiently low to inhibit active material degradation. We have demonstrated 1.3 μm InAs/GaAs quantum dot lasers on Si substrates with the lowest threshold current density of any laser on Si to date, and AlGaAs/Si dual-junction solar cells, by p-GaAs/p-Si and p-GaAs/n-Si bonding, respectively. Our direct semiconductor bonding technique opens up a new pathway for realizing ultrahigh efficiency multijunction solar cells with ideal bandgap combinations that are free from lattice-match restrictions required in conventional heteroepitaxy, as well as enabling the creation of novel high performance and practical optoelectronic devices by III-V/Si hybrid integration.

We report the fabrication of InAs/GaAs quantum dot solar cells (QDSCs) with enhanced photocurrent and no degradation in open circuit voltage (VOC) compared to a solar cell grown without QDs and composed solely of wetting layers. Notably, the achievement of such high VOC does not require electronic coupling. We report QDSCs with a light absorption range extended up to 1.3 μm and evidence a trade-off between VOC and QD ground-state energy. These results are of major significance to the design of high efficiency QDSCs.

Metal nanoparticles and nanoshells consisting of metal shells and dielectric cores are known to significantly enhance incident electromagnetic fields around themselves due to surface plasmons. The field enhancement factors were calculated for spherical metal nanoparticles and nanoshells in the quasistatic limit using empirical wavelength-dependent dielectric constants. Dependence of the field enhancement factor on various parameters, such as wavelength, distance from the nanoparticle/nanoshell, metal element, dielectric core material, surrounding medium, and diameter ratio between the core and the shell, was investigated. Interestingly the peak field enhancement factor becomes largest with core-to-shell diameter ratio at ∼0.9 for any combination of noble metal shell and dielectric core. As a consequence of the parameter optimization, it was found that an Ag nanoshell with a Teflon core with a core/shell diameter ratio of 0.88 exhibits a peak field enhancement factor of 1400 in its vicinity in water.

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