Planar metal-oxide-metal structures can serve as photodetectors that do not rely on the usual electron-hole pair generation in a semiconductor. Instead, absorbed light in one of the metals can produce a current of hot electrons when the incident photon energy exceeds the oxide barrier energy. Despite the desirable traits of convenient fabrication and room-temperature operation at zero bias of this type of device, the low power conversion efficiency has limited its use. Here, we demonstrate the benefits of reshaping one of the metallic contacts into a plasmonic stripe antenna. We use measurements of the voltage-dependence, spectral-dependence, stripe-width dependence, and polarization-dependence of the photocurrent to show that surface plasmon excitations can result in a favorable redistribution in the electric fields in the stripe that enhances the photocurrent. We also provide a theoretical model that quantifies the spectral photocurrent in terms of the electrical and optical properties of the junction. This model provides an accurate estimate of the bias dependence of the external quantum efficiency of different devices and shows that both the spatial and vectorial properties of the electric field distribution are important to its operation.

The success of semiconductor electronics is built on the creation of compact, low-power switching elements that offer routing, logic, and memory functions. The availability of nanoscale optical switches could have a similarly transformative impact on the development of dynamic and programmable metasurfaces, optical neural networks, and quantum information processing. Phase change materials are uniquely suited to enable their creation as they offer high-speed electrical switching between amorphous and crystalline states with notably different optical properties. Their high refractive index has also been harnessed to fashion them into compact optical antennas. Here, we take the next important step by realizing electrically-switchable phase change antennas and metasurfaces that offer strong, reversible, non-volatile, multi-phase switching and spectral tuning of light scattering in the visible and near-infrared spectral ranges. Their successful implementation relies on a careful joint thermal and optical optimization of the antenna elements that comprise an Ag strip that simultaneously serves as a plasmonic resonator and a miniature heating stage.

Bulk and thin films of III-VI and I-III-VI semiconductors such as In 2 Se 3 (IS), 1 CuInSe 2 (CIS) 2 and CuGaSe 2 3 have been actively studied for photovoltaic applications. Among them, polycrystalline thin films of CuIn x Ga 1-x Se 2 (CIGS) have been demonstrated to have a high-power efficiency of 19.2%, 4 which even outperforms the best single crystalline devices. 5 This extraordinary performance was proposed to be caused by a hole energy barrier at grain boundaries for preventing electron-hole recombination, 6,7 although this hypothesis is still under question. 8 In addition, the high efficiency is also attributed to the formation of random p-n junctions distributed in compositionally inhomogeneous polycrystalline thin films. 9 Nanowire (NW) morphology of I-III-VI chalcopyrite materials can provide a well-defined nanoscale domain with clearly identifiable "grain boundaries" for studying these effects. Aligned NWs with a controllable composition modulation can afford ordered p-n junctions and continuous charge carrier transport pathways without deadends, which is an advantage over the random p-n junctions. Therefore, NW solar cells 10 might provide an even higher efficiency. The promise will not be fulfilled without a method for fabricating the required NW structures. Herein, we report the synthesis of IS and CIS single crystalline NWs via a Au-catalyzed vapor-liquid-solid (VLS) growth. We demonstrate the temperature-induced reversible superlattice transformation in IS NWs. We also show that the crystal structure of CIS NWs has dependence on Cu concentration.A solvothermal method was used previously for producing CIS nanowiskers and nanoparticles although their morphology and crystallinity are ill-defined. 11 Solution colloidal synthesis was used to produce AgInSe 2 nanorods and nanoparticles with small aspect ratios less than 5. 12 We exploit a VLS growth [13][14][15] because this method has been shown to be among the most powerful ones for predictably synthesizing single-crystalline NW structures with a size, position, and orientation control.The synthesis of IS and CIS NWs has been carried out in a similar way as that in our previous studies 16 (Supporting Information). In a tube furnace, a carrier gas transports the vapor of R-phase IS or chalcopyrite-type CIS downstream. Gold colloids dispersed on Si substrates were used as VLS catalysts. Typical synthesis conditions are pressure ) 50 Torr, temperature ) 700 °C, time ) 5 h, and gas flow ) 120 sccm. To controllably adjust the Cu