Surface plasmons provide a pathway to efficiently absorb and confine light in metallic nanostructures, thereby bridging photonics to the nano scale. The decay of surface plasmons generates energetic ‘hot’ carriers, which can drive chemical reactions or be injected into semiconductors for nano-scale photochemical or photovoltaic energy conversion. Novel plasmonic hot carrier devices and architectures continue to be demonstrated, but the complexity of the underlying processes make a complete microscopic understanding of all the mechanisms and design considerations for such devices extremely challenging. Here,we review the theoretical and computational efforts to understand and model plasmonic hot carrier devices. We split the problem into three steps: hot carrier generation, transport and collection, and review theoretical approaches with the appropriate level of detail for each step along with their predictions. We identify the key advances necessary to complete the microscopic mechanistic picture and facilitate the design of the next generation of devices and materials for plasmonic energy conversion.
Quantum plasmonics is an exciting subbranch of nanoplasmonics where the laws of quantum theory are used to describe light–matter interactions on the nanoscale. Plasmonic materials allow extreme subdiffraction confinement of (quantum or classical) light to regions so small that the quantization of both light and matter may be necessary for an accurate description. State-of-the-art experiments now allow us to probe these regimes and push existing theories to the limits which opens up the possibilities of exploring the nature of many-body collective oscillations as well as developing new plasmonic devices, which use the particle quality of light and the wave quality of matter, and have a wealth of potential applications in sensing, lasing, and quantum computing. This merging of fundamental condensed matter theory with application-rich electromagnetism (and a splash of quantum optics thrown in) gives rise to a fascinating area of modern physics that is still very much in its infancy. In this review, we discuss and compare the key models and experiments used to explore how the quantum nature of electrons impacts plasmonics in the context of quantum size corrections of localized plasmons and quantum tunneling between nanoparticle dimers. We also look at some of the remarkable experiments that are revealing the quantum nature of surface plasmon polaritons.
Vladimir Bochenkov, Jeremy Baumberg, Mikhail Noginov, Felix Benz, Hasan Aldewachi, Silvan Schmid, Viktor Podolskiy, Javier Aizpurua, Kaiqiang Lin, Thomas Ebbesen, Alexei A Kornyshev, James Hutchison, Katarzyna Matczyszyn, Samir Kumar, Bart de Nijs, Francisco Rodriguez Fortuno, James T. Hugall, Pablo de Roque, Niek van Hulst, Santhosh Kotni, Olivier Martin, F. Javier Garcia de Abajo, Michael Flatte, Andrew Mount, Martin Moskovits, Pavel Ginzburg, David Zueco, Anatoly Zayats, Sang-Hyun Oh, Yu Chen, David Richards, Alessandro Belardini, and Prineha Narang. 2015. “Applications of plasmonics: general discussion.” Faraday Discuss., 178, Pp. 435-466. Publisher's Version
The search for new direct bandgap, earth-abundant semiconductors for efficient, high-quality optoelectronic devices, as well as photovoltaic and photocatalytic energy conversion has attracted considerable interest. One methodology for the search is to study ternary and multiternary semiconductors with more elements and more flexible properties. Cation mutation such as binary → ternary → quaternary for ZnS → CuGaS2 → Cu2ZnSnS4 and ZnO → LiGaO2 → Li2ZnGeO4 led to a series of new quaternary chalcogenide and oxide semiconductors with wide applications. Similarly, starting with GaN, ternary nitrides such as ZnSnN2 and ZnGeN2 have been designed and synthesized recently. However, quaternary nitride semiconductors have never been reported either theoretically or experimentally. Through a combination of the Materials Genome database with the first-principles calculations, we designed a series of quaternary nitride compounds I–III–Ge2N4 (I = Cu, Ag, Li, Na, K; III = Al, Ga, In) following the GaN → ZnGeN2 → I–III–Ge2N4mutation. Akin to Li2ZnGeO4, these quaternary nitrides crystallize in a wurtzite-derived structure as their ground state. The thermodynamic stability analysis shows that while most of them are not stable with respect to phase separation, there are two key exceptions (i.e., LiAlGe2N4 and LiGaGe2N4), which are stable and can be synthesized without any secondary phases. Interestingly, they are both lattice-matched to GaN and ZnO, and their band gaps are direct and larger than that of GaN, 4.36 and 3.74 eV, respectively. They have valence band edges as low as ZnO and conduction band edges as high as GaN, thereby combining the best of GaN and ZnO in a single material. We predict that flexible and efficient band structure engineering can be achieved through forming GaN/LiAlGe2N4/LiGaGe2N4 heterostructures, which have tremendous potential for ultraviolet optoelectronics.
ZnSn1‐xGexN2 direct bandgap semiconductor alloys, with a crystal structure and electronic structure similar to InGaN, are earth‐abundant alternatives for efficient, high‐quality optoelectronic devices and solar‐energy conversion. The bandgap is tunable almost monotonically from 2 eV (ZnSnN2) to 3.1 eV (ZnGeN2) by control of the Sn/Ge ratio.
First‐principles calculations show that ZnSnN2 has a very small formation enthalpy, and the donor defects such as SnZn antisites and ON impurities have high concentration, making the material degenerately n‐type, which explains the observed high electron concentration. ZnSnN2 can be regarded as a new material that combines a metal‐like conductivity with an optical bandgap around 2 eV.
Collection of hot electrons generated by the efficient absorption of light in metallic nanostructures, in contact with semiconductor substrates can provide a basis for the construction of solar energy-conversion devices. Herein, we evaluate theoretically the energy-conversion efficiency of systems that rely on internal photoemission processes at metal-semiconductor Schottky-barrier diodes. In this theory, the current-voltage characteristics are given by the internal photoemission yield as well as by the thermionic dark current over a varied-energy barrier height. The Fowler model, in all cases, predicts solar energy-conversion efficiencies of <1% for such systems. However, relaxation of the assumptions regarding constraints on the escape cone and momentum conservation at the interface yields solar energy-conversion efficiencies as high as 1%–10%, under some assumed (albeit optimistic) operating conditions. Under these conditions, the energy-conversion efficiency is mainly limited by the thermionic dark current, the distribution of hot electron energies, and hot-electron momentum considerations.
Decay of surface plasmons to hot carriers finds a wide variety of applications in energy conversion, photocatalysis and photodetection. However, a detailed theoretical description of plasmonic hot-carrier generation in real materials has remained incomplete. Here we report predictions for the prompt distributions of excited ‘hot’ electrons and holes generated by plasmon decay, before inelastic relaxation, using a quantized plasmon model with detailed electronic structure. We find that carrier energy distributions are sensitive to the electronic band structure of the metal: gold and copper produce holes hotter than electrons by 1–2 eV, while silver and aluminium distribute energies more equitably between electrons and holes. Momentum-direction distributions for hot carriers are anisotropic, dominated by the plasmon polarization for aluminium and by the crystal orientation for noble metals. We show that in thin metallic films intraband transitions can alter the carrier distributions, producing hotter electrons in gold, but interband transitions remain dominant.