ABSTRACT
By virtue of their distinctive electronic properties (including linear energy dispersion, large velocity, and potentially ultra-high mobility even at room temperature), charge carriers in single-layer graphene are uniquely suited to radiation mechanisms that so far have been the primary domain of electron beams in vacuum-based systems. Here, we consider the use of sinusoidally corrugated graphene sheets for the generation of THz light based on a fundamentally new cyclotron-like radiation process, which does not require the application of any external magnetic field. Instead, periodic angular motion under bias is simply produced by the graphene mechanical corrugation, combined with its two-dimensional nature which ensures that the carrier trajectories perfectly conform to the corrugation. Numerical simulations indicate that technologically significant output power levels can correspondingly be obtained at geometrically tunable THz frequencies. This mechanism (as well as similar electron-beam radiation processes such as the Smith-Purcell and Cherenkov effects in periodic nanostructures) may open the way for a new family of THz optoelectronic devices based on graphene, including solid-state 'free-electron' lasers potentially capable of room-temperature operation.
ABSTRACT
Diffractive arrays of silver nanocylinders are used to increase the radiative efficiency of InGaN/GaN quantum wells emitting at near-green wavelengths. Large enhancements in luminescence intensity (up to a factor of nearly 5) are measured when the array period exceeds the emission wavelength in the semiconductor material. The experimental results and related numerical simulations indicate that the underlying mechanism is a strong resonant coupling between the light-emitting excitons in the quantum wells and the plasmonic lattice resonances of the arrays. These excitations are particularly well suited to light-emission-efficiency enhancement, compared to localized surface plasmon resonances at similar wavelengths, due to their larger scattering efficiency and larger spatial extension across the sample area.
ABSTRACT
Two-dimensional arrays of silver nanocylinders fabricated by electron-beam lithography are used to demonstrate plasmon-enhanced near-green light emission from nitride semiconductor quantum wells. Several arrays with different nanoparticle dimensions are employed, designed to yield collective plasmonic resonances in the spectral vicinity of the emission wavelength and at the same time to provide efficient far-field scattering of the emitted surface plasmons. Large enhancements in peak photoluminescence intensity (up to a factor of over 3) are measured, accompanied by a substantial reduction in recombination lifetime indicative of increased internal quantum efficiency. Furthermore, the enhancement factors are found to exhibit a strong dependence on the nanoparticle dimensions, underscoring the importance of geometrical tuning for this application.
