Metallic Nanodroplet Induced Coulomb Catalysis for Off-Resonant Plasmonic Enhancement of Photoemission in Semiconductors

Abstract

The enhancement of light from semiconductors due to surface plasmons coupled resonantly to its emission is limited because of dissipation in the metal and is also restricted by the dielectric characteristics and homogeneity of the metal–semiconductor interface. We report a new mechanism based on electrostatic interactions of carriers and their image charges in metals to generate more photons from optical sources at frequencies that are off-resonant to the localized plasmon frequency. Coulomb catalysis of carrier accumulation resulting from the inhomogeneity of metal nanodroplets on a semiconductor’s surface can result in an enhancement of light that is nondissipative and does not require resonant coupling of plasmons to the emission wavelength. The enhancement occurs because of an increase in the ratio of radiative to nonradiative recombination in the vicinity of metal nanoparticles. It is equally effective with any type of metal and enhances radiation at any frequency, a property that is of principal importance for the realization of widely tunable semiconductor emitters. This fundamental mechanism provides a new perspective for improving the efficiency of light emitters and controlling carrier concentration on the nanoscale. The structural characteristics of the hybrid metal–semiconductor emitters are studied using electron microscopy and atomic force microscopy. We demonstrate the electrostatic mechanism by studying steady-state and transient photoluminescence from two-dimensional semiconductors, such as GaAs/AlGAs quantum wells, and bulk semiconductors, such as ZnO thin films, emitting in the near-IR and UV wavelength regimes, respectively.

Competition Between Resonant Plasmonic Coupling and Electrostatic Interaction in Reduced Graphene Oxide Quantum Dots

“…The off-resonant interaction under appropriate conditions can also result in an enhancement of PL emission which has been observed in case of GaAs quantum wells in the presence of Ga nanoparticles26. Although under lower concentration of Au nanoparticles, there is no enhancement of the emission from rGO, on increasing the concentration of Au nanoparticles coupled to the rGO quantum dots, the light emission intensity can be significantly enhanced.…”

“…7b). This blue shift of the emission edge is due to the electrostatic Coulomb attraction induced by the formation of the image of the electrons and holes in the metal nanoparticles26. Figure (8) shows the electrostatic effects are prevalent when the radius of nanoparticles is less than 60 nanometers and the light is off-resonant compared to the localized plasmon energy.…”

Plasmonically-powered hot carrier induced modulation of light emission in a two-dimensional GaAs semiconductor quantum well

“…This modification in radiative recombination is relatively slow owing to the drift and diffusion process involved in the electrostatic attraction of the carriers to the nanoparticle. 30 The modified band-line up the quantum well due to the image charge effect is shown in the inset of Fig. 2c.…”

“…However, due to the carrier density increase around the metal nanoparticles due to the image-charge effect, the PL emission is enhanced about 25 fold. The PL emission is shifted to 1.557 eV owing to the electrostatic image charge effect 30 by virtue of the modified radiative recombination. This induces modification of the emitted light as illustrated in Fig.…”

“…However, being a relatively slower process than the plasmonically powered process, the electrostatic effect is usually dominated by plasmonic interaction under resonant conditions. It is plausible to harness the fast response of the localized surface plasmon (LSP) induced hot carriers to control light emission 30 with single metal nanoparticle plasmonic systems. However, extreme restrains must be exercised on the metal nanoparticle concentration.…”