Temperature dependence of exciton-surface plasmon polariton coupling in Ag, Au, and Al films on InxGa1−xN/GaN quantum wells studied with time-resolved cathodoluminescence

Abstract

The optical properties and coupling of excitons to surface plasmon polaritons (SPPs) in Ag, Au, and Al-coated In x Ga 1Àx N/GaN multiple and single quantum wells (SQWs) were probed with timeresolved cathodoluminescence. Excitons were generated in the metal coated SQWs by injecting a pulsed high-energy electron beam through the thin metal films. The Purcell enhancement factor (F p) was obtained by direct measurement of changes in the temperature-dependent radiative lifetime caused by the SQW exciton-SPP coupling. Three chosen plasmonic metals of Al, Ag, and Au facilitate an interesting comparison of the exciton-SPP coupling for energy ranges in which the SP energy is greater than, approximately equal to, and less than the excitonic transition energy for the InGaN/GaN QW emitter. A modeling of the temperature dependence of the Purcell enhancement factor, F p , included the effects of ohmic losses of the metals and changes in the dielectric properties due to the temperature dependence of (i) the intraband behavior in the Drude model and (ii) the interband critical point transition energies which involve the d-bands of Au and Ag. We show that an inclusion of both intraband and interband effects is essential when calculating the x vs k SPP dispersion relation, plasmon density of states (DOS), and the dependence of F p on frequency and temperature. Moreover, the "back bending" in the SPP dispersion relation when including ohmic losses can cause a finite DOS above x sp and lead to a measurable F p in a limited energy range above x sp , which can potentially be exploited in plasmonic devices utilizing Ag and Au.

Enhancement in the excitonic spontaneous emission rates for Si nanocrystal multi-layers covered with thin films of Au, Ag, and Al

“…Three chosen plasmonic metal films of Ag, Au, and Al facilitate an interesting comparison of the exciton-SPP coupling and enhancement of the SER for varying relative differences in the surface plasmon frequency, ω sp , and the SiNC emission energy of ∼1.88 eV. In calculating the SER enhancement for Ag, Au, and Al films on the SiNC multilayer structure, we employ a model that we have recently used for the calculation of the temperature dependence of the Purcell enhancement factor, F p , for the same metal films on InGaN/ GaN quantum wells [22]. The model includes the effects of ohmic losses of the metals and changes in the dielectric properties due to the temperature dependence of (i) the intraband behavior in the Drude model and (ii) the interband critical point transition energies which involve the d-bands of Au and Ag.…”

“…We have used a standard two-dimensional (2D) SPP energy dispersion relation model for a flat metal film covering a dielectric material layer (i.e., SiO 2 in our case) which will provide a reasonable model from which the ω versus k dispersion relations can be calculated for the Au-, Ag-, and Alcovered SiO 2 /SiNC multi-layer structures [18,19,22,37,45]. From the solution of Maxwell's equations with a matching of boundary conditions at the interfaces of the vacuum/metal/SiO 2 system, we have calculated the ω versus k dispersion relations for various temperatures between 55 and 300 K which also include the temperature-dependent losses for Ag, Al, and Au films possessing thickness (t) of 30 nm on SiO 2 .…”

“…The temperature dependence of the Drude term, ε D (ω, T), for nearly free valence electrons, describes the intraband behavior. We have previously utilized a model for the temperature dependence of ε D (ω, T), which includes the temperature dependence of plasma frequency, electron-electron collision rate, and electron-phonon scattering rate [22]. The interband contribution is typically modeled using one or more Lorentzian oscillator terms [49,51,52].…”

“…Due to the opacity of the metal with respect to light/laser excitation from the top surface, time-resolved cathodoluminescence (CL) is shown to be a particularly useful probe for metal-coated QWs and Si nanostructures [22,34,35] in that the high-energy e-beam can easily penetrate the metal film and create excess e-h pairs in the semiconductor NCs. In this paper, we investigate the temperature dependence of F p for Ag, Au, and Al films deposited on multi-layers of SiNCs by performing time-resolved CL measurements to measure changes in the e-h recombination lifetime caused by the metal films.…”

“…In this paper, we investigate the temperature dependence of F p for Ag, Au, and Al films deposited on multi-layers of SiNCs by performing time-resolved CL measurements to measure changes in the e-h recombination lifetime caused by the metal films. In order to correctly model the temperature dependence of F p , the inclusion of the effects of ohmic losses of the metals and changes in the critical point transition energies (i.e., changes in the metal band gaps) as a function of temperature is essential when calculating the ω versus k SPP dispersion relation, plasmon DOS, and the dependence of F p on frequency and temperature [22]. Moreover, the 'back bending', which is due to ohmic losses in the SPP dispersion [22,[36][37][38][39], can cause a finite DOS above ω sp and lead to a measurable F p in a limited energy range above ω sp , which can potentially be exploited in plasmonic devices utilizing Ag and Au with even potentially adjusting the ohmic losses according to the various methods of film preparation and deposition.…”