Enhancement of spontaneous recombination rate in a quantum well by resonant surface plasmon coupling

Abstract

Using time-resolved photoluminescence measurements, the recombination rate in an In0.18Ga0.82N/GaN quantum well (QW) is shown to be greatly enhanced when spontaneous emission is resonantly coupled to a silver surface plasmon. The rate of enhanced spontaneous emission into the surface plasmon was as much as 92 times faster than normal QW spontaneous emission. A calculation, based on Fermi's golden rule, reveals the enhancement is very sensitive to silver thickness and indicates even greater enhancements are possible for QWs placed closer to the surface metal coating.The spontaneous emission (SE) decay constant τ for radiating dipoles at r e is given by Fermi's golden rulewhere ρ(hω) is the photon density of states (DOS) and f | d · E( r e )|i is the dipole emission matrix element. As pointed out by Purcell, SE may be enhanced by altering the photon DOS 1 . For example, the ratio of enhanced to free space emission (the Purcell factor F ) has been measured as large as 5 in an atomic system by placing the radiating atoms in a high Q, low volume cavity 2,3 . A Purcell factor of up to 6 has been observed from quantum well (QW) and quantum dot emitters in vertical cavity surface emitting laser structures, while an enhancement of 15 has been observed from quantum dots in a microdisk cavity 4,5 . Photonic crystals and distributed Bragg gratings have also been used to enhance the SE rate by as much as a factor of 4.5 6,7,8 . Such enhanced SE rates, achieved by increasing the photonic DOS in a small cavity, permit lower threshold, higher modulation frequency lasers as well as more efficient light emitting diodes.The SE rate can also be modified when semiconductor or dye emitters are coupled to a surface plasmon (SP) of a metallic film 9,10,11,12 . A single QW can experience strong quantum electrodynamic coupling to a SP mode if placed within the SP fringing field penetration depth. An electron-hole pair in the QW recombines and emits a photon into a SP mode instead of into free space. The degree of SE rate modification for a given wavelength depends on the SP DOS at that wavelength. The strongest enhancement occurs near the asymptotic limit of the SP dispersion branch, the SP "resonance" energy E sp , where the SP DOS is very high. Non-resonant, SPmediated SE enhancements as large as 6 have been observed from GaAs QWs near thin Ag films 9 . Even greater enhancements are possible for wide bandgap semiconductors whose emission wavelength is coincident with E sp . In this report, time-resolved photoluminescence (TRPL) measurements of a partially silver-coated InGaN/GaN QW directly demonstrate the SP-mediated resonant enhancement of the SE rate for the first time in a semiconductor QW. An InGaN/GaN QW was used in these experiments, grown by metal-organic chemical vapor deposition (MOCVD) on sapphire substrate 13 . Over a 1.5 µm Si-doped GaN buffer layer was grown a 28 nm In 0.04 Ga 0.96 N reference layer, a 6 nm GaN layer, and the 3 nm In 0.18 Ga 0.82 N QW as shown in Fig. 1. Above the QW was a 12 nm Si-doped GaN cap layer, pl...

Optical antenna enhanced spontaneous emission

“…This measure of spontaneous emission rate is complementary to lifetime measurements. Lifetime can be influenced by emitters coupling to surface plasmons or optical cavities, which may not radiate, the energy still being lost as heat (21,27), whereas the intensity method demands a knowledge of relative pump efficiency, relative emission pattern, and possible difference in internal quantum efficiency near the antenna.…”

“…Metal structures have also been used to enhance the spontaneous emission rate, such as by coupling excited material to flat surface plasmon waves (21)(22)(23)(24)(25)(26)(27)(28). Flat metal surfaces are far from ideal antennas, resulting in low radiation efficiencies and large ohmic losses.…”

Surface plasmon enhanced spontaneous emission rate of InGaN∕GaN quantum wells probed by time-resolved photoluminescence spectroscopy

“…3 Recently, we have reported a method for enhancing the light emission efficiency from InGaN QWs by controlling the energy transfer between QW emitters and surface plasmons ͑SPs͒. 4 The idea of SP enhanced light emission was previously described [5][6][7][8][9][10][11][12][13][14][15] and efficient SPenhanced visible light emission has been demonstrated. 4 Moreover, the enhancement of an emission rate is also very important for the development of communication technology and optical computing.…”

Comparison of electrostatic and localized plasmon induced light enhancement in hybrid InGaN/GaN quantum wells

“…5(a)). This is a signature of plasmonic coupling 6,7 and is caused by the enhancement of the spontaneous emission rate. The Au filled InGaN/GaN quantum wells, on the other hand, show a longer recombination time compared to the reference sample.…”

“…[4][5][6] Despite the large increase in the spontaneous emission rate, however, surface plasmon mediated enhancement of light emission is limited by Joule heating and non-radiative recombination at the metal-semiconductor interface. [7][8][9] One possible way to reduce Joule heating is to utilize localized surface plasmons (LSPs) using metal nanoparticles (NPs) 5,7 The presence of metal NPs on or embedded within light emitters also facilitates the tunability of the localized plasmon frequency compared to long range surface plasmon frequency, which is usually fixed in case of thin film. In case of the thin films, the dielectric constant of the metal and the semiconductor surface characterizes the LSP energy and thereby the upper limit of the photons energy of the emitter that can be resonantly coupled with the plasmons.…”