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

Abstract

We observed a 32-fold increase in the spontaneous emission rate of InGaN/GaN quantum well ͑QW͒ at 440 nm by employing surface plasmons ͑SPs͒ probed by time-resolved photoluminescence spectroscopy. We explore this remarkable enhancement of the emission rates and intensities resulting from the efficient energy transfer from electron-hole pair recombination in the QW to electron vibrations of SPs at the metal-coated surface of the semiconductor heterostructure. This QW-SP coupling is expected to lead to a new class of super bright and high-speed light-emitting diodes ͑LEDs͒ that offer realistic alternatives to conventional fluorescent tubes. © 2005 American Institute of Physics. ͓DOI: 10.1063/1.2010602͔Currently, InGaN-GaN quantum well ͑QW͒ based lightemitting diodes ͑LEDs͒ have been developed and expected to eventually replace more traditional fluorescent tubes as illumination sources. 1,2 However, the emission efficacy of commercial white LEDs is still substantially lower than that of fluorescent tubes. 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 5-15 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. However, spontaneous emission rates of InGaN-GaN QWs are usually reduced by the carrier localization effect 16,17 and the quantum confinement Stark effect, 18,19 and very difficult to enhance. There are only a few reports on the enhancement of the emission rates by reducing the piezo-electric field 20 and making photonic crystal structure. 21 We believe that our developed SP coupling technique has the potential to enhance the spontaneous emission rate dramatically. 4 Since the density of states of SP mode is much larger, the QW-SP coupling rate should be very fast, and this new path of a recombination can increase the spontaneous emission rate. However, clear evidence for fast rate of QW-SP coupling has not so far been reported on the SP enhanced emission. We investigate the direct observation of SP coupled spontaneous emission rate by using the timeresolved photoluminescence ͑PL͒ measurements here. Moreover, we consider the mechanisms and dynamics of energy transfer and light extraction. This study should also be very useful for further optimization of the QW-SP coupling condition and for designing even more efficient device structures.InGaN-GaN QW wafers were grown on 0001 oriented sapphire substrates by metal-organic chemical vapor deposition ͑MOCVD͒. The grown structures consist of a GaN ͑4 m͒ buffer layer, an InGaN SQW ͑3 nm͒ followed by a GaN cap layer ͑10 nm͒. A 50 nm thick silver layer was then evaporated on top of the wafer surface. To perform timeresolved PL measurements, the frequency doubled output from a mode-locked Ti: Al 2 O 3 laser was used to...

Electronic modulation of infrared radiation in graphene plasmonic resonators

“…As thermal radiation is a form of spontaneous emission, the emission rate is increased by the presence of the plasmonic cavity, with the degree of rate enhancement dictated by the ratio between the Q factor and mode volume of the optical cavity (that is, the Purcell factor) 41 . This effect has been explored as a means of increasing LED switching rates by placing the semiconductor emitting layer within either a plasmonic or photonic cavity [42][43][44][45][46] . For the case of graphene plasmonic nanoresonators that have highly confined mode volumes, the Purcell factor has been shown to be extremely high, approaching 10 7 , and, thus, the modulation rate of thermal emission from our device could be exceedingly fast, beyond what has been demonstrated with plasmonically enhanced LEDs or lasers 47 .…”

Internal quantum efficiency enhancement of GaInN/GaN quantum-well structures using Ag nanoparticles

“…It has been demonstrated that k SP and k nrad follow similar trends as a function of temperature, and it is therefore reasonable to estimate k SP ∼ 0 at low temperatures and assume that IQE is approximately 100 % for the Ag NP coated samples. 27 We can then estimate the IQE of samples A-C the same way as the reference, and obtain 26.1 %, 26.4 % and 44.2 %, for samples A, B and C, respectively, with 756 W/cm 2 of excitation power density. Table I summarizes the IQE enhancement factors.…”

“…The emitted light from the QWs will see a modified interface when Ag NPs are included compared to a bare GaN-air interface, and this is expected to change the LEE. 27 In the following we will direct our attention to the IQE enhancement caused by the Ag NPs.…”

Time resolved photoluminescence spectroscopy of surface-plasmon-enhanced light emission from conjugate polymers

“…3͑a͒, a SP instead of a photon is produced by the molecular relaxation processes and thereby leads to an increase in the spontaneous recombination rate. This coupling mechanism resembles one presented for the inorganic semiconductor case, 16 although there is no buffer or cap layers as the conjugated polymer can be placed directly on the metal. When the conjugated polymer is not adjacent to a rough metal film, these excited conjugated polymer molecules are terminated by the radiative ͑k rad ͒ or nonradiative ͑k nonrad ͒ recombination rates.…”