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...

We studied the influence of free carrier screening on the luminescence energy shift and carrier lifetime of InGaN multiple quantum wells (MQWs) mainly in relation to a quantum-confined Stark effect. We performed a systematic time-resolved photoluminescence measurement of MQWs for various carrier densities and three different well widths (2.5, 4.0, and 5.5 nm). We show that the energy shift and the change in carrier lifetime are explained well by the free carrier screening effect which compensates for the internal electric field.

The electron spin relaxation of InGaAs/InP multiple-quantum wells (MQW) is investigated using time-resolved polarization-dependent absorption measurement. The MQW has an excitonic absorption at 1.54 μm which is suitable for application in optical communications. A theoretical prediction assuming the D’yakonov-Perel’ interaction as the main relaxation mechanism gives a spin relaxation rate for the InGaAs quantum well over twice as high as that for the GaAs quantum well. The spin relaxation time measured at room temperature is 5.2 ps and found to be an order of magnitude faster than that of a GaAs quantum well.

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Radiative and nonradiative recombination dynamics in strained cubic (c-) In0.1Ga0.9N/c-GaN multiple quantum wells were studied using temperature-dependent time-resolved photoluminescence (TRPL) spectroscopy. In contrast to hexagonal InGaN quantum wells, low-excitation photoluminescence peak energy increased moderately with decreasing well thickness L and the PL lifetime did not strongly depend on L. The results clearly indicated that the piezoelectric field was not acting on the transition process. The TRPL signal was well fitted as a stretched exponential decay from 10 to 300 K, showing that the spontaneous emission is due to the radiative recombination of excitons localized in disordered quantum nanostructures such as In clusters. The localized states were considered to have two-dimensional density of states at 300 K (quantum disk size), since the radiative lifetime increased with increasing temperature above 150 K.