Photoluminescence Enhancement of Silicon Quantum Dot Monolayer by Double Resonance Plasmonic Substrate

Abstract

A structure composed of a monolayer of luminescent silicon quantum dots (Si-QDs) and a silver (Ag) film over nanosphere (AgFON) plasmonic nanostructure is prepared by precisely controlling the distance. A AgFON structure modifies both the photoluminescence (PL) and the PL excitation (PLE) spectra of a Si-QD monolayer significantly. It is shown that the spectral shape is very sensitive to the spacer thickness and the wavelength dependence of the PL and PLE enhancement factors agrees well with the absorptance spectra. Due to multiple surface plasmon resonances of a AgFON structure, in proper spacer thicknesses, simultaneous enhancements of the excitation cross section and the emission rate are achieved. In the wavelength range where the absorption cross section of Si-QDs is small, the PL enhancement factor averaged in a relatively wide region (10 × 10 mm2) reaches 12.

Dual Management of Electrons and Photons to Get High‐Performance Light Emitting Devices Based on Si Nanowires and Si Quantum Dots with Al2O3‐Ag Hybrid Nanostructures

“…When Al 2 O 3 is inserted into our devices with prominent surface passivation effect, the lifetime becomes longer due to the suppression of ultrafast nonradiative recombination, which is related to surface defects such as that of Si dangling bonds . The lifetime also becomes longer when Ag nanoparticles are introduced into our devices and lifetime of the devices with Al 2 O 3 ‐Ag HNs is the longest due to the absorption section enlargement since the absorption peak appears in the short wavelength range with LSPR and this peak is blueshifted when Al 2 O 3 is introduced, as shown in Figure a . This means that more excitation light is absorbed, leading to more photogenerated carriers and corresponding the longer PL lifetime, because the lifetime of radiative recombination in Si QDs is much longer than that of nonradiative recombination.…”

“…PL intensity is obviously enhanced after insertion of Al 2 O 3 or Ag and the strongest PL is obtained with Al 2 O 3 ‐Ag HNs. It is worth noticing that with changing the four kinds of substrates, location of the PL peak is nearly the same, indicating that the coupling between LSPs and the incident excitation laser, instead of the internal emission light of Si QDs, may dominate the PL improvement with LSPR …”

“…As shown in Figure a, the absorption spectra of light emitting devices fabricated on four kinds of substrates are obtained through simply subtracting the reflectance measured by a Shimadzu UV‐3600 spectrophotometer since the transmittance is zero. An absorption peak located at ≈500 nm appears after the insertion of Ag because of LSPR effect, which is also affected by the dielectric changes after annealing . The absorption peak is blueshifted to ≈400 nm with Al 2 O 3 ‐Ag HNs and the absorption is obviously improved in the short wavelength range (200–440 nm), implying that through inserting Al 2 O 3 and Ag, the absorption of nanowire devices can be well adjusted.…”

“…The average lifetime (τ ave ) can be deduced through the functionwhere Γ E is the Euler gamma function . For all the devices, the lifetime is in the microsecond range (10–100 µs), which is corresponding to the lifetime range of photon‐generated carriers in Si QDs . When Al 2 O 3 is inserted into our devices with prominent surface passivation effect, the lifetime becomes longer due to the suppression of ultrafast nonradiative recombination, which is related to surface defects such as that of Si dangling bonds .…”

“…[24] These metal nanostructures are also considered to contribute to the local surface plasmon resonance (LSPR) effect, which can greatly enhance light intensity when the coupling between LSPs and incident excitation light or internal emission light happens. [29][30][31][32] Meanwhile, it is desired that with the introduction of Ag nanoparticles, the waveguide effect of Si NWs can be further promoted because of the prominent reflection effect. [33] As a result, the light extraction efficiency can be obviously improved.In the present work, hybrid nanostructures (HNs) of Al 2 O 3 / Ag are used in light emitting devices containing Al/p-type Si NW/Al 2 O 3 /Ag/Si QDs/n-type Si/indium tin oxide (ITO) in Silicon quantum dot (Si QD)-based light emitting devices are fabricated on Si nanowire (Si NW) arrays.…”