Silicon nanoparticles: Absorption, emission, and the nature of the electronic bandgap

Meier, Cedrik; Gondorf, Andreas; Lüttjohann, Stephan; Lorke, Axel; Wiggers, Hartmut

doi:10.1063/1.2720095

Cited by 152 publications

(146 citation statements)

References 17 publications

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“…Pump-power dependent measurements were also performed. In the acceptable range (1502350 nJ pulse 21 or 0.521.2 mJ cm 22 ), no pump intensity dependent dynamics were observed.…”

Section: Femtosecond Transient Absorption Experimentsmentioning

confidence: 99%

Ultrafast optical spectroscopy of surface-modified silicon quantum dots: unraveling the underlying mechanism of the ultrabright and color-tunable photoluminescence

Wang

et al. 2015

Light Sci Appl

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In this work, the fundamental mechanism of ultrabright fluorescence from surface-modified colloidal silicon quantum dots is investigated in depth using ultrafast spectroscopy. The underlying energy band structure corresponding to such highly efficient direct bandgap-like emissions in our surface-modified silicon quantum dots is unraveled by analyzing the transient optical spectrum, which demonstrates the significant effect of surface molecular engineering. It is observed that special surface modification, which creates novel surface states, is responsible for the different emission wavelengths and the significant improvement in the photoluminescence quantum yields. Following this essential understanding, surface-modified silicon quantum dots with deep blue to orange emission are successfully prepared without changing their sizes. Keywords: quantum confinement; silicon quantum dots; surface molecular engineering; ultrafast spectroscopy; wave function modification INTRODUCTIONCrystalline silicon has been the most important semiconductor material in the modern electronics industry due to its excellent electronic properties. However, as a well-known indirect bandgap semiconductor, the optical properties of crystalline silicon are relatively poor, which limits its applications in silicon photonics. To pursue the desired optical performance in silicon materials, nanostructured silicon objects with enhanced photoluminescence (PL) have attracted increasing interest. 1213 Most notably, due to the three-dimensional quantum confinement effect in silicon nanocrystals (Si NCs), the momentum conservation rule is relaxed, and the spatial distributions of photogenerated exciton wave functions tend to extend to the surface of nanoparticles, which provides an efficient approach to manipulate the energy structure of silicon. 14218 Thus, the excitonic emission from Si NCs are usually thought to follow three models: (i) 'direct' transition from a quantization-related bandgap; (ii) indirect approaches, i.e., with the help of other emission centers; and (iii) surface and/or strain engineering. 19 For the 'direct' approach, the observed size-dependent PL behavior in Si NCs can be well explained by the quantum confinement effect. However, such Si NCs can hold strong PL only in the deep red region with limited stability, and their PL lifetimes from these 'direct'

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“…Pump-power dependent measurements were also performed. In the acceptable range (1502350 nJ pulse 21 or 0.521.2 mJ cm 22 ), no pump intensity dependent dynamics were observed.…”

Section: Femtosecond Transient Absorption Experimentsmentioning

confidence: 99%

Ultrafast optical spectroscopy of surface-modified silicon quantum dots: unraveling the underlying mechanism of the ultrabright and color-tunable photoluminescence

Wang

et al. 2015

Light Sci Appl

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“…After the discovery of strong photoluminescence (PL) emission of porous silicon at room temperature 1,2 , silicon nanocrystals became the center of interest for many researchers 3,4 . The quantum confinement model is believed to be relevant for silicon nanocrystals 5,6 , coupling the observed increase of the band gap energy with the decrease of nanocrystal size.…”

Section: Introductionmentioning

confidence: 99%

Optical absorption cross section and quantum efficiency of a single silicon quantum dot

et al. 2013

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Optical absorption cross section and quantum efficiency of a single silicon quantum dot.In: Nanotechnology VI (pp. 876607- ABSTRACTDirect measurements of the optical absorption cross section (σ) and exciton lifetime are performed on a single silicon quantum dot fabricated by electron beam lithography (EBL), reactive ion etching (RIE) and oxidation. For this aim, single photon counting using, an avalanche photodiode detector (APD) is applied to record photoluminescence (PL) intensity traces under pulsed excitation. The PL decay is found to be of a mono-exponential character with a lifetime of 6.5 µs. By recording the photoluminescence rise time at different photon fluxes the absorption cross could be extracted yielding a value of 1.46×10 -14 cm 2 under 405 nm excitation wavelength. The PL quantum efficiency is found to be about 9% for the specified single silicon quantum dot.

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“…Figure 9.12 shows the results for the radiative lifetimes τ R and the oscillator strength f OSC for different emission energies, originating from particle diameters between 2.7 and 6.1 nm [36]. One can clearly recognize that the oscillator Fig.…”

Section: R R (T ) ∝ I (T ) · R Plmentioning

confidence: 95%

Optical Properties of Silicon Nanoparticles

Meier

Lorke

2012

Nanoparticles From the Gasphase

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This chapter reviews recent results on optical spectroscopy on silicon nanoparticles. The quantum confinement effect causing a spectral shift of the photoluminescence together with an intensity enhancement is discussed. The small spatial dimensions lead not only to a change of the electronic states, but affect also the vibronic spectrum as is seen in results on first-and second-order Raman scattering. Using time-resolved spectroscopy, the excitonic fine structure of silicon nanoparticles is investigated and a crossover of bright and dark exciton states is found. The analysis of the recombination dynamics allows to determine the size-dependence of the oscillator strength, which is in the order of 10 −5 and increases with decreasing particle size. Finally, we demonstrate an electroluminescence device based on silicon particles using impact ionization. IntroductionDue to the fact that most physical, chemical, and mechanical properties of nanostructured materials are determined by their structure, especially by geometry and size, many applications have been developed based on fundamental research in this field. The reasons for the novel effects in such nanomaterials are manifold, ranging from surface effects, e.g., in nanoparticle based gas sensors, to quantum confinement effects in sufficiently small structures. Among the inorganic materials used

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Silicon nanoparticles: Absorption, emission, and the nature of the electronic bandgap

Cited by 152 publications

References 17 publications

Ultrafast optical spectroscopy of surface-modified silicon quantum dots: unraveling the underlying mechanism of the ultrabright and color-tunable photoluminescence

Ultrafast optical spectroscopy of surface-modified silicon quantum dots: unraveling the underlying mechanism of the ultrabright and color-tunable photoluminescence

Optical absorption cross section and quantum efficiency of a single silicon quantum dot

Optical Properties of Silicon Nanoparticles

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