Theoretical aspects of the luminescence of porous silicon

Delerue, Christophe; Allan, G.; Lannoo, M.

doi:10.1103/physrevb.48.11024

Cited by 985 publications

(559 citation statements)

References 54 publications

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“…As can be clearly seen in this figure, all previous models yield values around the commonly assumed electron-hole PCE in Si, 3.63 eV (i.e. the direct band gap, as discussed above), which is the result of long-timescale experiments [35]- [40]. These values differ from the experiments with damped recombination [34] by a factor of two or more, while our simulation compares very well with the experimental data (figure 7).…”

Section: Dependence Of Eeg On Fluencementioning

confidence: 69%

“…Such an overestimation was also found experimentally decades ago [34], and several models were proposed for a better estimation of the number of free electrons (see the description of theoretical models in [37] and numerical models in [33] and the references therein). One of the most common models involves the application of the direct band gap of the material [35]. However, impact ionization, as well as Auger-like processes, are restricted by energy and momentum conservation [14].…”

Section: Effective Energy Gapmentioning

confidence: 99%

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Transient dynamics of the electronic subsystem of semiconductors irradiated with an ultrashort vacuum ultraviolet laser pulse

Medvedev¹,

Rethfeld²

2010

New J. Phys.

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Abstract. The irradiation of semiconductors with ultrashort laser pulses causes excitation of electrons from bound states (the valence band and deep atomic shells) to the conduction band, which produces non-equilibrium highly energetic free electrons. We apply a Monte-Carlo simulation technique to study the ionization and excitation of the electronic subsystem of a solid silicon target irradiated with a femtosecond laser pulse, obtaining the transient distribution of electrons within the conduction band. We take into account the electronic band structure and Pauli's principle for excited electrons. Secondary excitation and ionization processes induced by electrons in the conduction band and holes in the valence band were also included and simulated event by event. The temporal distributions of the density and the energy of excited electrons are calculated and discussed. We demonstrate that, due to the energy used to overcome the ionization potential, the final kinetic energy of the free electrons is significantly less than the total energy provided by the laser pulse. We extend the concept of an 'effective energy gap' for multiple electronic excitations, which can be applied to estimate the free-electron density after high-intensity vacuum ultraviolet (VUV) laser pulse irradiation. The effective energy gap depends on both the properties of the material and the laser pulse parameters. The concept provides a fundamental understanding of the experimentally accessible pair creation energy measured in the limit of long times.

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Section: Dependence Of Eeg On Fluencementioning

confidence: 69%

Section: Effective Energy Gapmentioning

confidence: 99%

Transient dynamics of the electronic subsystem of semiconductors irradiated with an ultrashort vacuum ultraviolet laser pulse

Medvedev¹,

Rethfeld²

2010

New J. Phys.

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“…13,49,57,65,67,[71][72][73] In fact, it has been suggested that dangling bonds form highly efficient non-radiative recombination centers, such that the presence of a single dangling bond in a Si nanocrystal is sufficient to prevent PL. 49 Experimentally, dangling bonds have been shown to be present both on the surface of silicon nanoparticles, 74 as well as at the crystal-oxide interface of oxidized Si NPs. 56,72 In these studies, the presence of Sibased radicals was correlated with reduced PL intensities, which is in good agreement with theoretical predictions.…”

Section: Effect Of Defects On Photoluminescence From Silicon Nanopartmentioning

confidence: 99%

“…49 In the study, the authors analyzed the mechanism of charge carrier trapping at an unoccupied trap state that was located just below the conduction band minimum in energy. They reported that for nanocrystalline silicon with bandgaps less than 2.2 eV (560 nm), nonradiative recombination of an exciton at a neutral dangling bond can occur quickly (rate = ~10 5 -10 7 ms -1 ) via a two step process in which the electron and hole are trapped sequentially.…”

Section: Effect Of Defects On Photoluminescence From Silicon Nanopartmentioning

confidence: 99%

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Investigation into Effects of Instability and Reactivity of Hydride-Passivated Silicon Nanoparticles on Interband Photoluminescence

Radlinger¹

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While silicon has long been utilized for its electronic properties, its use as an optical material has largely been limited due to the poor efficiency of interband transitions. However, discovery of visible photoluminescence (PL) from nanocrystalline silicon in 1990 triggered many ensuing research efforts to optimize PL from nanocrystalline silicon for optical applications. Currently, use of photoluminescent silicon nanoparticles (Si NPs) is commercially limited by: 1) the instability of the energy and intensity of the PL, and 2) the low quantum yield of interband PL from Si NPs.Herein, red-emitting, hydrogen-passivated silicon nanoparticles (H-Si NPs) were synthesized by thermally-induced disproportionation of a HSiCl 3 -derived (HSiO 1.5 )n polymer. The H-Si NPs produced by this method were then subjected to various chemical and physical environments to assess the long-term stability of the optical properties as a function of changing surface composition. This dissertation is intended to elucidate correlations between the reported PL instability and the observed changes in the Si NP surface chemistry over time and as a function of environment.First, the stability of the H-Si NP surface at slightly elevated temperatures towards reactivity with a simple alkane was probed. The H-Si NPs were observed by FT-IR spectroscopy to undergo partial hydrosilylation upon heating in refluxing hexane, in addition to varying degrees of surface oxidation. The unexpected reactivity of the Si surface in n-hexane supports the unstable nature of the H-Si NP surface, and furthermore implicates the presence of highly-reactive Si radicals on the surfaces of the Si NPs. We propose that reaction of alkene impurities with the Si surface radicals is largely responsible for the observed surface alkylation. However, we also present an alternate ii mechanism by which Si surface radicals could react with alkanes to result in alkylation of the surface.Next, the energy and intensity stability of the interband PL from H-Si NPs in the presence of a radical trap was probed. Upon addition of (2,2,6,6,-tetramethyl-piperidin-1-yl)oxyl (TEMPO), the energy and intensity of the interband transition was observed to change over time, dependent on the reaction conditions. First, when the reaction occurred at 4ºC with minimal light exposure, the interband transition exhibited a gradual hypsochromic shift to between 595 nm and 655 nm, versus the λ max of the original low energy emission peak at 700 nm, depending on the amount of TEMPO in the sample.Second, when the reaction proceeded at room temperature with frequent exposure to 360 nm irradiation, the original interband transition at 660 nm was quenched while a new peak at 575 nm developed. Based on all the data collected and analyzed, we assign the 595 -655 nm transition as due to interband exciton recombination from Si NPs with reduced diameters relative to the original Si NPs. We furthermore assign the 575 nm transition as due to an oxide-related defect state resulting from rapid oxidation of pho...

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