Quantum confinement in Si nanocrystals

Delley, B.; Steigmeier, E. F.

doi:10.1103/physrevb.47.1397

Cited by 477 publications

(253 citation statements)

References 16 publications

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“…A consensus has been reached that highly-localised defects at the Si/SiO 2 interface 8,9,10 and the quantum confinement of excitons 15,16,17 both play important roles, but it is difficult to experimentally distinguish the mechanisms in the radiative emission 9,10 , especially since the interface-related PL depends on nanocrystal size 8,9,10,11 . Here, we report the use of high-field magneto-PL (≤50 T) experiments to directly probe the extent of the wave function responsible for the PL 18,19 , and demonstrate that the PL is dominated by defect states.…”

Section: Introductionmentioning

confidence: 99%

Classification and control of the origin of photoluminescence from Si nanocrystals

et al. 2008

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Silicon dominates the electronics industry, but its poor optical properties mean that III-V compound semiconductors are preferred for photonics applications. Photoluminescence at visible wavelengths was observed from porous Si at room temperature in 1990, but the origin of these photons -highly-localized defect states or quantum confinement effects? -has been the subject of intense debate ever since. Since then attention has shifted from porous Si to Si nanocrystals, but the same fundamental question about the origin of the photoluminescence has remained. Here we show, based on measurements in high magnetic fields, that defects are the dominant source of light from Si nanocrystals. Moreover, we show that it is possible to control the origin of the photoluminescence in a single sample: passivation with hydrogen removes the defects, resulting in photoluminescence from quantum-confined states, but subsequent UV illumination reintroduces the defects, making them the origin of the light again.

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Section: Introductionmentioning

confidence: 99%

Classification and control of the origin of photoluminescence from Si nanocrystals

et al. 2008

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“…The earlier studies on the optical properties of silicon and hydrogenated silicon clusters focused on the size dependence of the PL and photo-absorption 3,[17][18][19][20][21] . Some of these studies ignored the influence of oscillator strength's (electric dipole matrix elements) and hence were not in good agreement with the experimental data.…”

Section: Introductionmentioning

confidence: 99%

Photo-absorption spectra of small hydrogenated silicon clusters using the time-dependent density functional theory

Thingna¹,

Prasad²,

Auluck³

2011

Journal of Physics and Chemistry of Solids

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We present a systematic study of the photo-absorption spectra of various Si n H m clusters (n=1-10, m=1-14) using the time-dependent density functional theory (TDDFT). The method uses a real-time, real-space implementation of TDDFT involving full propagation of the time dependent Kohn-Sham equations. Our results for SiH 4 and Si 2 H 6 show good agreement with the earlier calculations and experimental data. We find that for small clusters (n<7) the photo-absorption spectrum is atomic-like while for the larger clusters it shows bulk-like behaviour. We study the photo-absorption spectra of silicon clusters as a function of hydrogenation. For single hydrogenation, we find that in general, the absorption optical gap decreases and as the number of silicon atoms increase the effect of a single hydrogen atom on the optical gap diminishes. For further hydrogenation the optical gap increases and for the fully hydrogenated clusters the optical gap is larger compared to corresponding pure silicon clusters. PACS number(s): 78.67. -n, 73.22.-f, 71.15 Pd PACS numbers:

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“…Confinement leads to a widening of the band gap and increased oscillator strength for the transition (e.g. [5]). The extent of changes (direct versus indirect) in the band structure of nanostructures of silicon is still a controversial topic (e.g.…”

Section: Introductionmentioning

confidence: 99%

Exciton dispersion in silicon nanostructures formed by intense, ultra-fast electronic excitation

Hamza

Newman

Thielen

et al. 2003

Applied Physics A: Materials Science & Processing

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The intense, ultra-fast electronic excitation of clean silicon (100)-(2 × 1) surfaces leads to the formation of silicon nanostructures embedded in silicon, which photoluminesce in the yellow-green (∼ 2-eV band gap). The silicon surfaces were irradiated with slow, highly charged ions (e.g. Xe 44+ and Au 53+ ) to produce the ultra-fast electronic excitation. The observation of excitonic features in the luminescence from these nanostructures has recently been reported. In this paper we report the dispersion of the excitonic features with laser excitation energy. A phonon-scattering process is proposed to explain the observed dispersion. Bulk silicon is a poor light emitter owing to its indirect band gap. Since 1990 many authors have observed visible-light emission from silicon nanostructures. Two of the prominent examples are porous silicon (e.g. [1,2]) and silicon nanoclusters in silica (e.g. [3]). Visible emission has also been observed from one-dimensionally confined silicon in silicon/SiO 2 superlattices [4]. Many authors show that the visible emission can be due to quantum confinement of the excitation to a structure with less than 5-nm radius (Bohr radius of an exciton in silicon) (e.g. [2]). Confinement leads to a widening of the band gap and increased oscillator strength for the transition (e.g. [5]). The extent of changes (direct versus indirect) in the band structure of nanostructures of silicon is still a controversial topic (e.g. [6,7]).Recently, we have briefly reported the observation of light emission from nanostructures on silicon formed by intense, ultra-fast electronic excitation [8]. The intense, ultra-fast electronic excitation of clean silicon (100)-(2 × 1) surfaces leads to the formation of silicon nanostructures embedded in silicon, which photoluminesce at ∼560-nm wavelength (∼ 2-eV band gap). The silicon surfaces were irradiated with slow, and Au 53+ ) to produce the electronic excitation. The observation of excitonic features in the luminescence is particularly unusual for silicon nanostructures. The temperature dependence of the luminescence and the measurement of the triplet-singlet splitting of the emission strongly support the excitonic assignment. Intense, ultra-fast electronic excitation of a semiconductor surface such as silicon leads to the promotion of many (> 10 3 ) valence (bonding) electrons into the conduction bands (antibonding states). The promotion of a single electron or even many electrons into antibonding states does not impart a sufficient force for a sufficient length of time to cause displacement of the atomic nuclei. In contrast, the high density of electrons in antibonding states created by an intense, ultra-fast electronic excitation can impart an impulse leading to atomic displacements [9][10][11][12]. Direct evidence of atomic motion on a ∼160-fs time scale due to antibonding state excitation is reported by Petek et al. [13].The deposition of potential energy from slow, highly charged ions (SHCI) such as Xe 44+ (616-keV kinetic energy in this study) in se...

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Quantum confinement in Si nanocrystals

Cited by 477 publications

References 16 publications

Classification and control of the origin of photoluminescence from Si nanocrystals

Classification and control of the origin of photoluminescence from Si nanocrystals

Photo-absorption spectra of small hydrogenated silicon clusters using the time-dependent density functional theory

Exciton dispersion in silicon nanostructures formed by intense, ultra-fast electronic excitation

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