Chemical Insight into the Origin of Red and Blue Photoluminescence Arising from Freestanding Silicon Nanocrystals (original) (raw)
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Nitrogen Influence on the Photoluminescence Properties of Silicon Nanocrystals
MRS Proceedings, 2006
We have performed photoluminescence analysis of silicon rich oxide (SRO) and silicon rich oxynitride (SRON) samples deposited by plasma enhanced chemical vapor deposition (PECVD) and thermally annealed to cause the formation of silicon nanocrystals (Si-nc). Our purpose was to investigate the influence of nitrogen embedded into the oxide matrix on the photoluminescence properties of Si-nc. We found a large incorporation of silicon and a decrease of its diffusivity when the oxide is nitrogen rich. As a consequence the rate of crystallization for Si aggregates is slowed down when nitrogen is present in the oxide matrix.
Influence of nitrogen on the growth and luminescence of silicon nanocrystals embedded in silica
Journal of Applied Physics, 2009
Silicon nanocrystals ͑Si-ncs͒ have been produced by implantation of Si + in excess into SiO 2 followed by both annealing and passivation using argon or nitrogen. Nitrogen increases the photoluminescence ͑PL͒ emission and shifts the spectra toward the blue. The measured Si-nc diameter is 4.3 and 3.8 nm after annealing performed under Ar and N 2 , respectively. A significant quantity of nitrogen atoms has been detected in all samples by resonant nuclear reaction analysis ͑RNRA͒. The nitrogen concentration is significantly higher when the annealing and passivation are performed in a nitrogen environment, in agreement with a larger Si-N vibration signal on the Raman spectra. The depth profiles of nitrogen are very similar to those of Si-nc, suggesting that the N 2 molecules may diffuse in the SiO 2 during the annealing and then are trapped in proximity to the Si-nc. In addition to Si + , the implantation of N 2 + to concentrations of 3 and 6 at. % produced a decrease in the PL intensity ͑accentuated at the higher concentration͒ and an increase in the Raman signal associated to Si-N vibrations. These results suggest that a relatively low nitrogen atomic fraction enhances the PL emission, since a large nitrogen concentration impedes the formation of Si-nc thus significantly decreasing the PL intensity.
Photophysical Properties of Blue-Emitting Silicon Nanoparticles
Journal of Physical Chemistry C, 2009
Silicon nanoparticles with strong blue photoluminescence were synthesized by electrochemical etching of silicon wafers and ultrasonically removed under N 2 atmosphere in organic solvents to produce colloids. Thermal treatment leads to the formation of colloidal Si particles of 3 ± 1 nm diameter, which upon excitation with 340 -380 nm light exhibited room temperature luminescence in the range from 400 to 500 nm. The emission and the one-and two-photon excitation spectra of the particles are not sensitive to surface functionalization with methyl 2methylprop-2-enoate. However, the derivatized particles show higher emission quantum yields in air-saturated suspensions (44%) than the underivatized particles (27%), as well as higher stability of its dispersions.
Characterisation of silicon nanocrystals in silica and correlation with luminescence
Nanocrystalline silicon emits visible light (1.7eV) even though bulk Si has an indirect bandgap in the infra-red region. Si nanocrystals have been produced by ion implantation into an amorphous silica substrate followed by annealing at 1050 degrees Celsius. It was observed that the wavelength and intensity of emission is dependent on the ion implantation dose, annealing time and annealing temperature and is presumably related to the particle distribution. The mechanism for emission in such nanocrystals is as yet only partly understood, although recent results suggest interplay between quantum confinement and interface defect states.
Synthesis and Luminescent Properties of Silicon Nanocrystals
Nanocrystals and Nanostructures, 2018
Nowadays, study of silicon-based visible light-emitting devices has increased due to large-scale microelectronic integration. Since then different physical and chemical processes have been performed to convert bulk silicon (Si) into a light-emitting material. From discovery of Photoluminescence (PL) in porous Silicon by Canham, a new field of research was opened in optical properties of the Si nanocrystals (Si-NCs) embedded in a dielectric matrix, such as SRO (silicon-rich oxide) and SRN (silicon-rich nitride). In this respect, SRO films obtained by sputtering technique have proved to be an option for light-emitting capacitors (LECs). For the synthesis of SRO films, growth parameters should be considered; Si-excess, growth temperature and annealing temperature. Such parameters affect generation of radiative defects, distribution of Si-NCs and luminescent properties. In this chapter, we report synthesis, structural and luminescent properties of SRO monolayers and SRO/SiO 2 multilayers (MLs) obtained by sputtering technique modifying Si-excess, thickness and thermal treatments.
A complex study of the fast blue luminescence of oxidized silicon nanocrystals: the role of the core
Nanoscale, 2014
Silicon nanocrystals (SiNCs) smaller than 5 nm are a material with strong visible photoluminescence (PL). However, the physical origin of the PL, which, in the case of oxide-passivated SiNCs, is typically composed of a slow-decaying red-orange band (S-band) and of a fast-decaying blue-green band (F-band), is still not fully understood. Here we present a physical interpretation of the F-band origin based on the results of an experimental study, in which we combine temperature (4-296 K), temporally (picosecond resolution) and spectrally resolved luminescence spectroscopy of free-standing oxidepassivated SiNCs. Our complex study shows that the F-band red-shifts only by 35 meV with increasing temperature, which is almost 6 times less than the red-shift of the S-band in a similar temperature range. In addition, the F-band characteristic decay time obtained from a stretched-exponential fit decreases only slightly with increasing temperature. These data strongly suggest that the F-band arises from the core-related quasi-direct radiative recombination governed by slowly thermalizing photoholes.
XPS and SIMS investigation on the role of nitrogen in Si nanocrystals formation
Surface Science, 2005
Since the demonstration of optical gain in silicon nanocrystals, in the last few years several papers appeared in the literature reporting gain measurements in silicon nanocrystals embedded in a silica matrix produced by different techniques. However, it is still unclear which are the structural, physical and chemical factors that contribute to enhance photoluminescence and gain in this type of samples. In particular, the presence and the role of nitrogen in the SiO 2 matrix are in fact supposed to be essential factors in understanding the gain mechanism.
2013
Complex study of the fast blue luminescence of oxidized silicon nanocrystals: The role of the core Lukáš Ondič, 2, a) Katěrina Kůsová, Marc Ziegler, Ladislav Fekete, Viera Gärtnerová, Vladiḿır Cháb, Václav Holý, Onďrej Cibulka, Katěrina Herynková, Mathieu Gallart, Pierre Gilliot, Bernd Hönerlage, and Ivan Pelant Institute of Physics, Academy of Sciences of the Czech Republic, v.v.i., Cukrovarnická 10, 162 53, Prague 6, Czech Republic IPCMS, CNRS and Université de Strasbourg, 23, rue du Loess, F-67034 Strasbourg, France Institute of Physics, Academy of Sciences of the Czech Republic, v.v.i., Na Slovance 1999/2, 182 21, Prague 8, Czech Republic Faculty of Mathematics and Physics, Charles University, Ke Karlovu 3, 121 16 Prague 2, Czech Republic
International Journal of Nanotechnology, 2012
Silicon optoelectronics is an emerging technological platform, which holds promise for providing better performance, mostly in terms of lower dissipation losses, than the traditional electronics. However, a monolithic integrated light source is still missing since bulk silicon is a very poor light emitter due to its indirect bandgap. The situation dramatically changes when the size of the crystal is reduced down into nanometric dimension (<5 nm), when efficient room-temperature luminescence of these tiny silicon nanocrystals sets in. In this contribution, we present a study of silicon nanocrystals as light sources. We compare the photoluminescence properties of silicon nanocrystals with three different types of surface passivation (hydrogen, silicon oxide and methyl-based capping), which has substantial impact. We show that with sufficiently small sizes and suitable surface passivation, the photoluminescence properties of silicon nanocrystals can reach a level comparable with direct-bandgap semiconductor nanocrystals (radiative lifetime of 10 ns, stable macroscopic quantum yield of 20%). Apart from studying photoluminescence properties on a macroscopic level, we also carried out microscopical room-temperature single-nanocrystal photoluminescence spectroscopy experiments. These spectra revealed the occurrence of a fine structure (peaks 150 meV apart), practically identical with a structure already observed in single-nanocrystal spectra of silicon by other groups and very similar to a structure observed in a fundamentally different type of semiconductor nanocrystals (II-VI material). We propose that all these observations are linked with the same process, most probably the emission of trions in nanocrystals, although further measurements are necessary to support this claim.
Photoluminescence properties of size-controlled silicon nanocrystals at low temperatures
Journal of Applied Physics, 2009
This study attempts to clarify the origin of the temperature dependence of the photoluminescence (PL) spectra of silicon nanocrystals (Si-ncs) embedded in SiO2 from 5 to 300 K. For this purpose, size-controlled Si-ncs with a narrow size distribution were fabricated, using the SiO/SiO2 multilayer structure. The PL intensity is strongly temperature dependent and presents a maximum at around 70 K, depending on the Si-nc size and on the excitation power. The origin of this maximum is first discussed thanks to PL dynamics study and power dependence study. The evolution of the PL energy with temperature is also discussed. In bulk semiconductors the temperature dependence of the gap is generally well represented by Varshni’s law. Taking into account the quantum confinement energy, the PL energy of Si-ncs follows very well this law in the range 50–300 K. Below 50 K, a strong discrepancy to this law is observed characterized by a strong increase in the PL energy at low temperature, which is ...