Nitrogen Influence on the Photoluminescence Properties of Silicon Nanocrystals (original) (raw)
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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.
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.
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.
Journal of Surface Investigation. X-ray, Synchrotron and Neutron Techniques, 2012
The photoluminescence (PL) spectra and kinetics of amorphous and crystalline silicon nanoclus ters are investigated. The given nanoclusters are formed by thermal annealing of thin suboxide silicon films with different volume fractions of silicon. It is demonstrated that the PL intensity and lifetime of the ensem bles of silicon nanocrystals have a steplike dependence on the silicon volume fraction in the film. The influ ence of the percolation effect on the photoluminescence properties of the structures under study is discussed.
A novel method for the fabrication of nanometer-sized Si crystals in an amorphous SiO2 matrix by ion implantation and thermal processing is reported. Transmission electron microscopy indicates the formation of Si nanocrystais by annealing at 1 100 "t2, and the growth in average size of Si nanocrystals with increasing annealing time. The shape of the emission spectrum of the photoluminescence is found to be independent of both excitation energy and annealing time, while the excitation spectrum of photoluminescence increases as the photon energy increases and its shape depends on annealing time. The results indicate that the photons are absorbed by Si nanocrystals, for which the bandgap energy is modified by the quantum confinement effects, and the emission of photons is not due to direct electron-hole recombination inside Si nanocrystals but is related to defects probably at the interface between Si nanocrystals and SiO2. This method is fully compatible with silicon microelectronic technology.
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.
Effect of nitride passivation on the visible photoluminescence from Si-nanocrystals
Applied Physics Letters, 2004
The effect of nitride passivation on the visible photoluminescence from nanocrystal Si (nc-Si) is investigated. Silicon-rich silicon nitride (SRSN) and silicon-rich silicon oxide (SRSO), which consist of nc-Si embedded in silicon nitride and silicon oxide, respectively, were prepared by reactive ultrahigh vacuum ion beam sputter deposition followed by a high temperature anneal. Both SRSN and SRSO display photoluminescence peaks after high temperature annealing, coincident with the formation of Si nanocrystals, and similar changes in the peak luminescence position with the excess Si content. However, the luminescence peak positions from SRSN are blueshifted by about 0.6 eV over that of comparable SRSO such that its luminescence peaks in the visible range. The results demonstrate that control of the surface passivation is critical in controlling the nc-Si luminescence, and indicate the possibility of using nitride-passivated nc-Si for visible luminescence applications including white luminescence.
ACS Nano, 2013
Silicon nanocrystals (Si NCs) are attractive functional materials. They are compatible with standard electronics and communications platforms and are biocompatible. Numerous methods have been developed to realize size-controlled Si NC synthesis. While these procedures produce Si NCs that appear identical, their optical responses can differ dramatically. Si NCs prepared using high-temperature methods routinely exhibit photoluminescence agreeing with the effective mass approximation (EMA), while those prepared via solution methods exhibit blue emission that is somewhat independent of particle size. Despite many proposals, a definitive explanation for this difference has been elusive for no less than a decade. This apparent dichotomy brings into question our understanding of Si NC properties and potentially limits the scope of their application. The present contribution takes a substantial step forward toward identifying the origin of the blue emission that is not expected based upon EMA predictions. It describes a detailed comparison of Si NCs obtained from three of the most widely cited procedures as well as the conversion of red-emitting Si NCs to blue emitters upon exposure to nitrogen-containing reagents. Analysis of the evidence is consistent with the hypothesis that the presence of trace nitrogen and oxygen even at the parts per million level in Si NCs gives rise to the blue emission.
Journal of Applied Physics, 2002
The effect of ion irradiation on the formation of luminescent Si nanocrystals from silicon-rich silicon oxide ͑SRSO͒ films deposited by electron cyclotron resonance plasma-enhanced chemical vapor deposition ͑PECVD͒ whose Si content ranged from 33 to 50 at. % is investigated. As-deposited SRSO films contained a high density of irregular-shaped Si nanocrystals. Irradiating these films with 380 keV Si at room temperature to a dose of 5.7ϫ10 15 cm Ϫ2 prior to anneal at 1000°C is found to increase the luminescence intensity due to Si nanocrystals over the films. Based on the x-ray photoemission spectra and the dependence of the luminescence intensity on the irradiating ion dose, anneal time, and the silicon content of the film, we propose the destruction of pre-existing Si clusters by ion irradiation to be an important factor responsible for the observed enhancement of luminescence, and suggest that preanneal irradiation may be a viable method to control the formation of luminescent Si nanocrystals in PECVD-deposited silicon-rich silicon oxide.
Photoluminescent properties of nc-Si/SiO x nanosystems
Applied Nanoscience, 2018
In this work the nc-Si/SiO x nanosystems were obtained on the silicon substrate by means of evaporation of silicon powder in an oxidizing atmosphere. Then deposited SiO x films were irradiated from 226 Ra isotope and were annealed at 1000 °C to grow nc-Si. By means of the ellipsometric technique we studied the effect of annealing duration and irradiation on the optical characteristics of nc-Si/SiO x films. It was found that irradiation of obtained films promotes visible photoluminescence witdh maximum near 740 nm. More effective photon emission is caused by the change of nc-Si passivation conditions. Obtained experimental and theoretical results show the important influence of the Si/SiO x interface on the light emitting properties of nc-Si.