Luminescence Of Si Research Articles

Cavity-enhanced magnetic dipole resonance induced hot luminescence from hundred-nanometer-sized silicon spheres

Abstract In this paper, we demonstrate the first example of phonon-assisted hot luminescence (PAHL) emission from silicon (Si) spheres (diameter > 100nm) without using the plasmonic effect or quantum confinement effect. Instead, we excite the hot luminescence of Si by a strong thin-film-cavity-enhanced magnetic dipole resonance. The thin-film cavity (80 nm SiO2/Ag) shows a strong co-enhancement with the magnetic dipole resonance of Si sphere (diameter = 120 nm). The concentrated electromagnetic fields induce significant light–matter interaction. Our Si sphere coupled with a thin-film cavity achieves a 10-fold field enhancement relative to the Si sphere without an enhancement substrate. Furthermore, we experimentally use cavity-enhanced magnetic dipole resonance to a 50-fold enhancement in PAHL. The measured internal quantum efficiency for the visible light emitted from the Si spheres was approximately 2.4%. Furthermore, we demonstrate the tunability of emission peaks merely by adjusting the sizes of Si spheres using thermal oxidation and etching processes. For comparison, we calculated the peak wavelength (λ peak) sensitivities (Δλ peak/ΔDiameter) of Si spheres and Si QDs through Mie theory and effective mass approximation, respectively. The predicated peak sensitivities of the Si spheres ranged from 1.3 to 3.2; they were much more controllable than those of the Si QDs (200–400). Thus, the peak wavelengths of the PAHL of the Si spheres could be modulated and controlled much more precisely and readily than that of the Si QDs. With the tunability and strong electromagnetic field confinement, the cavity-enhanced magnetic dipole resonance appears to have great potential in the development of all-optical processing based on Si photonics.

Enhanced luminescence of Si(111) surface by localized surface plasmons of silver islands

The role of silver localized surface plasmons (LSPs) on the luminescence of a Si(111)-(7 × 7) surface has been investigated by scanning tunneling microscopy (STM) with a silver tip at 77 K. On a bare Si(111)-(7 × 7) surface, a characteristic peak at 1.85 eV dominates the STM-induced luminescence spectrum, although the luminescence intensity is extremely weak. Once Ag atoms are deposited onto the Si surface to form islands with a few atomic layers, it is found that the intensity of the characteristic peak from the Si surface underneath the Ag islands is significantly enhanced by about one order. In addition to the luminescence from the Si surface, light emission originating from the irradiation decay of the Ag plasmons is also detected. Such great enhancement of the luminescence from the Si surface is attributed to the strong coupling between the surface states of the Si and the LSPs of the Ag islands.

Hot carriers induced quenching of defects luminescence in Si doped AlN with Al core

We investigated the spatial cathodoluminescence (CL) quenching of Si doped AlN/Al shell/core particles along the radial direction. The quenching characteristic position gradually shifts to a more central location with emission wavelength increasing. This effect is due to the transport process of hot electrons, which produced by Al-plasmon decay via Landau damping. In this transport process, donor levels (Di) in AlN were partly occupied by hot electrons from Al core, which will reduce the quantum efficiency of recombination channel i (Di to Ai). A phenomenological theory has been used to discuss carriers recombination dynamics processes.

Composition and luminescence of Si and SiO<SUB align="right">2 layers co-implanted with Ga and N ions

With the aim to establish the possibility of synthesis of GaN inclusions by co-implantation of Ga and N ions in silicon and SiO2 films on a silicon substrate, the chemical composition and photoluminescence of implanted layers have been investigated. It is observed that the heavy loss of implanted atoms occurs owing to the out-diffusion (Ga from Si, and Ga and N from SiO2) in the process of post-implantation annealing. Preliminary implantation of nitrogen to form silicon nitride or oxynitride layers is shown to reduce the degree of impurity losses. In the photoluminescence spectrum of both Si and SiO2 subjected to Ga and N co-implantation, the band at 530-550 nm is present, which can be related to 'defect' luminescence of GaN.

Tunable luminescence of nanoporous silicon via electrochemical etching parameters

This paper reports the surface state induces a variation in light emission of nanoporous Si as a function of electrolyte condition, anode–cathode distance and aging in common chemical reagents to achieve strong and stable luminescence of Si semiconductor. The electrochemical derived nano Si was observed to have a nanoporous structure with the pore of about 20nm in the thickness of 50μm. The luminescence of nanoporous Si was showed enhancing in the sample with the HF/ethanol of 1:1 and the anode–cathode distance of about 5cm. As etched specimen, the luminescence of the nanoporous Si was centered at 800nm; however blue-shift when they were immersed in green chemical reagents. These results suggest that the potential application of electrochemical etching followed by green chemical treatment to tunable luminescence, which was potential application in nanoporous Si based devices and nanomedicine.

About dislocation and oxygen related luminescence of Si around 0.8 eV

AbstractIn conjunction with the two‐level model the temperature behaviour of the dislocation‐related D1‐peak follows the T‐behaviour of the band gap. Based on luminescence observations in our laboratory and on literature data we propose a ∼30 meV wide domain of the D1 peak. Altogether, the D1‐peak position ranges between about 0.76 eV at 300 K and nearly 0.84 eV at a few K. It was shown that the energetic shift for a certain temperature is caused by external electric fields, by excitation level, that affects the intrinsic dislocation field, and by elastic stress. The luminescence of oxygen‐related defects / precipitates might be described by a line at ∼ 0.77 eV (P‐line) that does not depend on temperature. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Strong luminescence from nanoporous Si with high degree of nanoporous structure by electrochemical etching of Si wafer

This article reports the first attempt to creation of a highly nanoporous silicon (Si) with a mesoporous structure to achieve strong and stable luminescence of Si, particularly, by applying an optimum voltage during electrochemical etching of Si wafer. The microstructure of nanoporous Si was depended on the electrochemical etched voltage that was observed to have a dendritic-like structure to a mesoporous one. The creation of mesoporous structure of the Si resulted in a significantly enhancing luminescence of the nanoporous Si, which was potential application in nanomedicine.

Effect of TEA on photoluminescence properties of PbS nanocrystalline thin films

In this work, the PbS nanocrystalline thin films were prepared by chemical bath deposition method on the glass and unpolished Si(100) substrates. Triethanolamine was used as additive in the aqueous solution, which resulted in the enhancement of the luminescence of nanocrystalline PbS thin films. The introduction of triethanolamine reduced the grain size and increased the optical band gap of the PbS nanoparticles. The crystalline size of PbS films deposited at two different bath temperatures of 25 °C (PbS-25) and 40 °C (PbS-40) and at different deposition times was estimated to be around 5–50 nm by XRD analyses. The films at 60 °C (PbS-60) were prepared and studied. The structural, morphological and optical properties of the obtained films were investigated. The energy-dispersive X-ray of the typical PbS film was presented, which confirmed the formation of PbS. The mechanism of growth of the PbS crystallites at different bath temperatures was described. The confinement was reflected in absorption and photoluminescence spectra. The variation of the photoluminescence intensity of PbS nanocrystals with triethanolamine molarity, deposition time and bath temperature was investigated. The PbS thin films were found to exhibit PL in both the ultraviolet and visible regions via quantum size effects, surface states and excitation wavelength variation. The luminescence of Si(100) substrate and PbS nanocrystalline films deposited on Si(100) were compared, and the results revealed that the PbS nanocrystals altered and notably enhanced the emission features of the Si(100) substrate. The multi-peak fitting using Gaussian function was employed for the photoluminescence spectrum of PbS on Si(100) substrate.

Optical and structural properties of nanocrystalline PbS thin film grown by CBD on Si(1 0 0) substrate

PbS nanocrystalline thin film was prepared by chemical bath deposition on Si(1 0 0) substrate at bath temperatures of 25, 45 and 65 °C. Triethanolamine was added to the aqueous solution, which decreased the grain size and increased the luminescence of the nanocrystalline PbS thin film. PbS nanocrystals were identified using XRD, TEM and AFM. The crystalline size of the PbS film deposited at different bath temperatures was estimated by XRD and TEM to be 7–12 nm. The growth mechanism of the PbS crystallites were described at different bath temperatures. The confinement was reflected in the absorption spectra, photoluminescence excitation and photoluminescence spectra. The luminescence of Si(1 0 0) substrate and PbS nanocrystalline film deposited on Si(1 0 0) were compared, and the results revealed that the PbS nanocrystals altered and notably enhanced the emission features of the Si(1 0 0) substrate. The shifting of the maximum photoluminescence emission wavelength of PbS nanocrystals with a change in bath temperature and the variation in photoluminescent intensity of PbS nanocrystals prepared at 25 °C versus deposition time were investigated. A single-peak fit of a Gaussian function was employed to discern the photoluminescence of PbS on Si(1 0 0) substrate.

Depth-resolved cathodoluminescence spectroscopy of silicon supersaturated with sulfur

We investigate the luminescence of Si supersaturated with S (Si:S) using depth-resolved cathodoluminescence spectroscopy and secondary ion mass spectroscopy as the S concentration is varied over 2 orders of magnitude (1018–1020 cm−3). In single-crystalline supersaturated Si:S, we identify strong luminescence from intra-gap states related to Si self-interstitials and a S-related luminescence at 0.85 eV, both of which show a strong dependence on S concentration in the supersaturated regime. Sufficiently high S concentrations in Si (>1020 cm−3) result in complete luminescence quenching, which we propose is a consequence of the overlapping of the defect band and conduction band.

Er3+ and Si luminescence of atomic layer deposited Er-doped Al2O3 thin films on Si(100)

Atomic layer deposition was used to deposit amorphous Er-doped Al2O3 films (0.9–6.2 at. % Er) on Si(100). The Er3+ photoluminescence (PL), Er3+ upconversion luminescence, as well as the Si PL and associated surface passivation properties of the films were studied and related to the structural change of the material during annealing. The PL signals from Er3+ and Si were strongly dependent on the annealing temperature (T = 450–1000 °C), but not directly influenced by the transition from an amorphous to a crystalline phase at T > 900 °C. For T > 650 °C, broad Er3+ PL centered at 1.54 μm (4I13/2) with a full width at half maximum of 55 nm was observed under excitation of 532 nm light. The PL signal reached a maximum for Er concentrations in the range of 2–3 at. %. Multiple photon upconversion luminescence was detected at 660 nm (4F9/2), 810 nm (4I9/2), and 980 nm (4I11/2), under excitation of 1480 nm light. The optical activation of Er3+ was related to the removal of quenching impurities, such as OH (3 at. % H present initially) as also indicated by thermal effusion experiments. In contrast to the Er3+ PL signal, the Si luminescence, and consequently the Si surface passivation, decreased for increasing annealing temperatures. This trade-off between surface passivation quality and Er3+ PL can be attributed to an opposite correlation with the decreasing hydrogen content in the films during thermal treatment.

Realization of sensitized erbium luminescence in Si–nanocrystal composites obtained from solution processable sol–gel derived materials

Silicon nanocrystals embedded in a silica matrix are good sensitizers of erbium ion photoemission and have application in photonic devices. We have developed a unique synthetic method to produce gram quantities of silicon nanocrystals embedded in a silica matrix containing erbium ions from solution borne precursors. This realization has facilitated a thorough study of the influence of erbium precursor on the chemical, physical and optical properties of the resulting materials. Three erbium precursors, erbium chloride, erbium tris(bis(trimethyl)silyl)amide, and erbium octanoate, were studied using Scanning Electron Microscopy, Energy Dispersive X-Ray Spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Photoluminescence Spectroscopy. It has been determined that the rare earth complexing ligand dramatically influences the erbium distribution homogeneity, solution processability, physical properties, and optical response. Most importantly we conclusively demonstrate that the optically active erbium ions in the resulting composites reside in the oxide matrix and not within the nanocrystals.

Influence of exposure to 980 nm laser radiation on the luminescence of Si:Er/O light-emitting diodes

Erbium (Er) codoping with oxygen (O) in Si is a well-known method for producing electroluminescent material radiating at 1.54 μm through a 4f shell transition of Er3+ ions. In this work the influence of exposure to 980 nm radiation on the electroluminescence (EL) of reverse biased Si:Er/O light-emitting diodes (LEDs), which give a strong room temperature 1.54 μm intensity, is presented and discussed. All the device layers, including Er/O doped Si sandwiched between two Si0.82Ge0.18 layers, have been grown on silicon on insulator substrates using molecular beam epitaxy and processed to fabricate edge emitting Si:Er/O waveguide LEDs. Electromagnetic mode confinement simulations have been performed to optimize the layer parameters for waveguiding. The temperature dependence of the 1.54 μm EL intensity exhibits an abnormal temperature quenching with a peak near −30 °C, and at −160 °C it has decreased by a factor of 5. However, irradiating the devices with a 980 nm laser gives an enhancement of the 1.54 μm EL intensity, which is more dramatic at low temperatures (e.g., −200 °C) where the quenched EL signal is increased up to almost the same level as at room temperature. The enhancement of the EL intensity is attributed to the photocurrent generated by the 980 nm laser, reducing the detrimental avalanche current.

Effects of Hydrogen on the Deep Levels in Si, ZnO and Diamond Studied by Cathodoluminescence

AbstractThe effects of hydrogen on the deep level luminescence in Si, ZnO and diamond were studied by means of cathodoluminescence. It is well known that most of the deep levels in Si are passivated by hydrogen. Scratch lines on Si surface, which do not show any characteristic luminescence, obtain so-called D-line luminescence by hydrogen plasma treatment. It indicates that only nonradiative defects are passivated but D-line luminescence is not passivated by hydrogenation. Contrarily, typical ZnO crystal shows the green emission, which is attributed to the point defects or impurities. Hydrogen completely passivates this green emission, and in turn, enhances the band edge emission. The effect of hydrogen passivation disappeared by the annealing at temperatures higher than 600 °C. Hydrogen behaves more peculiarly in diamond. The hydrogenated diamond film shows the characteristic emission around 2.3 eV in photon energy. Since it disappears by oxidization treatment, this emission is attributed to hydrogen at the subsurface region. The detailed study indicated that hydrogen in diamond has bistable states.

Time-Resolved Spectroscopic Studies of the Photoluminescence of Nanoporous Silicon: Effects of Lewis Acid/Base Exposure

Visible light emission emanating from nanostructured porous silicon is sensitive to adsorption of a number of small molecules, suggesting its utility as a chemical sensor. In this work we investigate the mechanistic origin of the diminution of the luminescence by n-propyl amine adsorption and restoration by trifluoroacetic acid, most sensitively by an examination of the changes in observed lifetime of the porous Si luminescence. This is quantified in terms of a stretched exponential model that is consistent with a distribution of luminescent centers in this nanophase material.

Mechanism on exciton-mediated energy transfer in erbium-doped silicon

Exciton-mediated energy transfer model in Er-doped silicon was presented. The emission intensity is related to optically active Er concentration, lifetime of excited Er 3+ ion and spontaneous emission. The thermal quenching of the Er luminescence in Si is caused by thermal ionization of Er-bound exciton complex and nonradiative energy backtransfer processes, which correspond to the activation energy of 6.6 and 47.4 meV, respectively. Er doping in silicon introduces donor states, a large enhancement in the electrical activation of Er (up to two orders of magnitude) is obtained by co-implanting Er with O. It appears that the donor states are the gateway to the optically active Er.

Room-temperature luminescence from rare-earth ions implanted into Si nanocrystals

Abstract Efficient room-temperature luminescence from rare earths contained in Si nanocrystals is reported. Si nanocrystals were formed by high-dose Si implantation into SiO2 followed by high-temperature annealing. Er implantation was then performed both in pure SiO2 and in SiO2 containing the nanocrystals. Luminescence measurements showed that the Er signal at 1.54 μm is two orders of magnitude higher in the sample containing the nanocrystals than in pure SiO2. Excitation spectroscopy demonstrated that, while within SiO2 Er is excited through direct photon absorption, excitation within the nanocrystals occurs via an efficient carrier-mediated process. These data demonstrate that the non-radiative processes usually limiting Er luminescence in Si are almost absent within the nanocrystals. Extension to other rare earths (namely Tm, Yb and Nd) is reported showing that the wavelength of emission can be properly tuned. The implications of these results are discussed.

Time-resolved study of yellow and blue luminescence in Si- and Mg-doped GaN

Time-resolved photoluminescence has been employed to study the donor-acceptor pair recombination kinetics of the yellow (∼2.3 eV) and blue (∼2.8 eV) luminescence bands in Si- and Mg-doped GaN layers, respectively. As the Si doping concentration in Si-doped GaN increases, the lifetime τ1/e of the yellow luminescence decreases, indicating that a shallow Si donor is the origin of the yellow luminescence. The blue luminescence is most likely due to a shallow Mg acceptor and a deep donor composed of a Mg acceptor-nitrogen vacancy complex, as seen by the independence of τ1/e on the Mg concentration measured by secondary ion mass spectroscopy in the range (2.5–6.0)×1019 cm−3. As the temperature is increased from 10 to 300 K, the lifetimes for the yellow and blue luminescence remain nearly constant, indicating that the distribution of electrons and holes bound to donors and acceptors does not change much with increasing temperature.

Formation and annealing of defects during high-temperature processing of ion-implanted epitaxial silicon: the role of dopant implants

We have investigated the optical and structural characteristics of defect evolution during high-temperature annealing of keV-ion-implanted epitaxial silicon using optical microscopy (OM), photoluminescence (PL) spectroscopy and transmission electron microscopy (TEM). Postimplantation annealing in oxygen ambient resulted in oxidation-induced stacking faults (OISFs) and dislocations. The PL spectrum of these samples is dominated primarily by a dislocation-related D1 line, which is particularly strong in Al-implanted samples as a consequence of the enhanced formation of dislocations with Al implantation. Comparative analysis of the PL signature and OM observations of defects for different implants suggests that D1 and D2 lines result from dislocations rather than in the OISFs. Indeed, it is found that OISFs act as a nonradiative recombination channel in the luminescence of Si. PL studies of N2-annealed samples indicate the formation of nonradiative defect centres. In the case of dopant implants, after rapid thermal annealing (RTA) for 2 min in N2 ambient, the specific signature of extended defects was found from PL studies, while TEM analysis reveals the presence of <111> precipitates located in a region with a high dislocation density. In comparison with other dopants, Al implants show an enhanced formation of extended defects, and they are found even at a depth beyond the end-of-ion range damage.

Enhanced rare earth luminescence in silicon nanocrystals

Efficient luminescence from rare earths ions embedded within silicon nanocrystals is reported. Samples were prepared either by high dose Si implantation into Si dioxide or by plasma enhanced chemical vapor deposition of sub-stoichiometric Si-rich oxides. In both cases nanocrystals were formed by Si precipitation and phase separation induced by high temperature annealing. Erbium was then introduced in SiO 2 samples containing the nanocrystals by ion implantation. Luminescence measurements showed that the Er signal at 1.54 μm is two orders of magnitude higher in the sample containing the nanocrystals with respect to pure SiO 2. Moreover, this enhanced luminescence is observed also for other rare earths (namely Yb, Tm and Nd). Excitation spectroscopy demonstrated that excitation within the nanocrystals occurs via an efficient carrier-mediated process. Indeed, with increasing rare earth luminescence the intrinsic nanocrystal luminescence is seen to decrease. Furthermore, the non-radiative processes usually limiting Er luminescence in Si, are shown to be almost absent within the nanocrystals. The implications of these results are discussed.