Photoluminescence Of Si Research Articles

Light‐Induced Degradation Transition Energy Barrier Measured by Photoluminescence Spectra in Si:In

The impact of light‐induced degradation (LID) treatments is investigated using low‐temperature photoluminescence in Si:In. A feature called as the P‐line, located at 1.118 eV, provides information on the decisive energy barrier for the LID effect. The intensity of the P‐line can be reproducibly influenced by illumination and annealing treatments. The decay of the P‐line after quenching, illumination, and moderate annealing of the silicon samples is measured as function of time and annealing temperature. Both indium‐doped as‐grown Czochralski and indium implanted float‐zone silicon wafers are examined and their behavior is compared. Based on these measurements, an energy barrier for the P‐line defect transition is calculated. The LID defect model is used to discuss the results.

Driving Third-Order Optical Nonlinearities in Photoluminescent Si Nanoparticles by Nitrogen Co-Implantation in a Silica Matrix.

The photoluminescence and third-order nonlinear optical effects of co-implanted silicon nanoparticles and nitrogen ions in a silica matrix were studied. Experimental evidence shows the potential of nitrogen ions for changing optical properties exhibited by silicon nanoparticles implanted in an integrated system. The modification of the optical bandgap and photoluminescent intensity in the studied nanomaterials by the incorporation of nitrogen was analyzed. Standard two−wave mixing experiments were conducted using nanosecond and picosecond laser pulses at 532 nm wavelength. At this off-resonance condition, only multiphoton excitation can promote electrons at energies above the optical bandgap of the silicon nanoparticles. The picosecond results show that the co-implanted sample with nitrogen exhibits a three-fold enhancement of the nonlinear Kerr response. Femtosecond z-scan measurements were undertaken at 800 nm in order to explore the modification of the ultrafast nonlinear response of the samples that revealed a purely electronic Kerr nonlinearity together to saturable absorption of the SiNPs in the near-infrared. Remarkably, femtosecond results reveal that nitrogen co-implantation in the SiNPs system derives from the quenching of the third-order nonlinear optical behavior. These findings pointed out a simple approach for engineering the optical bandgap of nanocomposites, which can be controlled by a doping process based on ion-implanted nitrogen. It is highlighted that the enhanced light-matter interactions induced by nitrogen implantation can be useful for developing nonlinear integrated silicon photonics nanodevices with low power excitation.

Response of Photoluminescence of H-Terminated and Hydrosilylated Porous Si Powders to Rinsing and Temperature

The photoluminescence (PL) response of porous Si has potential applications in a number of sensor and bioimaging techniques. However, many questions still remain regarding how to stabilize and enhance the PL signal, as well as how PL responds to environmental factors. Regenerative electroless etching (ReEtching) was used to produce photoluminescent porous Si directly from Si powder. As etched, the material was H-terminated. The intensity and peak wavelength were greatly affected by the rinsing protocol employed. The highest intensity and bluest PL were obtained when dilute HCl(aq) rinsing was followed by pentane wetting and vacuum oven drying. Roughly half of the hydrogen coverage was replaced with –RCOOH groups by thermal hydrosilylation. Hydrosilylated porous Si exhibited greater stability in aqueous solutions than H-terminated porous Si. Pickling of hydrosilylated porous Si in phosphate buffer was used to increase the PL intensity without significantly shifting the PL wavelength. PL intensity, wavelength and peak shape responded linearly with temperature change in a manner that was specific to the surface termination, which could facilitate the use of these parameters in a differential sensor scheme that exploits the inherent inhomogeneities of porous Si PL response.

Time-resolved photoluminescence properties of ion-beam-synthesized β-FeSi2 and Si-implanted Si

Temporal decay characteristics of 1.54 µm photoluminescence (PL) were investigated in β-FeSi2 and Si-implanted Si samples grown by ion-beam-synthesis (IBS). In the samples, the band-edge PL of β-FeSi2 (A-band) and the dislocation-related PL (D1-band) of Si were both observed at ∼0.8 eV. Regarding the dependence of the PL decay curves on excitation power density (P), PL decay curves without extrinsic effects were obtained at a low P of P ≤ 4.3 mW/cm2. The PL decay times obtained at a low P showed clear differences between the A-band and the D1-line. The result showed that the band-edge PL of β-FeSi2 was distinguished from the dislocation-related PL of Si by the PL decay times. The intrinsic PL decay times of β-FeSi2 were determined to be τ1 = 70–100 ns and τ2 = 550–670 ns at 5 K.

Microstructural and photoluminescent properties of terbium-doped SiC nanotubes prepared by sputtering using electrospun polymer templates

Terbium-doped SiC (SiC:Tb) nanotubes were prepared by sputtering using electrospun PVP nanofiber templates, followed by annealing in air and carbothermal reduction. Results showed that the obtained SiC:Tb nanotubes are 100–200nm in outer diameter and 20–50nm in wall thickness. Photoluminescence (PL) tests indicated that the as-obtained amorphous SiC:Tb nanotubes exhibited a rather low PL from the doped Tb3+ ions, but a strong self-active PL of Si–C–O defects. While the carbothermal treatments at 800 or 900°C can greatly enhance the Tb-related PL, further increasing the calcination temperature to 1200°C will force most of the Tb ions to separate out to the surface of the nanotubes, which is mainly responsible for the second increase in the Tb-related PL.

UV and air stability of high-efficiency photoluminescent silicon nanocrystals

The effects of UV light and air exposure on the photoluminescent properties of nonthermal plasma-synthesized silicon nanocrystals (Si NCs) were investigated. Si NCs with high-efficiency photoluminescence (PL) have been achieved via a post-synthesis hydrosilylation process. Photobleaching is observed within the first few hours of ultra-violet (UV) irradiation. Equilibrium is reached after ∼4h of UV exposure wherein the Si NCs are able to retain 52% of the initially measured PL quantum yield (PLQY). UV-treated Si NCs showed recovery of PL with time. Gas-phase passivation of Si NCs by hydrogen afterglow injection improves PLQY and PL stability against UV and air exposure. Additionally, phosphorous doping can also improve UV stability of photoluminescent Si NCs.

Effect of ion doping on the dislocation-related photoluminescence in Si+-implanted silicon

The study is concerned with the effect of the additional implantation of Si samples with C+, O+, B+, P+, and Ge+ impurity ions followed by annealing at 800°C on the behavior of the dislocation photoluminescence line D1, induced in the samples by implantation with Si+ ions at a stabilized temperature followed by annealing in an oxidizing Cl-containing atmosphere. It is established that the intensity of the D1 line strongly depends on the type of incorporated atoms and the dose of additional implantation. An increase in the D1 line intensity is observed upon implantation with oxygen and boron; at the same time, in other cases, the D1 luminescence line is found to be quenched. The mechanisms of such behavior, specifically, the role of oxygen and its interaction with implanted impurities are discussed.

Effect of the annealing temperature on the low-temperature photoluminescence in Si:Er light-emitting structures grown by molecular-beam epitaxy

The photoluminescence spectra of light-emitting structures based on silicon doped with erbium during the course of molecular-beam epitaxy at a temperature of 500°C are studied at 4.2 K on being annealed at 800–900°C. Three sets of lines belonging to the emitting centers of erbium in silicon with a low oxygen-impurity concentration are revealed.

Synthesis of photoluminescent Si–O–C(–H) ceramics from oxidation-cured polycarbosilane by hydrogen decarbonization

Polycarbosilane powder, formed by a desaturation process, was oxidation-cured at 180–340°C and pyrolyzed in a hydrogen atmosphere to obtain Si–O–C(–H) ceramics with low carbon contents. FT-IR was used to investigate the progress of the oxidation curing. Suitable curing conditions were found to be 240°C for 20h, and the powders obtained after the pyrolysis exhibited intense luminescence under UV irradiation. The chemical compositions of the resulting Si–O–C(–H) ceramics were close to the stoichiometric (SiO2)–x(SiC)–y(H) compositions. The luminescence properties of these Si–O–C(–H) ceramics were analyzed by using time-resolved photoluminescence spectra.

Blue photoluminescent Si nanocrystals prepared by high-current pulsed electron beam irradiation

Si nanocrystals (Si-ncs) were prepared from n-type Si (100) wafers by using high-current pulsed electron beam irradiation in vacuum. High density (9.7 × 1014 cm−2) ultrafine Si-ncs (∼3 nm) embedded in amorphous Si layers (∼60 nm) exhibit blue photoluminescence emission at room temperature which can be attributed to the quantum confinement size effect. The pulse number is a key parameter which influences the photoluminescence intensity. Possible formation mechanisms of Si-ncs are discussed.

Freestanding monolithic silicon aerogels

The electrical, optical, and (bio)chemical properties of porous Si have attracted considerable interest for battery, solar cell, display, sensor, biomedical, and other applications. Free-standing monolithic Si aerogels have been generated for the first time via low-temperature magnesiothermic reduction of SiO2 aerogels. Under appropriate conditions, the reaction of Mg gas with SiO2 produced a co-continuous mixture of predominantly MgO and Si. Selective MgO dissolution then yielded nanocrystalline, porous, photoluminescent Si aerogels with a high degree of porosity (97.3 vol%) and a high specific surface area (615 m2 g−1).

표면 알킬기를 갖는 실리콘 나노입자의 One-Pot 용액환원 합성

가시광 영역에서 강한 광루미네선스(photoluminescence, PL) 특성이 있는 실리콘 나노입자는, 생물학적 형광 이미징, RGB(red, green, blue) 디스플레이, 포토닉스, 광전소자 등의 응용소재로 개발될 수 있어 많은 연구가 수행되고 있다. 실리콘 나노입자의 광학적 및 물리화학적 특성을 이용한 실용적인 응용 및 개발을 위해서는 그 특성의 조절이 용이한 제조법 개발이 필수적이다. 본 연구에서는 Na(naphthalide)를 환원제로 사용한 용액환원법을 이용하여 한 단계로 입자표면이 알킬기로 안정화된 평균 <10 nm 크기의 실리콘 나노입자를 합성할 수 있는 방안을 시도하였다. 이를 위하여 실리콘 전구체로 알킬기를 포함하고 있는 (Octyl)<TEX>$SiCl_3$</TEX> 단독 또는 (Octyl)<TEX>$SiCl_3$</TEX>와 <TEX>$SiCl_4$</TEX>의 혼합물을 사용하여 Si-Cl 결합의 환원을 통한 입자의 형성과 동시에 반응물에 포함된 Octyl 기에 의한 표면 안정화를 한번에 달성할 수 있었다. 합성한 실리콘 입자의 TEM/EDS, FTIR 분석결과 입자의 크기는 <10 nm이며, 표면이 알킬기로 덮여있어 소수성 용제인 헥산에 쉽게 용해되었으며 입자표면은 소량의 산화된 Si-O-Si 그룹을 포함하고 있었다. UV-vis 및 PL 분석결과 표면 알킬기를 포함하는 실리콘 나노입자의 전형적인 광 특성을 보여 간단한 반응단계를 통하여 표면이 Octyl기로 덮인 실리콘 나노입자를 합성할 수 있음을 보였다. 본 연구에서 시도한 합성법을 응용할 경우, 향 후 실리콘 나노입자의 표면에 다양한 기능기를 one-pot으로 도입할 수 있을 것으로 기대된다. Silicon nanoparticles have attracted a great deal of scientific interests due to its intense photoluminescence in the visible spectral region and its potential applications in biological fluorescence maker, RGB (red, green, blue) display, photonics and photovoltaics etc. Practical applications making use of optical and physicochemical properties of Si nanoparticles requires an efficient synthetic method which allows easy modulation of their size, size distribution as well as surface functionalities etc. In this study, a one-pot solution reduction scheme is attempted to prepare alkyl-terminated Si nanoparticles (<10 nm) with Si precursors, (Octyl)<TEX>$SiCl_3$</TEX> or mixture of (Octyl)<TEX>$SiCl_3$</TEX> and <TEX>$SiCl_4$</TEX>, containing alkyl-groups using Na(naphthalide) as reducing agent. The surface capping of Si nanoparticles with octyl-groups as well as Si nanoparticle formation was achieved in one-pot reaction. The hexane soluble Si nanoparticles with octyl-termination were in the range of 2-10 nm by TEM and some oxide groups (Si-O-Si) was present on the surface by EDS/FTIR analyses. The optical properties of Si nanoparticles measured by UV-vis and PL evidenced that photoluminescent Si nanoparticles with alkyl-termination was successfully synthesized by solution reduction of alkyl-containing Si precursors in one-pot reaction.

Photoluminescence of Si from Si nanocrystal-doped SiO 2/Si multilayered sample

A multilayered Si nanocrystal-doped SiO 2/Si (or Si-nc:SiO 2/Si) sample structure is studied to acquire strong photoluminescence (PL) emission of Si via modulating excess Si concentration. The Si-nc:SiO 2 results from SiO thin film after thermal annealing. The total thickness of SiO layer remains 150 nm, and is partitioned equally into a number of sublayers ( N = 3, 5, 10, or 30) by Si interlayers. For each N-layered sample, a maximal PL intensity of Si can be obtained via optimizing the thickness of Si interlayer (or d Si). This maximal PL intensity varies with N, but the ratio of Si to O is nearly a constant. The brightest sample is found to be that of N = 10 and d Si = 1 nm, whose PL intensity is ∼5 times that of N = 1 without additional Si doping, and ∼2.5 times that of Si-nc:SiO 2 prepared by co-evaporating of SiO and Si at the same optimized ratio of Si to O. Discussions are made based on PL, TEM, EDX and reflectance measurements.

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 &amp;gt; 900 °C. For T &amp;gt; 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.

Specific features of the mechanisms of excitation of erbium photoluminescence in epitaxial Si:Er/Si structures

The excitation spectra and kinetics of erbium photoluminescence and silicon interband photoluminescence in Si:Er/Si structures under conditions of high-intensity pulse optical excitation are studied. It is shown that, in the interband photoluminescence spectra of the Si:Er/Si structures, both the luminescence of free excitons and the emission associated with the electron-hole plasma can be observed, depending on the excitation power and wavelength. It is found that the formation of a peak in the erbium photoluminescence excitation spectra at high pumping powers correlates with the Mott transition from the exciton gas to the electron-hole plasma. It is demonstrated that, in the Si:Er/Si structures, the characteristic rise times of erbium photoluminescence substantially depend on the concentration of charge carriers.

Photoluminescence of Si+ and C+ implanted polymers

Visible photoluminescence (PL) of ion implanted polymers was studied. Different polymer materials were used for the purpose: polypropylene (PP), poly-tetrafluor-ethylene (Teflon), ultra-high-molecular-weight-polyethylene (UHMWPE) and UHMWPE+Bi. Ion implantation with Si+ and C+ was performed at energies of 30 keV with doses in the range 1013 – 1017 cm2. The results show that a PL enhancement (PLE) effect may occur for some polymer materials if proper implantation energy and doses are employed, the effect in the case of some polymer materials implanted with Si+ and C+ being considerable. While the effect is observed for all doses of C+ implanted in UHMWPE, PLE is only observed for the lowest dose of Si+ (D = 1×1015 cm−2) implanted in Teflon, the further dose increase resulting in PL quenching only, presumably due to processes of structural degradation The appearance of ultra-violet (UV) range PL in the case of Si+ implanted UHMWPE could be originating from the formation of Si-related new defect sites, but more data are needed to explore this effect further into the deeper UV range (λ<350 nm).

Electrochemical Reduction Synthesis of Photoluminescent Silicon Nanocrystals

An efficient synthesizing procedure of photoluminescent silicon nanocrystals is demonstrated using ultrasound assisted electrochemical octyltrichlorosilane reduction that produces alkyl terminated Si nanocrystals in a single step. The described procedure allows to make Si nanocrystals with octyl surface termination, is clean, relatively simple, and potentially scalable to industrial quantities. High resolution transmission electron microscopy, powder X-ray diffraction, UV-VIS absorbance, Fourier transform infra red spectroscopy and photoluminescence spectroscopy are employed to characterize the synthesized photoluminescent Si nanocrystals. Resulting octyl termination provides a stable passivation and could serve as a platform for further particle functionalization.

Electrochemical Reduction Synthesis of Photoluminescent Silicon Nanocrystals

An efficient synthesizing procedure of photoluminescent silicon nanocrystals is demonstrated by means of ultrasound assisted electrochemical octyltrichlorosilane reduction that produces octane terminated Si nanocrystals in a single step. The described procedure allows one to make Si nanocrystals with alkyl surface termination and is clean, relatively simple, and potentially scalable to industrial quantities. High resolution transmission electron microscopy, energy dispersive X-ray spectroscopy, UV-vis absorbance, Fourier transform infrared spectroscopy, and photoluminescence spectroscopy are employed to characterize the synthesized photoluminescent Si nanocrystals. Resulting octyl termination provides a stable passivation and could serve as a platform for further particle functionalization. Electrochemical chlorosilane reduction potentially could address the requirement for stable photoluminescent Si nanocrystals in diverse applications.

Light-emitting properties of amorphous Si:C:O:H layers fabricated by oxidation of carbon-rich a-Si:C:H films

Amorphous hydrogenated carbon-rich silicon–carbon alloy film (a-Si 0.3C 0.7:H) was deposited by reactive dc-magnetron sputtering of silicon target in argon–methane gas mixture. As-deposited film exhibits white photoluminescence at room temperature. After the deposition the samples were thermally annealed in dry Ar, wet Ar, or dry O 2 flow at 450 °C for 30 minutes that resulted in the enhancement of the photoluminescence intensity by a factor of about 5, 8 and 12 respectively. Spectral distribution of light emission was almost unchanged at the annealing in dry and wet argon while the oxidation in pure oxygen resulted in strong enhancement of a “blue” shoulder in the spectrum. EPR measurements at room temperature showed the decrease of spin concentration after thermal treatment in dry and wet argon and no EPR signal was detected after annealing in oxygen. FTIR and XPS measurements evidenced the formation of a-Si:O:C:H composite material after dry oxidation. Based on the measurements of photoluminescence in the temperature range 7–300 K it is suggested that light-emitting efficiency of a-Si 0.3C 0.7:H is determined by migration of the photo-excited carriers to non-radiative recombination centers. The physical mechanisms that can be involved in the strong enhancement of visible photoluminescence in Si:C:O:H layers are discussed.

CONTINUOUS-WAVE PHOTOLUMINESCENCE AND NANOSTRUCTURAL PROPERTIES OF POROUS SILICON

The photoluminescence (PL) emitted by porous silicon has been investigated by using the continuous tuneable UV Synchrotron Radiation Source. One sample was investigated for orange PL emission wavelength at temperatures 77–295 K. The PL peak is found to shift to higher frequency with decreasing temperature. Information about the nanostructure of porous silicon has been determined from PL and Extended X-ray Absorption Fine Structure (EXAFS), as well as from electron microscopy. In particular, the optical properties of silicon-based nanostructured materials, obtained from PL and photoluminescence excitation measurements, have been correlated with structural information from Si –K-edge EXAFS. Electron microscopy was used to study the relation between the nanostructure and PL of porous Si , and to investigate porous Si structure. Platelet Si and Si crystallites in porous Si layers were observed. The size of crystallites ranged from 4 to 6.5 nm. Diffraction patterns show these porous Si samples have a crystalline structure.