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Absence of free carriers in silicon nanocrystals grown from phosphorus- and boron-doped silicon-rich oxide and oxynitride
摘要： Phosphorus- and boron-doped silicon nanocrystals (Si NCs) embedded in silicon oxide matrix can be fabricated by plasma-enhanced chemical vapour deposition (PECVD). Conventionally, SiH4 and N2O are used as precursor gasses, which inevitably leads to the incorporation of ≈10 atom % nitrogen, rendering the matrix a silicon oxynitride. Alternatively, SiH4 and O2 can be used, which allows for completely N-free silicon oxide. In this work, we investigate the properties of B- and P-incorporating Si NCs embedded in pure silicon oxide compared to silicon oxynitride by atom probe tomography (APT), low-temperature photoluminescence (PL), transient transmission (TT), and current–voltage (I–V) measurements. The results clearly show that no free carriers, neither from P- nor from B-doping, exist in the Si NCs, although in some configurations charge carriers can be generated by electric field ionization. The absence of free carriers in Si NCs ≤5 nm in diameter despite the presence of P- or B-atoms has severe implications for future applications of conventional impurity doping of Si in sub-10 nm technology nodes.
关键词： photoluminescence,silicon nanocrystals,transient transmission,doping,atom probe tomography
更新于2025-09-23 15:23:52
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Changes of the absorption cross section of Si nanocrystals with temperature and distance
摘要： The absorption cross section (ACS) of silicon nanocrystals (Si NCs) in single-layer and multilayer structures with variable thickness of oxide barriers is determined via a photoluminescence (PL) modulation technique that is based on the analysis of excitation intensity-dependent PL kinetics under modulated pumping. We clearly demonstrate that roughly doubling the barrier thickness (from ca. 1 to 2.2 nm) induces a decrease of the ACS by a factor of 1.5. An optimum separation barrier thickness of ca. 1.6 nm is calculated to maximize the PL intensity yield. This large variation of ACS values with barrier thickness is attributed to a modulation of either defect population states or of the efficiency of energy transfer between confined NC layers. An exponential decrease of the ACS with decreasing temperature down to 120 K can be explained by smaller occupation number of phonons and expansion of the band gap of Si NCs at low temperatures. This study clearly shows that the ACS of Si NCs cannot be considered as independent on experimental conditions and sample parameters.
关键词： silicon nanocrystals,average lifetime,absorption cross section,photoluminescence decay,nanocrystal distance
更新于2025-09-23 15:22:29
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Silicon nanocrystal hybrid photovoltaic devices for indoor light energy harvesting
摘要： Silicon nanocrystals (SiNCs) featuring size-dependent novel optical and electrical properties have been widely employed for various functional devices. We have demonstrated SiNC-based hybrid photovoltaics (SiNC-HPVs) and proposed several approaches for performance promotion. Recently, owing to the superiorities such as low power operation, high portability, and designability, organic photovoltaics (OPVs) have been extensively studied for their potential indoor applications as power sources. SiNCs exhibit strong light absorption below 450 nm, which is capable of sufficient photocurrent generation under UV irradiation. Therefore, SiNC-HPVs are expected to be preferably used for energy harvesting systems in indoor applications because an indoor light source consists of a shorter wavelength component below 500 nm than solar light. We successfully demonstrated SiNC-HPVs with a PCE as high as 9.7%, corresponding to the output power density of 34.0 mW cm?2 under standard indoor light irradiation (1000 lx). In addition, we have found that SiNC defects working as electron traps influence the electrical properties of SiNCs substantially, a thermal annealing process was conducted towards the suppression of defects and the improvement of the SiNC-HPVs performance.
关键词： Silicon nanocrystals,Power conversion efficiency,Indoor light energy harvesting,Thermal annealing,Hybrid photovoltaics
更新于2025-09-23 15:21:01
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Controlled Surface for Enhanced Luminescence Quantum Yields of Silicon Nanocrystals; 蛍光シリコン粉末の機能増強を導く表面制御に関する研究;
摘要： In the current review paper, we provide the experimental evidences for the controlled structure of diamond cubic silicon nanocrystals (SiNCs) which enhances their photoluminescence quantum yields (PLQYs). Hydrogen-terminated Si provides a basic surface for further modification. Their enhancement was performed by a simple ligand exchange between the hydrogen atoms and hydrocarbon chains. On the basis of the systematic study on temperature dependence of PL properties along with relaxation dynamics, a long-accepted mechanism for enhancing absolute PL was recently revised. Specifically, combination of PL spectroscopic measurement from cryogenic to room temperature with structural characterization allows us to link the enhanced PLQYs with the notable difference in surface structure. The hydride-terminated surface suffers from the presence of a large amount of nonradiative relaxation channels whereas the passivation with alkyl monolayers suppresses the creation of the nonradiative relaxation channels to yield the high PLQY. This anchoring effect was responsible for the PLQYs as high as 56%. Tunability of PL bands was achieved in the wavelength ranging between 590 nm and 1064 nm. Next, the review considers the use of the highly emitting SiNCs for optoelectronic and biophotonic applications. The tunable light emitting diodes in which SiNCs serve as active layers are demonstrated. Si exhibits a high chemical affinity to covalent linkages with carbon, oxygen, and nitrogen, thereby producing almost unlimited variations in organic–Si architectures hybridized at the molecular level. Therefore, biomedical applications of SiNCs are attractive. Details of the biophotonic applications are not described in this review, but functional near-IR (NIR) emitting nanoparticles of SiNCs of narrow PL spectra having no long emission tails, continuously tunable over the 700–1000 nm window where the light absorption of water and the tissues including hemoglobin is minimal have a potential to become one of nontoxic biomarkers that is available in-vivo study. Finally, we provide perspective on the overall current status, challenges and potentials for this research field in near future.
关键词： Anchor effect,Silicon nanocrystals,Photoluminescence,Light emitting diode
更新于2025-09-12 10:27:22
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Structural characterization determination of silicon nanocrystals embedded in amorphous silicon nitride matrix from the effect of the light scattering
摘要： In this work, we will study the elastic and inelastic light scattering by the silicon nanocrystals (Si-nc) embedded in amorphous silicon nitride matrix. Indeed, the photons are subjected to several modifications in terms of intensity, direction and wavelength when they interact with Si-ncs. The reflectance combined with photoluminescence (PL) and Raman spectroscopy are a very sensitive tool for probing the scattering light. Results show that the observed shift of the experimental PL peaks is attributed to the Raman scattering and the PL broadening peaks to the Rayleigh scattering. A novel method allowed the determination of both the core and the surface bond lengths of Si-nc was reported. The decrease of the Raman shift observed in structures containing Si-ncs is mainly due to the Si-nc curved surface, and it reflects the presence of silicon dangling bonds at the Si-nc interfaces.
关键词： Rayleigh scattering,Silicon nanocrystals,Silicon dangling bond,Raman scattering,Bond length,Silicon nanocrystal surface
更新于2025-09-10 09:29:36
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Mixed Surface Chemistry: An Approach to Highly Luminescent Biocompatible Amphiphilic Silicon Nanocrystals.
摘要： Amphiphilic nanoparticles (AP-NPs) are attractive for many far-reaching applications in diverse sectors. Amphiphilic silicon nanocrystals (AP-SiNCs) are particularly promising for luminescence-based bioimaging, biosensing, and drug delivery due to their size- and surface chemistry-dependent photoluminescence, high photoluminescence quantum yield, long-term photostability, and robustness to bioconjugation. Numerous studies demonstrated the synthesis of high quality SiNCs that are compatible with organic solvents. However, preparing water-soluble SiNCs while maintaining their attractive PL properties is very challenging and to date, only one report of blue-emitting amphiphilic silicon nanocrystals (AP-SiNCs) has appeared. This report outlines a straightforward one-step thermal hydrosilylation approach that affords AP-SiNCs soluble in aqueous media in high concentrations (i.e., 14.4 mg/mL silicon core-based), exhibit bright long-lived photoluminescence in the red/near-infrared spectral region, are biocompatible, and present bio-conjugable surface groups.
关键词： Drug delivery,Photoluminescence,Silicon nanocrystals,Biosensing,Bioimaging,Amphiphilic nanoparticles
更新于2025-09-09 09:28:46
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The peculiarities of structural and optical properties of HfO2-based films co-doped with silicon and erbium
摘要： The effect of deposition conditions and further annealing treatment on microstructure and optical properties of (Si,Er)-codoped HfO2 thin films is investigated. The films are grown on silicon substrates by RF magnetron co-sputtering of Si and erbium oxide pellets on a HfO2 target. As-deposited and annealed samples are examined by means of spectroscopic ellipsometry, Fourier transform infrared spectroscopy and photoluminescence method. It is demonstrated that the variation of RF power density allows monitoring the dopant content. An annealing of the samples at 800-1100°C for 10-60 min in nitrogen atmosphere results in the phase separation and the formation of HfO2, SiO2 and pure silicon phases. The films annealed at 900-950°C demonstrate the red luminescence that is ascribed to the carrier recombination in Si nanocrystals. Annealing at higher temperatures causes an enhancement of rare-earth luminescence under non-resonant excitation providing an additional argument toward the formation of silicon nanoclusters. The mechanism of the excitation of Er ions is found to be similar to that of Si-rich-SiO2 films doped with rare-earths. The Si nanocrystals are considered as the main sensitizer at visible excitation while the energy transfer from host defects dominates at ultraviolet-deep blue illumination.
关键词： erbium,hafnium oxide,silicon,nanocrystals,photoluminescence
更新于2025-09-09 09:28:46