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Tailoring Photoluminescence from Si-Based Nanocrystals Prepared by Pulsed Laser Ablation in He-N2 Gas Mixtures
摘要： Using methods of pulsed laser ablation from a silicon target in helium (He)-nitrogen (N2) gas mixtures maintained at reduced pressures (0.5–5 Torr), we fabricated substrate-supported silicon (Si) nanocrystal-based ?lms exhibiting a strong photoluminescence (PL) emission, which depended on the He/N2 ratio. We show that, in the case of ablation in pure He gas, Si nanocrystals exhibit PL bands centered in the “red - near infrared” (maximum at 760 nm) and “green” (centered at 550 nm) spectral regions, which can be attributed to quantum-con?ned excitonic states in small Si nanocrystals and to local electronic states in amorphous silicon suboxide (a-SiOx) coating, respectively, while the addition of N2 leads to the generation of an intense “green-yellow” PL band centered at 580 nm. The origin of the latter band is attributed to a radiative recombination in amorphous oxynitride (a-SiNxOy) coating of Si nanocrystals. PL transients of Si nanocrystals with SiOx and a-SiNxOy coatings demonstrate nonexponential decays in the micro- and submicrosecond time scales with rates depending on nitrogen content in the mixture. After milling by ultrasound and dispersing in water, Si nanocrystals can be used as e?cient non-toxic markers for bioimaging, while the observed spectral tailoring e?ect makes possible an adjustment of the PL emission of such markers to a concrete bioimaging task.
关键词： pulsed laser ablation in gases,pulsed laser deposition,silicon quantum dots,bioimaging,silicon nanoparticles,quantum con?nement,photoluminescence,silicon oxynitride
更新于2025-09-19 17:13:59
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Enhanced surface passivation of predictable quantum efficient detectors by silicon nitride and silicon oxynitride/silicon nitride stack
摘要： In this paper, we investigate three different passivating films for use in predictable quantum efficient detectors: two monolayer films of SiNx with different compositions and one double-layer stack of SiNxOy capped with SiNx, all deposited on very high resistivity silicon substrates. In addition to the conventional characterization methods, we also utilize the novel method of photoluminescence imaging under applied bias (PL-V) and high voltage soaking to modulate the fixed charge density Qf in the layers. All films exhibit very good passivating properties after deposition and annealing, with the oxynitride stack providing the best passivation, resulting in an effective carrier lifetime close to 20 ms. This value is explained by a relatively high fixed charge density of Qf = 1.12 × 1012 cm?2 and low interface defect density (S0,n = 6.0 × 102 cm/s), giving a chemical passivation which is an order of magnitude better than the investigated nitrides. Both nitride films were readily charged by voltage soaking, increasing the effective carrier lifetime by about 20%. Based on the passivating properties, photodetector device simulations predict that self-induced photodiodes made with any of these passivation layers will have an internal quantum deficiency well below 1 ppm for selected wavelengths at room temperature, and all the investigated materials are thus good candidates for use as passivating layers in such photodiodes.
关键词： photoluminescence imaging,surface passivation,silicon nitride,high voltage soaking,predictable quantum efficient detectors,silicon oxynitride
更新于2025-09-09 09:28:46
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Measurements of Microstructural, Chemical, Optical, and Electrical Properties of Silicon-Oxygen-Nitrogen Films Prepared by Plasma-Enhanced Atomic Layer Deposition
摘要： In this study, silicon nitride (SiNx) thin films with different oxygen concentration (i.e., SiON film) were precisely deposited by plasma enhanced atomic layer deposition on Si (100) substrates. Thus, the effect of oxygen concentration on film properties is able to be comparatively studied and various valuable results are obtained. In detail, x-ray reflectivity, x-ray photoelectron spectroscopy, atomic force microscopy, and spectroscopic ellipsometry are used to systematically characterize the microstructural, optical, and electrical properties of SiON film. The experimental results indicate that the surface roughness increases from 0.13 to 0.2 nm as the oxygen concentration decreases. The refractive index of the SiON film reveals an increase from 1.55 to 1.86 with decreasing oxygen concentration. Accordingly, the band-gap energy of these films determined by oxygen 1s-peak analysis decreases from 6.2 to 4.8 eV. Moreover, the I-V tests demonstrate that the film exhibits lower leakage current and better insulation for higher oxygen concentration in film. These results indicate that oxygen affects microstructural, optical, and electrical properties of the prepared SiNx film.
关键词： silicon nitride,silicon oxynitride,oxygen contamination,optical properties,plasma enhanced atomic layer deposition
更新于2025-09-04 15:30:14