CO2 detection with CNx thin films deposited on porous silicon

In recent years, porous silicon (PSi) has attracted a great deal of attention for sensing applications. However, the high reactivity of PSi surfaces causes serious problems of stability. In this work, we developed new thin films that can serve as stabilizer of PSi for CO₂ gas sensors development. PSi surface was coated with carbon nitride (CN_x) film which is one of the most important interfering to stabilize the PSi layer. CN_x film was deposited by pulsed laser ablation. The effect of CO₂ gas on the sensor response was investigated for different polarization voltages. The electrical properties of (Al/CN_x/PSi/Si) structure were modified in the presence of the gas. The device shows a high sensitivity against CO₂ gas. Furthermore, the current variation of the sensor as a function of time has been investigated. The results show that the Al/CN_x/PSi/Si structure becomes stable after the first two weeks.     

Properties of discontinuous gold thin films deposited on a silicon substrate

Experimental results on the dependence on deposition conditions of the electrical resistance and gauge factor of discontinuous gold films in the vicinity of the percolation threshold are reported. The three-dimensional nature of the films is emphasized. The gauge factor reveals anomalous behaviour.     

Investigation of polarization anisotropy in individual porous silicon nanoparticles

Polarization anisotropy is investigated in single porous silicon nanoparticles containing multiple chromophores. Two forms of nanoparticle samples are studied; low current density (LCD) and high current density (HCD). Photoluminescence measurements reveal that LCD samples exhibit red-shifted spectra and HCD particles display a blue-shifted spectrum. We utilize single molecule spectroscopy to detect the polarization effects of spatially isolated individual nanoparticles, and show that LCD nanoparticles demonstrate strong polarization anisotropy, whereas a dynamic polarization response is collected from HCD nanoparticles.     

金纳米颗粒增强富硅氮化硅发光特性的研究

采用时域有限差分(FDTD)方法,对Au纳米颗粒的尺寸和形貌对于其光学特性的影响进行了系统的理论研究。通过采用等离子体增强化学气相沉积(PECVD)、晶化处理、电子束蒸发和高温退火等工艺,制备基于局域表面等离子共振(LSPR)效应的富硅氮化硅发光芯片。利用拉曼光谱仪、扫描电子显微镜(SEM)、奥林巴斯显微镜等对不同结构Au纳米颗粒富硅氮化硅发光器件的特性进行了表征。研究表明,通过对Au纳米颗粒的大小、形状和分布合理优化,富硅氮化硅芯片的发光强度在570nm波长附近提升了7倍,增强峰的位置红移了10nm。     

Photoconductivity of organic polymer films doped with porous silicon nanoparticles and ionic polymethine dyes

Features of electrical conductivity and photoconductivity of polyvinylbutyral films containing porous silicon nanoparticles and similar films doped with cationic and anionic polymethine dyes are studied. Sensitization of the photoelectric effect by dyes with different ionicities in films is explained by the possible photogeneration of holes and electrons from dye molecules and the intrinsic bipolar conductivity of porous silicon nanoparticles. It is assumed that the electronic conductivity in porous silicon nanoparticles is higher in comparison with p-type conductivity.     

Effect of annealing temperature on the copper nanoparticles deposited on the silicon nanoporous pillar array

Copper/silicon nanocomposite system (Cu/Si-NPA) is prepared by immersion plating Cu nanoparticles on silicon nanoporous pillar array (Si-NPA). The Cu/Si-NPA samples are heated under nitrogen for 2 h at elevated temperatures of 400 °C, 600 °C, and 800 °C. The morphological changes of Cu nanoparticles before and after heat treatments are characterized by SEM. The crystallinity and the average size of Cu nanoparticles before and after heat treatments are studied by XRD. The results show that two possible mechanisms, Ostwald ripening, and particle migration and coalescence, are believed to be responsible for the ripening of annealed Cu nanoparticles at different annealing temperatures.     

Enhancement of photoluminescence and raman scattering in one-dimensional photonic crystals based on porous silicon

In porous-silicon-based multilayered structures that exhibit the properties of one-dimensional photonic crystals, an increase in the photoluminescence and Raman scattering intensities is observed upon optical excitation at the wavelength 1.064 μm. When the excitation wavelength falls within the edge of the photonic band gap of the structures, a multiple increase (by a factor larger than 400) in the efficiency of Raman scattering is detected. The effect is attributed to partial localization of excitation light and, correspondingly, to the much longer time of interaction of light with the material in the structures.     

Photoresponse and electroluminescence of silicon-〈porous silicon〉-〈chemically deposited metal〉 structures

Photoelectric and electroluminescent properties of silicon-〈porous silicon〉 structures with chemically deposited metal contacts were investigated. The large specific surface area of the contact and selective metal deposition only on the macrocrystalline elements of the structure provide better photoelectric performance of the photodiodes compared to the structures with evaporated contacts, especially in the short-wavelength spectral range. The obtained electroluminescence spectra are explained by metal-silicon barrier properties under forward bias and by double carrier injection into nanocrystallites under reverse bias.     

Photoluminescence enhancement of porous silicon prepared with ammonium sulfide pre-treated silicon

As-grown porous silicon prepared with ammonium sulfide pre-treated silicon show stable photoluminescence characteristics due to high Si–N/PS interface quality and less damage PS with Si–N passivation. After aging in air for 6 months, it shows much stronger photoluminescence intensity and stable wavelength due to higher Si–ON/PS interface quality and less damage of PS with Si–O–N passivation from the oxidation of Si–N.     

超临界干燥多孔硅的光致发光

对两种不同条件下制备的多孔硅进行了红外透射光谱测量，并对超临界干燥和自然干燥条件下的光致发光光谱进行了对比测量。用高分辨率透射电镜对其结构进行了观察，研究表明多孔硅的发光机理与其制备条件有关。     

激光沉积硅膜的形成和微结构

前言 现代半导代技术中~[1]沉积薄膜的方法起着重要作用。激光可以为薄膜的沉积极提供一种独特的热源和光源，可以引起热或光化学作用。激光方法能够减少或消除其他方法的问题~[2]，能够沉积出高质量的薄膜，这种技术的主要优点是在沉积过程中可选择空间，薄膜生产可以限制在基板一个很小的点上。当然大面积沉积也是可能的。大的冷区同小的热区相比的情况有效地防止气相反应和基板还原。     

Structure and properties of porous silicon obtained by photoanodization

The results of an investigation of layers of porous silicon (PS), which was obtained by electrochemical etching of p-Si under different illumination conditions — natural light, incandescent light, and light from a mercury lamp with and without a filter — are reported. The structure of the layers was studied by double-crystal x-ray diffractometry, the composition was monitored by means of the IR absorption spectra, and the radiative properties were monitored according to the photoluminescence (PL) spectra. It was established that electrochemical etching under illumination produces PS with a higher porosity and more intense PL whose maximum is shifted into the short-wavelength region. These changes are accompanied by a large disordering of the structure and an increase in the oxygen content in the layer. It is concluded that illumination accelerates the chemical interaction of PS with the electrolyte due to oxidation. High-porosity porous silicon stored in air exhibits quenching of PL. Conversely, PL is excited in layers with a lower porosity. Aging of PS is characterized by an increase in the microdeformation of the layers, a decrease in the crystallite sizes with a partial loss of coherence between the crystallites and the substrate, and an increase in the fraction of the amorphous phase. Fiz. Tekh. Poluprovodn. 31, 1261–1268 (October 1997)     

利用ICPCVD方法在GaN上沉积氧化硅薄膜的特性

使用感应耦合等离子体化学气相沉积(Inductively coupled plasma chemical vapor deposition,ICPCVD)方法在GaN上沉积SiOx薄膜,生长参数中采用不同RF功率,研究RF功率对薄膜物理性能和电学性能的影响.结果发现,随着RF功率增大,薄膜应力增大,表面粗糙度减小,薄膜致密度增大.选择最优的RF功率参数,制作了SiOx/nGaN金属-绝缘体-半导体(metal-insulator-semiconductor,MIS)器件,结果得到薄膜漏电流密度在外加偏压为90V时小于1×10-7A/cm2,SiOx/n-GaN界面态密度为2.4×1010eV-1cm-2.表明利用ICPCVD低温沉积的SiOx-GaN界面态密度低,薄膜绝缘性能良好.     

Enhancement of silicon solar cells by downshifting with Eu and Tb coordination complexes

Luminescent lanthanide‐doped oxides, nanoparticles, nanocrystals, and coordination complexes are major tools in the fields of optical and laser materials, telecommunications, medical imaging, and fluoroimmunoassays. In particular, coordination complexes are efficient energy converters with high photostability, large ligand‐induced Stokes shifts, and tunable excitation and emission spectra. However, their application as light downshifting materials for solar cells has not yet been widely explored. This third generation solar cell concept enables to increase the efficiency of standard solar cells—such as Si or copper indium gallium (di)selenide (CIGS)—that have low performance for ultraviolet photons. The incorporation of such a converter in solar module encapsulants can provide a cheap and effective way to integrate photon conversion. Here, encapsulants functionalised by photon downshifting coordination complexes have been spin‐coated on silicon solar cells. For all the coordination complexes, an increase of the spectral response of the solar cells is observed in the ultraviolet region. In the best case, a relative increase of 8% of the conversion efficiency of the solar cell is observed. Copyright © 2016 John Wiley & Sons, Ltd.     

Relaxation spectra of photoluminescence from porous silicon obtained by chemical etching of laser-modified silicon

The distinctive features of time-resolved photoluminescence spectra of porous silicon created by chemical etching of single-crystal silicon subjected to modification by laser light has been investigated. Two bands were seen upon examination of the amplitude spectra: a band with a maximum at a wavelength (λ _max⋍530 nm) and a band with λ _max⋍420 nm and twice the intensity of the first. The relaxation curves are characterized by two sets of times: τ ₁<2×10⁻⁸ s and 2×10⁻⁸ s<τ ₂×10⁻⁴ s in the spectral ranges 420–700 nm and 500–850 nm, respectively. Upon increasing the energy density of the laser irradiation from ∼10 to ∼40 J·cm⁻², the intensity of the photoluminescence and the contribution of the fast component increased as well. The difference in the photoluminescence spectra compared to the spectra of layers of porous silicon obtained by electrochemical etching is attributable to a shift in the distribution of nanocrystallite sizes toward smaller sizes, which leads to an increase in the area of the Si/SiO_x surface that separates the phases. Although our results can be explained within the framework of a quantum-well model, we do not rule out the contribution of local centers at the Si/SiO_x phase boundary. The slow component of the relaxation is approximated by a “stretched” exponential. It is assumed that the slow component is controlled by the rate at which photocarriers leave the quantum-well nanocrystallites by tunneling through the Si/SiO_x barrier. Fiz. Tekh. Poluprovodn. 31, 6–10 (January 1997)     

Bulk and surface passivation of silicon solar cells accomplished by silicon nitride deposited on industrial scale by microwave PECVD

Bulk and surface passivation by silicon nitride has become an indispensable element in industrial production of multicrystalline silicon (mc‐Si) solar cells. Microwave PECVD is a very effective method for high‐throughput deposition of silicon nitride layers with the required properties for bulk and surface passivation. In this paper an analysis is presented of the relation between deposition parameters of microwave PECVD and material properties of silicon nitride. By tuning the process conditions (substrate temperature, gas flows, working pressure) we have been able to fabricate silicon nitride layers which fulfill almost ideally the four major requirements for mc‐Si solar cells: (1) good anti‐reflection coating (refractive index tunable between 2·0 and 2·3); (2) good surface passivation on p‐type FZ wafers (S_eff<30 cm/s); (3) good bulk passivation (improvement of IQE at 1000 nm by 30% after short thermal anneal); (4) long‐term stability (no observable degradation after several years of exposure to sunlight). By implementing this silicon nitride deposition in an inline production process of mc‐Si solar cells we have been able to produce cells with an efficiency of 16·5%. Finally, we established that the continuous deposition process could be maintained for at least 20 h without interruption for maintenance. On this timescale we did not observe any significant changes in layer properties or cell properties. This shows the robustness of microwave PECVD for industrial production. Copyright © 2005 John Wiley & Sons, Ltd.     

晶种法可控制备硫普罗宁包覆的大尺寸金纳米颗粒

该实验采用15 nm的金纳米颗粒作为晶种,使用晶种生长法合成尺寸为50 nm和100 nm的金纳米颗粒,通过表面配体交换法得到表面包覆硫普罗宁的大尺寸金纳米颗粒。该法制备过程简单可控,得到的金纳米颗粒尺寸分布较窄,单分散性良好,为金纳米颗粒在其他领域的研究及应用提供了良好的前提条件。     

多孔硅制备中醇对形貌的影响

实验研究了无光照情况下多孔硅制备中不同单羟基正醇对形貌的影响。实验结果表明,随着醇碳链的增长,多孔硅孔密度减小,枝杈变长,枝杈的尖端变得尖锐。在孔的生长过程中,十字枝杈首先沿着晶格方向快速生长,然后晶格方向的生长速率减小,而非晶格方向则持续生长直到空穴耗尽。本实验增进了对硅溶解动力学中醇作用机理的理解。     

Absorption enhancement of silicon solar cell with Ag nanoparticles by surface plasmons resonance

The absorption enhancements of silicon layer in silicon solar cells with three kinds of Ag nanoparticles including sphere, cylinder and cuboid are studied by the finite difference time domain （FDTD） method, respectively. The results show that the light absorption of silicon is significantly improved due to the localized surface plasmon （LSP） reso- nance. The relations of the absorption enhancement with the parameters of nanoparticles are thoroughly analyzed. The optimal absorption enhancement can be achieved by adjusting the relevant parameters. Among the three types of Ag nanoparticles, i.e., sphere, cylinder and cuboid, the silicon with the cubical Ag nanopaticles shows the most efficient absorption enhancement at optimal conditions, its maximum absorption enhancement factor is 1.35, and that with the spherical Ag nanopaticles gets the lowest absorption enhancement. The work is useful for the further theoretical study and design for the plasmonic thin-film solar cell.