纳米Si-SiOx和Si-SiNx复合薄膜的低温制备及其发光特性

用等离子体增强化学气相沉积法在低温（低于50℃）衬底上沉积Si-SiOx和Si-SiNx复合薄膜,可得到平均颗粒尺寸小至3nm的高密度（最高可达4.0×1012cm-2）纳米硅复合薄膜.500℃快速退火后,这种复 合薄膜显现出优异的可见光全波段光致发光特性.通过比较相同条件下所制备的纳米Si-SiOx和Si-SiNx复合薄膜的光致发光效率,发现纳米Si-SiNx具有更为优异 的光致发光效率,这一点在可见光短波区表现得尤为显著. 关键词： 等离子体增强化学气相沉积 冷衬底 硅纳米颗粒 光致发光     

纳米Si-SiO_x和Si-SiN_x复合薄膜的低温制备及其发光特性

用等离子体增强化学气相沉积法在低温 (低于 5 0℃ )衬底上沉积Si SiOx 和Si SiNx 复合薄膜 ,可得到平均颗粒尺寸小至 3nm的高密度 (最高可达 4 0× 10 1 2 cm- 2 )纳米硅复合薄膜 .5 0 0℃快速退火后 ,这种复合薄膜显现出优异的可见光全波段光致发光特性 .通过比较相同条件下所制备的纳米Si SiOx 和Si SiNx 复合薄膜的光致发光效率 ,发现纳米Si SiNx 具有更为优异的光致发光效率 ,这一点在可见光短波区表现得尤为显著     

Specific features and mechanisms of photoluminescence of nanostructured silicon carbide films grown on silicon in vacuum

The light-emitting properties of cubic silicon carbide films grown by vacuum vapor phase epitaxy on Si(100) and Si(111) substrates under conditions of decreased growth temperatures (T _gr ∼ 900–700°C) have been discussed. Structural investigations have revealed a nanocrystalline structure and, simultaneously, a homogeneity of the phase composition of the grown 3C-SiC films. Photoluminescence spectra of these structures under excitation of the electronic subsystem by a helium-cadmium laser (λ_excit = 325 nm) are characterized by a rather intense luminescence band with the maximum shifted toward the ultraviolet (∼3 eV) region of the spectral range. It has been found that the integral curve of photoluminescence at low temperatures of measurements is split into a set of Lorentzian components. The correlation between these components and the specific features of the crystal structure of the grown silicon carbide layers has been analyzed.     

Dislocation-related photoluminescence in silicon

Photoluminescence is studied in silicon, deformed in a well-defined and reproducible way. Usual deformation conditions (high temperature, low stress) result in sharp spectra of the D1 through D4 lines as recently described in the literature. New lines D5 and D6 emerge for predeformation as above and subsequent low-temperature, high-stress deformation. Another new sharp line, D12, is observed when both the familiar and the novel lines appear simultaneously. Annealing for 1 h atT _A 300 °C causes all new lines to disappear and the D1–D4 spectra to reappear. Quantitative annealing and TEM micrographs suggest that D5 is related to straight dislocations and D6 to stacking faults, whereas D1–D4 are due to relaxed dislocations. Photoluminescence under uniaxial stress shows that D1/D2 originate in tetragonal defects with random orientation relative to 100 directions, whereas D6 stems from triclinic centers, preferentially oriented — as are the D3/D4 centers. We conclude that the D3/D4 and the D5 and D6 defects are closely related, whereas the independent D1/D2 centers might be deformation-produced point defects in the strain region of dislocations.     

Modulation effect of microstructures in silicon-rich oxide matrix on photoluminescence from silicon nanoclusters prepared by different fabrication techniques

The modulation effect of microstructures on photoluminescence (PL) properties of silicon nanoclusters (Si NCs) in silicon-rich oxide (SRO) matrix prepared by electron-beam evaporation (EBE) and magnetron sputtering (MS) is investigated. A loose and porous microstructure is obtained from the SRO film prepared by EBE, while compact microstructure is acquired from that prepared by MS. The Si NCs with high density and good quality are formed in the SRO film prepared by EBE, and preferable PL performance of Si NCs is achieved in the EBE film with loose and porous microstructure. In contrast, the density and quality of Si NCs in the compact SRO film are suppressed and the PL properties are deteriorated due to the volumetric mismatching during the precipitation procedure of Si NCs. Optimization of the microstructures in SRO films should be made to reduce the volumetric mismatching and improve the PL properties of Si NCs.     

Dielectric spectroscopy investigations of nanostructured silicon

Dielectric spectroscopy measurements were performed on planar silicon nanostructures buried within a crystalline Si that form a nanoscale Si-layered system. An insight into the specific behavior of the free-carrier population confined in the surface potential well was then made possible. It was found that the presence or the absence of the SiO₂ passivation modifies considerably relaxation responses of the studied structures. A clear differentiation of two dielectric responses: from the same sample with and without electronic passivation allowed determination of the conduction behavior in the surface c-Si delimited by the nanoscale Si-layered system. The sample with a 100 nm thick SiO₂ layer (and an excellent quality of the SiO₂/c-Si interface) exhibits a fractional power-law dielectric response, corresponding clearly to the generalized Mittag–Leffler pattern. Simultaneously, the dielectric response of a bare sample (after the total RIE of the previously deposited SiO₂ layer, about 10 nm native SiO₂ layer and poor quality of the SiO₂/c-Si interface) is dominated by the conductivity term.     

多孔硅的时间延迟光谱

利用时间延迟光谱技术测量了多孔硅的发光光谱. 实验结果表明,多孔硅的发光是复杂的动力学发光弛豫过程,时间延迟光谱测量技术在研究复杂动力学发光过程方面比稳态光谱测量方法更有效.     

Comparative investigation of photoluminescence of silicon wire structures and silicon oxide films

Photoluminescence spectra and their dependence on temperature as well as Raman scattering spectra and Atomic Force Microscopy investigations have been used to study the peculiarities of the red photoluminescence band in low-dimensional Si structures, such as porous silicon and silicon oxide films. It has been shown that the red photoluminescence band of porous silicon is complex and can be decomposed into two elementary bands. It was discovered that elementary band intensities depend very much on surface morphology of porous silicon. The same positions of the photoluminescence bands are also observed in silicon oxide films for different oxide composition. Comparative investigation of the PL temperature dependences in porous silicon and silicon oxide films indicates that silicon-oxide defect related mechanisms of some elementary photoluminescence bands are involved.     

Enhanced photoluminescence in grooved silicon microstructures

Grooved silicon structures formed by anisotropic chemical etching of crystalline silicon (c-Si) wafers in alkaline solution and composed by c-Si walls and voids (grooves) with thicknesses of several micrometers were found to exhibit efficient photoluminescence after excitation with laser radiation at 1.06 μm. The photoluminescence emission which originates from the interband radiative recombination of charge carriers in c-Si walls was represented by a broad spectral band centered at 1.1 eV. Independently on the polarization direction of the excitation light the photoluminescence of grooved silicon structures was partially linear-polarized with the polarization degree of 0.15–0.24 along c-Si walls and the photoluminescence intensity was strongly enhanced in comparison with that of c-Si substrate. These experimental observations are explained by considering an enhancement of the photoluminescence excitation due to both partial light localization in c-Si walls and a low rate of the non-radiative recombination at surface defects on c-Si walls. The defect density could be modified by additional chemical treatment or thermal annealing, which resulted in significant changes of the photoluminescence intensity of the grooved Si structures. The obtained results are discussed in view of possible applications of grooved Si in optoelectronics and molecular sensorics.     

Synthesis and photoluminescence studies of silicon nanoparticles embedded in silicon compound films

High-density silicon nanoparticles with well-controlled sizes were grown onto cold substrates in amorphous SiN_x and SiC matrices by plasma-enhanced chemical vapor deposition. Strong, tunable photoluminescence across the whole visible light range has been measured at room temperature from such samples without invoking any post-treatment, and the spectral features can find a qualitative explanation in the framework of quantum confinement effect. Moreover, the decay time was for the first time brought down to within one nanosecond. These excellent features make the silicon nanostructures discussed here very promising candidates for light-emitting units in photonic and optoelectronic applications.     

Giant birefringence in anisotropically nanostructured silicon

We performed a study of the in-plane birefringence of anisotropically nanostructured Si layers, which exhibit a greater difference in the main value of the anisotropic refractive index than that of natural birefringent crystals. The anisotropy parameters were found to be strongly dependent on the typical size of the Si nanowires used to assemble the layers. This finding opens the possibility of an application of birefringent Si retarders to a wide spectral range for control of the polarization state of light.     

Synthesis and photoluminescence studies of silicon nanoparticles embedded in silicon compound films

High-density silicon nanoparticles with well-controlled sizes were grown onto cold substrates in amorphous SiN _x and SiC matrices by plasma-enhanced chemical vapor deposition. Strong, tunable photoluminescence across the whole visible light range has been measured at room temperature from such samples without invoking any post-treatment, and the spectral features can find a qualitative explanation in the framework of quantum confinement effect. Moreover, the decay time was for the first time brought down to within one nanosecond. These excellent features make the silicon nanostructures discussed here very promising candidates for light-emitting units in photonic and optoelectronic applications.      

Nanocrystal-size-sensitive third-harmonic generation in nanostructured silicon

Third-harmonic generation (THG) in reflection geometry was studied in nanostructured silicon layers grown by electrochemical porosifying of p-type (110) silicon substrates. An order of magnitude enhancement of the THG efficiency compared to crystalline silicon (c-Si) was observed for the samples prepared on a highly doped substrate, whereas for the samples grown on a low-doped substrate the THG was much less efficient than for c-Si. The finding is discussed in terms of fluctuations of the electric field of the pump-laser irradiation in the layers of anisotropically distributed silicon nanocrystals. Received: 26 July 2002 / Revised version: 9 January 2003 / Published online: 3 April 2003 RID="*" ID="*"Corresponding author. Fax: +7-95/939-1566, E-mail: leo@vega.phys.msu.su     

Instability of the photoluminescence of porous silicon

Results of studies of the photoluminescence of porous silicon with different prehistories have revealed the mechanism and nature of the instability of the luminescence properties of freshly prepared samples. It was established that the initial quenching and subsequent rise of the photoluminescence is attributable to the intermediate formation of silicon monoxide (photoluminescence degradation) and subsequent additional oxidation to form SiO₂ (photoluminescence rise). Ultraviolet laser irradiation accelerates this process by a factor of 200–250 compared with passive storage of the samples in air. Plasma-chemical treatment in an oxygen environment merely results in a subsequent rise in the photoluminescence as a result of the formation of monoxide on the porous silicon surface. A kinetic model is proposed for this process. Zh. Tekh. Fiz. 69, 135–137 (June 1999)     

Roles of interfaces in nanostructured silicon luminescence

The increasing interest in photonics in the field of communication has led to intense research work on silicon based nanostructures showing efficient photoluminescence. The present paper reports photoluminescence measurements obtained at room temperature in silicon-rich-silica-silica multilayers grown by reactive magnetron sputtering. The silicon nanograin size is controlled via the silicon layer thickness which can be monitored with high accuracy. We aim to develop a comprehensive understanding of the combined roles played by the quantum confinement effect through the silicon grain size and the existence of an interfacial region between the grain and the surrounding silica matrix. Two bands of photoluminescence are displayed in the 600 nm-900 nm range and correspond to the bands previously observed at 2 K. Their origin is demonstrated through a model based on the solution of the Schrödinger equation of the exciton wavefunction in a one-dimension geometry corresponding to the growth direction of the multilayers. The silicon layer as well as the Si-SiO₂ interface thicknesses are the key parameters of the photoluminescence features.Received: 6 April 2004, Published online: 21 October 2004PACS: 78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures - 73.21.Ac Multilayers - 71.23.An Theories and models; localized states     

Enhanced photoluminescence of conjugated polymer thin films on nanostructured silver

Photoluminescence of a conjugated polymer in the presence of surface plasmons on metallic nanoparticles is studied. A layered device structure was constructed that enabled control over nanoparticle diameter and separation between the polymer and nanoparticles layers. The dependence of the surface plasmon evanescent field and energy transfer has been investigated with the largest enhancement in photoluminescence observed at a 40 nm distance separation between the fluorophore and the surface plasmon. A spectrum of surface plasmon resonances ranging from the emission to the absorption energies of the conjugated polymer revealed largest enhancements when the resonance was tuned to the conjugated polymer emission energy. At peak photoluminescence the maximum photoluminescent enhancement was found to be 5.6 times of the photoluminescence of the control structure and the total integrated enhancement was 5.9 times.     

Stable blue-green and ul traviolet photoluminescence from silicon carbide on porous silicon

β-Silicon carbide layers have been prepared by high temperature pyrolysis of polyimide Langmuir-Blodgett films on porous silicon substrate in vacuum. The formation of silicon carbide is confirmed by the IR and XRD spectra. It is found that photoluminescence still exists and appears in the blue-green and ultraviolet regions after thermal treatment at 900°C. These results indicate that the silicon carbide layers, which are formed, are responsible for the blue-green luminescence.