Influence of SnO2 coating and annealing on the luminescence properties of porous silicon nanowires

Porous silicon (PS)-core/SnO₂-shell nanowires (NWs) were synthesized by a two step process: electrochemical anodization of silicon followed by atomic layer deposition of SnO₂. The photoluminescence spectrum of the PS nanowires showed a broad blue green emission band centered at approximately 510 nm. PL measurement also showed that the blue green emission was enhanced by SnO₂ coating and enhanced further by thermal annealing. It appeared that annealing in a reducing atmosphere was more efficient in increasing the blue green emission intensity than annealing in an oxidizing atmosphere. Energy-dispersive X-ray spectroscopy revealed that the enhancement in the blue green emission by annealing in a reducing atmosphere was attributed to the formation of Sn interstitials in the PS cores due to the dissociation of the SnO₂ shells followed by the diffusion of the Sn atoms, generated as a result of the dissociation of SnO₂, into the PS cores during the annealing process.     

Effect of annealing in various atmospheres on the photoluminescence of porous silicon

The effect of isochronous annealing in various atmospheres on the photoluminescence of porous p-type silicon samples obtained by anodization under identical conditions was studied. Comparative experimental data for the samples annealed in air, nitrogen, and vacuum are presented.     

多孔硅在高温退火过程中结构变化的研究

采用电化学腐蚀的方法制备了不同孔径的多孔硅薄膜样品,并在1050℃高温下进行了退火。采用扫描电镜和拉曼光谱对多孔硅退火前后结构的变化进行了观察,根据晶体形核理论分析了孔径变化的机理,并从热力学角度对其微观机制进行了讨论。实验和理论分析的结果均表明,多孔硅的初始孔径存在一个临界值,初始孔径小于此临界值时,孔在高温退火中有收缩的趋势;反之,初始孔径大于此临界值时,孔有变大的趋势。     

Influence of microwave annealing on direct bonded silicon wafers

Strong and nearly void free bonding was achieved using direct bonding followed by microwave annealing. Silicon wafers were cleaned, O₂ plasma surface activated, and bonded at room temperature. After microwave annealing at 400 °C, the bond strength of hydrophilic wafers was found to be in the range between 0.2 and 1.6 J/m². Additional heating of bonded wafers was done at elevated temperatures and for prolonged times using either rapid thermal annealing or microwave annealing. In either case, additional annealing showed no impact on wafer separation area, void, or bond strength. Thus, the initial microwave anneal dictated the ultimate bond strength regardless of subsequent annealing method. The mechanism for wafers bonded in this work involved dipole-dipole bonding and, hydrogen bonding. The initial microwave anneals typically required times less than 60 min. As a result, microwave annealing was shown to be a promising low temperature alternative for wafer bonding when compared to the currently used mechanical furnace anneals.     

Thermal conductivity and nanoindentation hardness of as-prepared and oxidized porous silicon layers

Porous silicon (PS) offers promising possibilities to be applied as thermal insulating material in thermal effect microsystems for its thermal conductivity (TC) is up to two orders smaller than that of bulk silicon. In order to find a compromise between efficient thermal isolation and good mechanical stability of PS, thermal oxidation of PS is commonly used to tune the mechanical and thermal properties of PS. Both TC and the hardness of as-prepared and oxidized PS have been thoroughly investigated. TC and the hardness of as-prepared and oxidized PS were measured using micro-Raman scattering and nanoindentation, respectively. Experimental results revealed that TC and the hardness of as-prepared PS, exhibiting a strong dependence on the preparing conditions, decrease with increasing porosities. After oxidization at different temperatures, TC of oxidized PS decreases with increasing oxidation temperatures, whereas the hardness increases a lot. PS with a moderate porosity of 73.4% oxidized at 600 °C has a compromise between low TC [2.100 W/(m K)] and high hardness (∼1.160 GPa). So this process finalizes this kind of oxidized PS to be used as a suitable thermal insulation substrate in thermal effect microsystems.     

Thermal annealing of porous silicon to develop a quasi monocrystalline structure

Low porosity (~20–30%) porous silicon produced by electrochemical anodization was annealed in the temperature range 1000–1150 °C under pure hydrogen atmosphere and under hydrogen mixed with nitrogen in different proportions for a duration of 15–60 min. Porous silicon was transformed to quasi monocrystalline porous silicon (QMPS) in the temperature range 1050–1100 °C under pure hydrogen atmosphere. The crystallinity was confirmed by grazing incidence X-ray diffraction. Field emission scanning electron microscopic (FESEM) studies revealed that the surface layer is pore free with a few voids embedded inside the body. Atomic force microscopic (AFM) studies confirmed relatively smooth and uniform surfaces under the same annealing conditions. Our experimental results concluded that the recrystallization of porous silicon at 1100 °C and in presence of pure hydrogen exhibits lower reflection loss compared to bulk crystalline silicon. Also the electrical resistivity of QMPS makes it suitable for optoelectronic devices and solar cells.     

制备温度对多孔硅光学特性的影响(英文)

本文不同的温度下制备多孔硅.通过荧光光谱、光吸收谱、X射线光电子谱研究了多孔硅的光和结构特性.研究结果表明存在着一个制备临界温度343 K,当制备温度从临界温度之下提高到临界温度之上时,多孔硅的荧光和光吸收从红移转向蓝移,同时硅2p电子结合能也从减小转向增大.     

电化学阳极氧化条件对阵列多孔硅的影响

采用电化学阳极氧化法,将预光刻图案的p型硅片制备成阵列多孔硅.讨论电化学阳极氧化条件对阵列多孔硅形貌的影响.结果表明:随着HF浓度、电流密度、阳极氧化时间的增大,阵列多孔硅的孔深逐渐加大;当HF:C2H5OH:H2O(体积比)为1:1:1～1:2:5,电流密度为1.56mA/cm2,阳极氧化时间为3h时,制备出的阵列多孔硅具有比较规整的阵列孔,并且孔深能够达到50pm;表面活性剂对阵列孔的形成有很大影响,加入表面活性剂后形成的孔才具有一定的规整性以及深宽比.     

Influence of surface wettability on the cathodic electroluminescence of porous silicon

It is shown that the wettability of porous silicon influences the efficiency of its cathodic electroluminescence in electrolytes. A model is proposed to explain the nature of the electroluminescence in a system consisting of porous silicon and an oxidizing electrolyte. Pis’ma Zh. Tekh. Fiz. 23, 58–63 (January 12, 1997)     

Influence of pressure annealing on electrical properties of Mn implanted silicon

The effect of annealing at 610-720 K under enhanced hydrostatic pressure (HP) on electrical properties of manganese implanted Czochralski grown silicon (CzSi:Mn) and floating zone grown silicon (FzSi:Mn) (doses up to 1×10¹⁶ cm⁻¹, E=160 keV) was investigated by electrical C-V, I-V and admittance measurements. Mn⁺ implantation produces both donor-like and acceptor-like implantation-induced defects. The stress-induced decrease in the hole concentration was detected in CzSi implanted by Mn⁺ and annealed at temperatures 610-670 K. The effect of changing initial conductivity of CzSi:Mn samples of high concentration of interstitial oxygen, from p type to n type, due to thermal donors (TDs) generation has been observed. The electron concentration after type conversion depends on annealing conditions and Mn⁺ dose. The TDs generation has not been detected in FzSi:Mn samples containing lower oxygen concentration, however, the FzSi:Mn samples annealed at 720 K under 10⁵ Pa for 10 h indicate at the implanted side the increased carrier concentration due to the defects produced by Mn⁺ implantation. The heat treatment of FzSi:Mn under HP at 720 K for 10 h results in further increase of carrier concentration due to the defect generation.     

Specific contact resistance and metallurgical process of the silver-based paste for making ohmic contact structure on the porous silicon/p-Si surface of the silicon solar cell

Porous silicon has been considered as a promising optoelectronic material for developing a variety of optoelectronic devices and sensors. In the present study, the electrical properties and metallurgical process of the screen-printed Ag metallization formed on the porous silicon surface of the silicon solar cell have been investigated. The contact structure consists of thick-film Ag metal contact patterned on the top of the porous silicon surface. The sintering process consists of a rapid firing step at 750–825 °C in air ambient. It results in the formation of a nearly perfect contact structure between the Ag metal and porous silicon/p-Si structure that forms the top metalization for the screen-printed silicon solar cells. The SEM picture shows that Ag metal firmly coalesces with the silicon surface with a relatively smooth interfacial morphology. This implies that high temperature fire-through step has not introduced any signs of adverse effect of junction puncture or excessive Ag indiffusion, etc. The three-point probe (TPP) method was applied to estimate the specific contact resistance, ρ _c (Ω-cm²) of the contact structure. The TPP measurement shows that contact structure has excellent ohmic properties with ρ _c = 1.2 × 10⁻⁶ Ω-cm² when the metal contact sintered at 825 °C. This value of the specific contact resistance is almost three orders of magnitude lower than the corresponding value of the ρ _c = 7.35 × 10⁻³ Ω-cm² obtained for the contact structure sintered at 750 °C. This improvement in the specific contact resistance indicates that with increase in the sintering temperature, the barrier properties of the contact structure at the interface of the Ag metal and porous silicon structure improved which in turn results a lower specific contact resistance of the contact structure.     

Features of the current-voltage characteristics and temperature dependences of electric conductivity in porous silicon layers

A method of separating porous silicon (por-Si) layer without deformation from a silicon substrate, which virtually excludes almost any risk of subsequent degradation of the isolated por-Si layer is proposed. The current-voltage characteristics of por-Si have been measured in a temperature interval of 300–255 K. Direct measurements of the conductivity of por-Si have been performed for the first time and it is established that the conductivity has an activation nature for the current passage parallel to the por-Si sample surface.     

大气中烧结多孔氮化硅的相变和氧化机理研究

以α—Si3N4为原料，分别以Y2O3-Al2O3和MgO-Al2O3-SiO2两个体系作为烧结助剂，在大气中对氮化硅坯体在1400～1550℃进行烧结。研究了烧结温度、烧结助剂体系对氮化硅的氧化程度、氧化产物的影响。结果表明，以MgO-Al2O3-SiO2作烧结助剂有利于α-Si3N4转变为β-Si3N4，且该烧结助剂体系的的抗氧化能力也明显优于Y2O3-Al2O3体系。氮化硅在不同温度烧结时形成的氧化产物不同。     

Stabilization of luminous properties of porous silicon by vacuum annealing at high temperatures

The degradation properties of porous silicon caused by vacuum annealing at high-temperatures have been measured. Vacuum annealing within the temperature range of 150–300°C provided the complete removal of water molecules from the pore surface and partial destruction of hydrogen complexes. Our studies showed that vacuum annealing at 150°C considerably stabilizes the luminous properties of porous silicon: the subsequent UV-irradiation of silicon specimens changed the photoluminescence intensity only by 8–10% of its initial value.     

The modification of the properties of n-type conductivity porous silicon by argon ion irradiation

The results of the research into the influence of argon ion irradiation at 3 keV on the composition and structure of porous silicon are presented. At a certain angle of incidence of the particles relative to the surface of the monocrystallites, an undulating λ∼60 nm nanorelief is formed, while the crystallite sizes and structure remain unchanged. The IR-spectroscopy data show that SiH groups are mainly localized in a thin 120 nm near-surface layer. During exposure of the samples to the air in the dark, monohydride groups are removed from the surface within a month. Dihydride groups, located in deeper layers, are oxidized considerably more slowly than the monohydride ones. The experimental data show that the 0.1 μm-thick surface layer serves as a diffusion barrier preventing oxygen from penetrating deep into the porous silicon.     

Influence of primary annealing on Goss development in grain oriented silicon steels

Abstract

Two different primary annealing conditions (continuous heating and discontinuous heating) on conventional oriented silicon steel were employed, and the evolution of microstructure and Goss frequency, as well as orientations of Goss neighbourhood from recovery to secondary recrystallisation, was investigated by means of optical microscopy and advanced electron backscatter diffraction (EBSD) technique. It could be concluded that high Goss frequency before secondary recrystallisation possibly did not contribute to sharp Goss orientation, even excellent magnetic property and that no grains with less deviation from ideal Goss first began to grow. As for coincidence site lattice (CSL) grain boundary and high energy grain boundary theories, the latter can explain the development of Goss due to its high frequency compared with CSL boundary of low frequency.     

热敏材料掺磷非晶硅的退火行为

本文对PECVD制备的红外热敏材料掺磷非晶硅薄膜的两个关键热电参数-红外吸收系数和电阻温度系数-采用红外透射谱、拉曼谱和电阻率测量进行了深入的研究。实验结果表明,对样品进行退火30min后,薄膜结构可以达到稳定;随着退火温度的增加,样品的红外透射率下降;当退火温度达到700℃时,薄膜完全晶化;与此同时,电阻率和电阻温度系数随掺杂浓度和退火温度的增加而减小。根据Lu的模型,对这些现象进行了解释并给出了制备和退火的优化条件。     

Extending electrical resistivity measurements in micro-scratching of silicon to determine thermal conductivity of the metallic phase Si-II

The aim of this work to analyse the relationships between parameters of concrete surface geometry determined with various methods as well as their relations to adhesion in repair systems. Several types of concrete preparation techniques were selected to obtain different levels of surface roughness of concrete substrates. Four measurement techniques, corresponding to different levels of observation, have been used to characterize the surface geometry: laser profilometry, mechanical profilometry, a microscopic method and a “sand” (macroscopic) method. The correlations between parameters describing surface geometry are determined. The relationships between bond strength and selected parameters of surface geometry are also discussed.     

Influence of annealing on the phase composition,transmission and resistivity of SnOx thin films

Undoped and antimony-doped tin oxide films were prepared by d.c. reactive ion sputtering in an argon atmosphere with oxygen partial pressures ranging from 0 to 50%. The films were annealed in air, nitrogen and a vacuum in the temperature range 570–750 K. The influence of thermal annealing on the structural properties, electrical resistance and optical transmittance is described.