用于制备SOI材料的基于硅片键合和双层多孔硅剥离的薄外延硅膜转移技术

采用在阳极化反应时改变电流强度的办法 ,在高掺杂的 P型硅 (111)衬底上制备了具有不同多孔度的双层结构多孔硅层 .用超高真空电子束蒸发技术在多孔硅表面外延生长了一层高质量的单晶硅膜 .在室温下 ,该外延硅片同另一生长有热二氧化硅的硅片键合在一起 ,在随后的热处理过程中 ,键合对可在多孔硅处裂开 ,从而使外延的单晶硅膜转移到具有二氧化硅的衬底上以形成 SOI结构 .扫描电镜、剖面投射电镜、扩展电阻和霍尔测试表明 SOI样品具有较好的结构和电学性能     

用于制备SOI材料的基于硅片键合和双层多孔硅剥离的薄外延硅膜转移技术

采用在阳极化反应时改变电流强度的办法,在高掺杂的P型硅(111)衬底上制备了具有不同多孔度的双层结构多孔硅层.用超高真空电子束蒸发技术在多孔硅表面外延生长了一层高质量的单晶硅膜.在室温下,该外延硅片同另一生长有热二氧化硅的硅片键合在一起,在随后的热处理过程中,键合对可在多孔硅处裂开,从而使外延的单晶硅膜转移到具有二氧化硅的衬底上以形成SOI结构.扫描电镜、剖面投射电镜、扩展电阻和霍尔测试表明SOI样品具有较好的结构和电学性能.     

基于多孔硅牺牲层技术的压阻式加速度传感器的分析和设计

分析并设计了一种利用高选择自停止的多孔硅牺牲层技术制作压阻式加速度传感器的工艺,并利用外延单晶硅作为传感器的结构材料,这种工艺能精确地控制微结构的尺寸.利用多孔硅作牺牲层工艺,使用加入硅粉和(NH4 ) 2 S2 O8的TMAH溶液通过在薄膜上制作的小孔释放多孔硅,能很好地保护未被覆盖的铝线.该工艺和标准的CMOS工艺完全兼容.     

基于多孔硅牺牲层技术的压阻式加速度传感器的分析和设计

分析并设计了一种利用高选择自停止的多孔硅牺牲层技术制作压阻式加速度传感器的工艺,并利用外延单晶硅作为传感器的结构材料,这种工艺能精确地控制微结构的尺寸.利用多孔硅作牺牲层工艺,使用加入硅粉和(NH4)2S2O8的TMAH溶液通过在薄膜上制作的小孔释放多孔硅,能很好地保护未被覆盖的铝线.该工艺和标准的CMOS工艺完全兼容.     

Mechanism of the subband excitation of photoluminescence from erbium ions in silicon under high-intensity optical pumping

The photoluminescence (PL) excitation spectra of erbium and band-to-band silicon in Si:Er/Si epitaxial structures under high-intensity pulsed optical excitation are studied. It is shown that the nonmonotonic dependence of the PL intensity on the excitation wavelength ??_ex near the absorption edge of silicon is due to inhomogeneity in the optical excitation of the Si:Er active layer. The sharp rise in the erbium PL intensity in the spectral range ??_ex = 980?1030 nm is due to an increase in the excited part of the Si:Er emitting layer on passing to subband light pumping (??_ex > 980 nm) with a low absorption coefficient in silicon because of the effective propagation of the excitation light in the bulk of the structures under study. It is shown that, under the subband optical pumping of Si:Er/Si structures, as also in the case of interband pumping, the exciton mechanism of erbium ion excitation is operative. Excitons are generated under the specified conditions as a result of a two-stage absorption process involving impurity states in the band gap of silicon.     

Formation and characterization of porous silicon films obtained by catalyzed vapor-chemical etching

Porous silicon films obtained by the metal-assisted vapor-chemical etching technique have been characterized. For the film formation, epitaxial (100) N/P⁺, 1–5 Ω cm monocrystalline silicon wafers were used. The vapors of an alcoholic solution of H₂O₂/HF were drawn towards the silicon surface, which was previously covered with a thin layer of gold (~8 nm) for the catalytic etching. For the optical and morphological characterization of porous films, Raman spectroscopy, Ellipsometry, FTIR spectroscopy and SEM images were used. The films thickness kept a linear relationship with etching time. A porosity gradient from the surface towards the interface (65% to 12%) was observed in the films. A large amount of Si–H bonds as related to O–Si–O bonds were observed and the pore size depends on the HF concentration. Irregular morphology was found in films formed with 50% HF.     

Reorganized Porous Silicon Bragg Reflectors for Thin-Film Silicon Solar Cells

Stacks of porous silicon layers have been successfully applied to maximize internal reflection at the interface between a silicon substrate and an epitaxially grown layer. The stack is consist of alternating porous layers of high and low porosity, defined by the quarter-wavelength rule. During the hydrogen bake prior to epitaxial growth of the epitaxial layer, the porous silicon stack crystallizes in the form of thin quasi-monocrystalline silicon layers incorporating large voids. Experimental data of the measured external reflectance have been linked to the internal reflectance. An optical-path-length enhancement factor of seven was calculated in the wavelength range of 900–1200 nm. Application on thin-film epitaxial solar cells showed a 12% increase in short-circuit current and efficiency.     

多孔硅/聚合物复合膜等效折射率的研究

用多孔Si（PS）圆柱空腔二维结构模型,理论研究了TE模式情况下PS／聚合物复合膜的等效折射率,给出了PS等效折射率与孔隙率和嵌入率的关系。实验采用波导耦合m线法分别研究了TE模和TM模入射情况下（633nm波长处）,孔隙率为73%的PS膜嵌入聚合物聚合基丙烯酸甲酯（PMMA）材料后的等效折射率与聚合物嵌入率的关系。理论分析与实验结果基本符合。     

Enhanced optical and electrical stability of thermally carbonized porous silicon

In the current paper, the intrinsic instability of physical properties of porous silicon (PS) was minimized using a thermal carbonization (TC) method. A typical PS showed an obvious quenching of its photoluminescence (PL) properties under long-term laser radiation. To resolve this problem, an ultra-thin stabilizing layer was grown on the porous structure under an acetylene gas flow. During the TC process at high temperatures, carbon atoms were detached from the acetylene molecules and dissolved in the porous structure. Thermally carbonized PS (TC-PS) layer changed the PL peak position of PS slightly due to the formation of Si–C species on porous surface after acetylene exposure. The effects of TC-PS layer in electrical properties of fabricated photodetectors were studied. The photocurrent of freshly prepared PS decreased under prolonged green laser radiation (532 nm, 5 mW), but the TC-PS sample showed more stable electrical characteristics under the same conditions.     

GaN growth on porous silicon by MOVPE

GaN films have been grown at 1050 °C on porous silicon (PS) substrates by metalorganic vapour phase epitaxy. The annealing phase of PS has been studied in temperature range from 300 to 1000 °C during 10 min under a mixture of ammonia (NH₃) and hydrogen (H₂). The PS samples were characterized after annealing by scanning electronic microscope (SEM). We observed that the annealing under the GaN growth conditions does not affect the porous structure.For the growth of the active GaN layer we used a thin AlN layer in order to improve wetting between GaN and PS/Si substrate. The growth of AlN and GaN films was controlled by laser-reflectometry. We estimated the porosity of PS samples from the evolution of the reflectivity signal during the AlN growth. The crystalline quality and surface morphology of GaN films were determined by X-ray diffraction and SEM, respectively. Preferential growth of hexagonal GaN with (0002) direction is observed and is clearly improved when the thickness of AlN layer increases. Epitaxial GaN layers were characterized by photoluminescence.     

Effects of surface passivation in porous silicon as H2 gas sensor

This paper investigates the effects of surface passivation in porous silicon (PS) as a hydrogen gas sensor. Two types of sample have been prepared, one with typical HF anodizing solution and the other with the presence of peroxide (H₂O₂) in the solution. The Fourier transform infrared (FT-IR) measurements on the PS layer on the Si substrate showed that the typical PS surface is characterized by chemical species like Si–H and Si–O. Samples anodized with peroxide based (H₂O₂) solution showed a PS structure with higher porosity (～80%) and better surface passivation (higher concentration of Si–O and Si–H species) compared to those not treated with peroxide. Peroxide based PS sample fabricated as an H₂ gas sensor showed better electrical (I–V) sensitivity compared to those without peroxide, which has been associated with good surface passivation. Surface passivation in peroxide based PS is also maintained at higher temperatures (100 °C).     

Temperature Effects on Photoluminescence Properties of Porous Silicon

The temperature effects on the photoluminescence（PL） properties of porous silicon（PS） have been observed in the early stage. However, the obtained results are different. Through repeated experiments, some different and useful information are got, which benefits us in that PL properties of porous silicon can be fully made use of. Firstly, samples with porosity of 76% and 49% were chosen to study the exciting temperature effects on the PL spectrum. For the samples with low porosity, the decreasing temperature causes the peak wavelength to be red-shifting and that of the samples with high porosity to present the blue-shifting trend. The light intensity of both reaches the maximum at - 10℃. These experimental results can be well explained with the synthesized center PL model based on the quantum confinement model, other than the PL efficiency function σ（λ）. Thereafter, PL properties of PS samples fabricated separately under the temperature of -10 ℃, 0 ℃ , 10 ℃, 20 ℃ and 30 ℃ were studied. The results indicate that with the decrease of the etching temperature, the PL intensity increases from 406.7 to 716.6 and the peak wavelength blue-shifts from 698.9 nm to 671.8 nm. The WHFM of the PL spectrum dramatically narrows. At the same time, the images observed by AFM show that with the decreasing temperature, the holes are becoming deeper and the porosity is higher, which suggests that the decreasing temperature accelerates the etching rate.     

Isolation of silicon film grown on porous silicon layer

We have investigated a new technology for dielectric isolation of a Si film grown epitaxially on a porous silicon layer. After oxidation of the porous silicon layer, a Si on Ohcidized Porous Silicon(SOPS) structure can be obtained. It is proposed that micropores pinch off quickly in the interfacial region between the porous silicon layer and the epitaxial film. A minimum yield calculated from Rutherford backscattering spectra of the epitaxial silicon film is 5.3%, and an electron Hall mobility of 600cm²/V.s is obtained in the film with a carrier concentration of 1 x 10¹⁷ /cm³. MOSFETs were fabricated on the SOPS structure.     

多孔硅的微结构和喇曼光谱

多孔硅（ＰｏｒｏｕｓＳｉｌｉｃｏｎ）是晶体硅于氢氟酸溶液中在硅衬底上形成的多孔态的硅材料。ＰＳ可见光区的强烈光辐射使其成为世界范围的研究焦点。本文用电化学方法制得了ＰＳ结构，扫描电子显微镜（ＳＥＭ）的结果表明ＰＳ是一个硅的毫微结构量子线的网络，光致发光（ＰＬ）谱表明ＰＳ发可见红光，而喇曼光谱显示一个在５１６ｃｍ（－１）附近的非对称峰，说明ＰＳ是一种新型的硅材料。     

Effect of substrate porosity on photoluminescence properties of ZnS films prepared on porous Si substrates by pulsed laser deposition

ZnS films were deposited on porous Si(PS) substrates with different porosities by pulsed laser deposition. The photolumi-nescence spectra of the samples were measured to study the effect of substrate porosity on luminescence properties of ZnS/porous Si composites. After deposition of ZnS films,the red photoluminescence peak of porous Si shows a slight blueshift compared with as-prepared porous Si samples. With an increase of the porosity,a green emission at about 550 nm was observed which may be ascribed to the defect-center luminescence of ZnS films,and the photoluminescence of ZnS/porous Si composites is very close to white light. Good crystal structures of the samples were observed by x-ray diffraction,showing that ZnS films were grown in preferred orientation. Due to the roughness of porous Si surface,some cracks appear in ZnS films,which could be seen from scanning electron microscope images.     

White light photoluminescence from ZnS films on porous Si substrates

ZnS films were deposited on porous Si (PS) substrates using a pulsed laser deposition (PLD) technique.White light emission is observed in photoluminescence (PL) spectra, and the white light is the combination of blue and green emission from ZnS and red emission from PS. The white PL spectra are broad, intense in a visible band ranging from 450 to 700 nm. The effects of the excitation wavelength, growth temperature of ZnS films, PS porosity and annealing temperature on the PL spectra of ZnS/PS were also investigated.     

多孔硅衬底上ZnS薄膜的白光光致发光

通过脉冲激光沉积（PLD）技术在多孔硅（PS）衬底上制备了ZnS薄膜。用光致发光（PL）的方法观察到白光发射,这个白光是由ZnS薄膜的蓝、绿光和PS的红光叠加形成的。白光光致发光谱是一个从450nm 到700nm的较强的可见光宽谱带。同时研究了激发波长、ZnS薄膜的生长温度、PS的孔隙率和退火温度对ZnS/PS光致发光谱的影响。     

多孔硅/聚合物复合膜光学各向异性的研究

首次用二维圆柱孔模型研究了多孔硅/聚合物复合膜的光学各向异性,求出了光学各向异性参数。实验上制备出了多孔硅/PMMA复合膜平面波导,采用棱镜耦合m线方法测量了复合膜的折射率。理论分析与实验结果基本相符。研究结果表明,多孔硅膜呈现出正单轴晶体的特征,由TE和TM模射所确定的折射率分别对应寻常光折射率和非寻常光折射率。多孔硅/PMMA复合膜光学各向异性随聚合物嵌入率的增加而减小。光学各向异性也随孔隙率的不同而变化,当初始孔隙率为73%时,光学各向异性参数β取最大值。     

多孔硅外延转移技术制备以氮化硅为绝缘埋层的SOI新结构

为减少自加热效应 ,利用多孔硅外延转移技术成功地制备出一种以氮化硅为埋层的 SOI新结构 .高分辨率透射电镜和扩展电阻测试结果表明得到的 SOI新结构具有很好的结构和电学性能 ,退火后的氮化硅埋层为非晶结构 .     

Specific features of formation of GaAs nanowire crystals during molecular beam epitaxy on different silicon surfaces

The results of experimental studies on the growth and the morphological and structural properties of GaAs nanowire crystals on different silicon surfaces are reported. It is shown that the nonplanar geometrical layout of growth allows the production of epitaxial nanowire crystals in a system with a large lattice mismatch. The growth on porous substrates, the role of the surface orientation, high-temperature annealing, and presence of an oxide layer at the surface, and some other effects typical of growth of III–V nanowire crystals on the Si surface are studied and analyzed. Intense emission from the array of GaAs nanowire crystals grown on the Si (111) surface is observed.