Deposition and structural characteristics of cadmium sulfide (CdS) thin films by chemical bath deposition (CBD) technique from a bath containing thiourea,cadmium acetate,ammonium acetate and ammonia in an aqueous solution are reported.Researches are made on the influence of the fundamental parameters including pH,temperature,and concentrations of the solution involved in the chemical bath deposition of CdS and titration or dumping of the thiourea solution on the structure characteristic of CdS thin films.The pH of the solution plays a vital role on the characteristic of the CdS thin films.The XRD patterns show that the change in the pH of the solution results in the change in crystal phase from predominant hexagonal phase to predominant cubic phase.The CdS thin films with the two different crystal phases have different influences on CIGS thin film solar cells.The crystal mismatch and the interface state density of the cCdS(cubic phase CdS) and CIGS are about 1.419% and 8.507×1e12cm-2 respectively,and those of the h-CdS(hexagonal phase CdS) and CIGS are about 32.297% and 2.792×1e12cm-2 respectively.It is necessary for high efficiency CIGS thin film solar cells to deposit the cubic phase CdS thin films.
A Si p-π-n diode with β-FeSi2 particles embedded in the unintentionally doped Si (p-type) was designed for determining the band offset at β-FeSi2-Si heterojunction. When the diode is under forward bias,the electrons injected via the Si np- junction diffuse to and are confined in the β-FeSi2 particles due to the band offset. The storage charge at theβ-FeSi2-Si heterojunction inversely hamper the further diffusion of electrons,giving rise to the localization of electrons in the p-Si near the Si junction, which prevents them from nonradiative recombination channels. This results in electroluminescence (EL) intensity from both Si and β-FeSi2 quenching slowly up to room temperature. The temperature dependent ratio of EL intensity of β-FeSi2 to Si indicates the loss of electron confinement following thermal excitation model. The conduction band offset between Si and β-FeSi2 is determined to be about 0.2eV.
H-gate and closed-gate PD SOI nMOSFETs are fabricated on SIMOX substrate,and the influence of floating body effect on the radiation hardness is studied.All the subthreshold characteristics of the devices do not change much after radiation of the total dose of 1e6rad(Si).The back gate threshold voltage shift of closed-gate is about 33% less than that of Hgate device.The reason should be that the body potential of the closed-gate device is raised due to impact ionization,and an electric field is produced across the BOX.The floating body effect can improve the radiation hardness of the back gate transistor.
Design and fabrication of Schottky barrier diodes (SBD) with a commercial standard 0.35μm CMOS process are described.In order to reduce the series resistor of Schottky contact,interdigitating the fingers of schottky diode layout is adopted.The I-V,C-V,and S parameter are measured.The parameters of realized SBD such as the saturation current,breakdown voltage,and the Schottky barrier height are given.The SPICE simulation model of the realized SBDs is given.
A unified breakdown model of SOI RESURF device with uniform,step,or linear drift region doping profile is firstly proposed.By the model,the electric field distribution and breakdown voltage are researched in detail for the step numbers from 0 to infinity.The critic electric field as the function of the geometry parameters and doping profile is derived.For the thick film device,linear doping profile can be replaced by a single or two steps doping profile in the drift region due to a considerable uniformly lateral electric field,almost ideal breakdown voltage,and simplified design and fabrication.The availability of the proposed model is verified by the good accordance among the analytical results,numerical simulations,and reported experiments.
A novel high reflectivity type of semiconductor saturable absorption mirror grown by metal organic chemical vapor deposition is presented. Using the mirror as well as an end mirror,passively mode locked Yb∶YAB laser is realized,which produces a pulse as short as 305ps at 1.044μm.The pulse frequency is 375MHz;the output power is 45mW.
A novel design of 100GHz-spaced 16channel arrayed-waveguide grating (AWG) based on silica-on-silicon chip is reported.AWG is achieved by adding a Y-branch to the AWG and arranging the input/output channel in a neat row, so the whole configuration can be aligned and packaged using only one fiber-array. This configuration can decrease the device’s size, enlarge the minimum radius of curvature, save time on polishing and alignment, and reduce the chip’s fabrication cost.
A cylindrical gates model of the static induction transistor is proposed and mirror method is used to calculate the distribution of electric potential.The results show that:the potential barrier is directly determined by channel over pinchedoff factor;gate efficiency η decreases as the gate dimension α2 and shifted gate voltage are minished,and what differs from the firstorder theory is that η will tend to zero at the shifted gate voltage tends to zero when VD=0;at low current,the voltage amplification factor μ increases as the drain current rising.When the drain current reaches certain degree,the voltage amplification factor keeps almost constant.In the end,an analytical description of SIT’s characteristic suited to both triodelike and mixed I-V characteristics are obtained.The predicted I-V curves are consistent perfectly with the reported experimental ones.
Nitrogen implantation in silicon substrate at fixed energy of 35keV and split dose of 1e14~5×1e14cm-2 is performed before gate oxidation.The experiment results indicate that with the increasing of implantation dose of nitrogen,oxidation rate of gate decreases.The retardation in oxide growth is weakened due to thermal annealing after nitrogen implantation.After nitrogen is implanted at the dose of 2×1e14cm-2,initial O2 injection method which is composed of an O2 injection/N2 annealing/main oxidation,is applied for preparation of 3.4nm gate oxide.Compared with the control process,which is composed of N2 annealing/main oxidation,initial O2 injection process suppresses leakage current of the gate oxide.But Qbd and HF C-V characteristics are almost identical for the samples fabricated by two different oxidation processes.
A novel bonding method using silicate gel as bonding medium is developed.High reflective SiO2/Si mirrors deposited on silicon substrates by e-beam deposition are bonded to the active layers at a low temperature of 350℃ without any special treatment on bonding surfaces.The reflectivities of the mirrors can be as high as 99.9%.A Si.based narrow band response InGaAs photodetector is successfully fabricated,with a quantum efficiency of 22.6% at the peak wavelength of 1.54μm,and a full width at half maximum of about 27nm.This method has a great potential for industry processes.
A 1×8 multimode interference power splitter with multimode input/output waveguides in SOI material is designed by the beam propagation method and fabricated by the inductive coupled plasma etching technology for use in fiber optics communication systems.The fabricated device exhibits low loss and good coupling uniformity.The excess loss is lower than 0.8dB,and the uniformity is 0.45dB at the wavelength of 1550nm.Moreover,the polarization dependent loss is lower than 0.7dB at 1550nm.The device size is only 2mm×10mm.
Resonant accelerometer is designed,which includes two doubleended tuning forks,a proof mass,fourleverage system amplifying inertial force,and drive/sense combs.Each tuning fork is electrostatically actuated and sensed at resonance using comb electrodes.The device is fabricated using MEMS bulk-silicon technology,whose sensitive degree is 27.3Hz/g,and the resolution is 167.8μg.
To minimize the power consumption with resources operating at multiple voltages a timeconstrained algorithm is presented.The input to the scheme is an unscheduled data flow graph (DFG),and timing or resource constraints.Partitioning is considered with scheduling in the proposed algorithm as multiple voltage design can lead to an increase in interconnection complexity at layout level.That is,in the proposed algorithm power consumption is first reduced by the scheduling step,and then the partitioning step takes over to decrease the interconnection complexity.The timeconstrained algorithm has time complexity of O(n2),where n is the number of nodes in the DFG.Experiments with a number of DSP benchmarks show that the proposed algorithm achieves the power reduction under timing constraints by an average of 46.5%.
假设超晶格“折沟道”对粒子的作用等效为形状相似的周期调制,利用正弦平方势把粒子运动方程化为具有阻尼力和周期调制的非线性微分方程.利用Melnikov方法分析了系统的全局分叉和它的混沌行为.指出了超晶格沟道效应的无规现象与系统混沌的相关性.
利用蒙特卡罗方法对SiGe/Ge/SiGe异质结构的自旋极化输运特性进行了模拟研究.在Ge沟道调制掺杂异质结构形成的二维空穴气中,空穴的自旋进动主要受Rashba自旋轨道相互作用控制.在77~300K的温度范围内,对自旋散射长度、自旋极化率等自旋极化输运特性进行了研究.模拟结果显示,低温和窄宽度沟道有利于减小散射对自旋极化输运的影响,避免自旋极化率衰减,增大自旋散射长度.栅控的漏端电流自旋相关效应使器件跨导增大,并产生负跨导效应.
研究了非故意掺杂和掺Si的n型GaN外延材料持续光电导的光淬灭。实验发现非故意掺杂GaN的持续光电导淬灭程度远大于掺Si的n型GaN;撤去淬灭光后前者的持续光电导几乎没有变化,后者的却有明显减小;稍后再次加淬灭光前者的持续光电导无变化,而后者的有明显增加。我们认为两者持续光电导的形成都与空穴陷阱有关,用空穴陷阱模型解释了非故意掺杂GaN持续光电导的形成以及淬灭;认为掺Si的n型GaN的持续光电导是电子陷阱(杂质能级)和空穴陷阱共同作用的结果,并且在持续光电导发生的不同阶段其中一种陷阱的作用占主要地位。
在InP(001)衬底上使用分子束外延技术自组织生长了多周期InAs/InAlGaAs量子点阵列结构。根据对透射电镜和光致发光谱结果的分析,认为引入与InP衬底晶格匹配的InAlGaAs缓冲层可以获得较大的InAs量子点结构,而InAlGaAs层的表面特性对InAs量子点的结构及光学性质有很大影响。对InP基InAlGaAs缓冲层上自组织量子点的形核和演化机制进行了探讨,提出量子点的演化过程表现为量子点的合并长大并伴随着自身的徙动,以获得能量最优的分布状态。
采用射频磁控溅射法在玻璃衬底上制备出高质量的镓掺杂氧化锌(ZnO∶Ga)透明导电膜,并对薄膜的结构和光电特性以及制备参数对薄膜性能的影响进行了研究.制备的ZnO∶Ga是具有六角纤锌矿结构的多晶薄膜,最佳择优取向为(002)方向.薄膜的最低电阻率达到了3.9×10-4Ω·cm,方块电阻约为4.6Ω/□,薄膜具有良好的附着性,在可见光区的平均透过率达到90%以上.
为了生长能满足器件制作所需的外延片,采用低压金属有机物化学气相沉积(LP-MOCVD)方法在半绝缘InP衬底上生长了InP/InGaAs异质结双极晶体管(HBT)结构,1.55μm多量子阱激光二极管(MQW LD)以及两者集成的光发射光电集成电路(OEIC)材料结构。激光器结构的生长温度为655℃,有源区为5个周期的InGaAsP/ InGaAsP多量子阱(阱区λ=1.6μm,垒区λ=1.28μm);HBT结构则采用550℃低温生长,其中基区采用Zn掺杂,掺杂浓度约为2×1019 cm-3。对生长的各种结构分别进行了X射线双晶衍射,光致发光谱(PL)和二次离子质谱仪(SIMS)测试,结果表明所生长的材料结构已满足制作器件的要求。
采用直流磁控溅射法制备TiO2薄膜,在不同温度下对薄膜进行退火,研究了薄膜晶体结构随退火温度的转化情况.对TiO2薄膜氧敏器件特性进行了测试,结果表明,在400℃下灵敏度随氧分压增加最快,并且在400℃具有最高的灵敏度.得到的激活能为0.41eV,并对TiO2薄膜氧敏器件的氧敏可逆性进行了讨论.
以钛酸丁酯为无机原料、二乙醇胺作稳定剂,加入聚乙二醇(PEG)作模板制备前驱体溶胶,通过溶胶-凝胶工艺和浸渍提拉技术在玻璃基片上制备了孔径在10~1000nm范围内可调的纳米TiO2多孔薄膜.通过ESEM,AFM,UV-VIS,N2吸附,XPS和XRD等测试手段研究了PEG(1000)的加入量对薄膜结构及性能的影响.结果表明,当100mL溶胶中PEG的加入量在4.0g左右时,可以得到三维扩展的多孔结构,孔的形状规则且分布均匀,孔径为200~500nm,薄膜比表面积可达76.1m2/g,而过多的PEG加入量反而导致薄膜性能下降.
介绍了一种简单而准确地确定薄膜光学常数和厚度的方法.借助于Forouhi-Bloomer物理模型,用改进的单纯形法拟合分光光度计透过率测试曲线,获得半导体薄膜的光学常数和厚度.对射频磁控溅射和直流反应溅射制备的玻璃基板上的α-Si和ZnO薄膜进行了实验,拟合的理论曲线和实验曲线吻合得非常好.计算得到的结果与文献报道的结果和台阶仪的测量结果一致,误差小于4%.该方法对无定形或多晶的半导体薄膜都适用,也可以用于计算厚度较薄的薄膜.
研究了多晶硅的浓磷扩散吸杂、铝吸杂、磷-铝联合吸杂(双面蒸铝).采用准稳态光电导衰减法测试了吸杂前后多晶硅片的有效少数载流子寿命,发现磷铝联合吸杂于硅片少子寿命的提高最大达30μs以上,其次是磷吸杂,铝吸杂再次之.采用吸杂后的多晶硅片制备了1cm×1cm的太阳电池,与相同条件下未经吸杂制备的电池相比,发现三种吸杂方式都能提高电池的各项电学特性,其中磷铝联合吸杂提高电池效率最大,达40%以上,最差为铝吸杂,只有15%左右的提高,这与吸杂后所测得的少子寿命的变化趋势一致.实验说明三种吸杂方式在不同程度上促成了硅片界面晶格应力对重金属杂质的吸附作用,减少了载流子的复合中心,从而提高了有效少数载流子的寿命;而有效少数载流子的寿命直接影响到电池的效率.
为研究单基极薄基区晶体管的特性,设计了一种单侧基极引出结构薄基区的晶体管,在p型SOI衬底上全离子注入实现了基区宽度为80nm的npn纵向结构,基区的平均浓度为1e18cm-3.经过版图设计和工艺流片,在2μm实验工艺线上研制了这种器件.基极采用电压输入,Vbe在1.1V附近,跨导和电流增益都达到峰值,小信号电流增益βac(ΔIc/ΔIb)=2.7,小信号跨导gmac(ΔIc/ΔVbe)=0.45mS,且gmac/gm(Ic/Vbe)比βac/β(Ic/Ib)大得多,跨导比电流增益更能准确地描述器件特性,这种器件更倾向于电压控制型器件,特别适用于数字电路的开发和应用.
研究了采用向SIMOX圆片埋氧层中注入F离子的方法来改善SIMOX的抗总剂量辐射能力,通过比较未注F样品和注F样品的辐照前后SIMOX器件Ids-Vgs特性和阈值电压,发现F具有抑制辐射感生PMOSFET和NMOSFET阈值电压漂移的能力,并且可以减小NMOSFET中由辐照所产生的漏电流。说明在SOI材料中前后Si/Si02界面处的F可以减少空穴陷阱浓度,有助于提高SIMOX的抗总剂量辐射能力。
设计了双梯度掺杂漂移机制InP/GaP光二极管,研究了由于晶体不匹配所造成的缺陷以及这些缺陷对器件性能的影响.结果表明InP/GaP光二极管具有很好的光谱响应和抗辐射特性,特别是在短波方向有高于80%的内量子效率.这说明在双梯度掺杂漂移机制结构中使用晶格不匹配的衬底时,外延晶体中所产生的缺陷对器件性能的影响较小,器件在有大量缺陷和复合中心存在的情况下仍然可以具有较好的光电特性,从而为在强辐射带轨道运行的航天器使用太阳电池以及InP/Si器件技术提供了很好的设计依据.
基于垂直腔半导体光放大器(VCSOA)双稳模型,从数值上分析了VCSOA的双稳条件、双稳控制以及双稳环简并下的AND逻辑实现.结果表明,在阈值附近(大于阈值的93%)和初始相位失谐量为负的情况下,输出光功率出现双稳态.偏置电流为阈值的98%时,输入光功率在5.5μW和2.2μW处发生上下跳变的结果与实验报道结果吻合得较好.同时,从理论上给出了偏置电流、相位失谐量、线宽展宽因子、顶端面反射率等控制参数对VCSOA开关功率、跳变点、双稳环宽和环宽简并以及对比度的影响规律.
提出利用紫外光聚合反应来制作聚合物光栅的方法.实验发现,光栅的表面起伏深度很小,约为12.4~0.7nm;折射率调制较大,达到0.010左右.这种方法在低阶分布反馈聚合物激光器的制作中具有很好的应用前景.
针对硅热流量传感器的封装,给出了其一维简化理论模型,并采用有限元分析工具ANSYS/FLOTRAN,建立了该封装结构的热模型.模拟结果显示,该封装后的传感器的温度场与未封装传感器相似,证明陶瓷封装结构是可行的;同时比较了封装前后传感器性能的差异,并进一步分析了传感器的热性能和其特征尺寸的关系.该模型的建立,可以减少大量的模拟分析过程,减小计算量,研究结果将为该传感器封装的进一步优化设计提供理论参考和依据.
分析了梳齿电容式传感器梳齿极板间的不平行在三种电容驱动下,对传感器的可靠性工作范围的影响。结果表明梳齿电容在同样的电压驱动下,当电容极板间的倾斜角由0.1度变到0.5度时,单边电容结构和双边电容结构的可靠工作范围分别变为电容极板完全平行时的0.45、0.56。对力平衡的双边梳齿电容结构,当倾斜角由0.1o变到0.15o时,可靠工作范围分别变为原来的0.925。并针对DRIE工艺刻蚀梳齿的原理,讨论了改进方法。
分析了微加工悬臂梁在横向冲击下的响应.将悬臂梁看作一个质量分布参数系统,利用模态叠加法计算悬臂梁在冲击下的位移和应力分布,并根据位移和应力的最大值判断悬臂梁可能的失效模式,从而为MEMS器件的可靠性设计提供依据.
提出了一种新结构发射电路,适用于10/100MHz Base TX以太网,兼容10MHz Base TX和100MHz Base TX两种工作模式,并能在这两种模式间自由切换.电路采用了波形整形,斜率控制,复用线驱动器等技术,使所有参数符合IEEE802.3标准.芯片在SMIC的0.18μm CMOS工艺流片测试,电源电压为3.3V.
在新型的共振隧穿二极管(RTD)器件与PHEMT器件单片集成材料结构上,研究和分析了分立器件的制作工艺,给出了分立器件的制作工艺参数.利用上述工艺成功制作了RTD和PHEMT器件,并在室温下分别测试了RTD器件和PHEMT器件的电学特性.测试表明:在室温下,RTD器件的峰电流密度与谷电流密度之比提高到1.78;PHEMT器件的最大跨导约为120mS/mm,在Vgs=0.5V时的饱和电流约为270mA/mm.这将为RTD集成电路的研制奠定工艺基础.
利用乙二醇本身的分子结构和氢键在10万级的超净环境下成功进行了多层乙二醇环境下的硅/硅直接键合,在氮气保护下1100℃热处理后进行了拉力强度测试,平均键合强度达到了10Mpa,SEM观测表明,在键合界面没有发现孔洞和空隙。这为发展多层结构、多功能集成的MEMS结构器件奠定了良好的工艺基础。
针对超深亚微米芯片设计中的开关盒布线问题提出了可变参数的串扰优化布线算法.该算法充分利用了双层布线资源,将动态信号波形和耦合电容结合起来考虑,进一步减小了线网间的总串扰,并力求通孔数最少.实验证明,本算法能够获得更加优化的布线方案.
对多孔硅施加阳极氧化表面处理技术,可有效解决多孔硅干燥时出现龟裂及坍塌,破坏原有多孔硅的形貌和本质的问题.阳极氧化表面处理技术就是使用少量的负离子作用于多孔硅表面,满足SI分子化合价的需要,消除悬空键,促使多孔硅表面性能稳定,避免结构重组产生分子间的不均匀内应力,从而获得性能稳定、可靠、在空气中可以长期干燥保存的多孔硅.
用基于改进的RCA清洗液结合兆声清洗法和离心喷射法清洗抛光的硅片,干燥后用激光扫描法测试抛光硅片表面颗粒.结果表明,改进的RCA清洗液结合兆声的清洗方法对于去除硅片表面的微小颗粒具有更高的效率.
Studies on first GaN-based blue-violet laser diodes(LDs) in China mainland are reported.High quality GaN materials as well as GaN-based quantum wells laser structures are grown by metal-organic chemical vapor deposition method.The X-ray double-crystal diffraction rocking curve measurements show the fullwidth half maximum of 180″ and 185″ for (0002) symmetric reflection and (10-12) skew reflection,respectively.A room temperature mobility of 850cm2/(V·s) is obtained for a 3μm thick GaN film.Gain guided and ridge geometry waveguide laser diodes are fabricated with cleaved facet mirrors at room temperature under pulse current injection.The lasing wavelength is 405.9nm.A threshold current density of 5kA/cm2 and an output light power over 100mW are obtained for ridge geometry waveguide laser diodes.