中红外下半导体掺杂调制的表面等离子体透射增强效应

理论研究了平面电磁波通过n型重掺GaAs薄膜的透射谱.当GaAs薄膜两表面刻上亚波长的周期性沟槽结构时,透射谱在中红外波段出现了异常的透射增强现象.把这一现象归因于表面等离子体模式和波导模式的耦合.通过优化结构参数可以得到最大的透射效率.此外,发现随着掺杂浓度的升高,透射谱线中的透射峰逐渐向高频方向移动,最优化后透射峰值随掺杂浓度的升高而逐渐降低.这是由于掺杂浓度的改变,导致了不同的等离子体频率和电子碰撞频率,从而影响了激发模式和薄膜对电磁波的吸收. 关键词： 表面等离子体 掺杂半导体 增强透射 掺杂调制     

光子晶体对太赫兹波的调制特性研究

利用传输矩阵方法研究了掺杂半导体n-GaAs/聚碳酸脂一维光子晶体的太赫兹波透射谱.研究结果发现,与一般由两种介电材料组成的一维光子晶体不同,由于掺杂半导体中自由载流子对太赫兹波存在较强的吸收,所以这种材料组成的一维光子晶体除可形成光子带隙外,还可以增强n-GaAs对太赫兹波的透射.同时还提出了一种基于这种一维光子晶体的太赫兹波调制器,通过外加电压控制半导体中电子浓度的大小可实现对太赫兹透射波幅度的调制. 关键词： 掺杂半导体光子晶体 太赫兹波 太赫兹波的调制     

透射式指数掺杂GaAs光电阴极最佳厚度研究

通过研究指数掺杂GaAs光电阴极中光电子扩散漂移长度与均匀掺杂GaAs光电阴极中光电子扩散长度的差异,确定透射式指数掺杂GaAs光电阴极的最佳厚度范围为16—22 μm.利用量子效率公式对透射式指数掺杂GaAs光电阴极最佳厚度进行了仿真分析,发现厚度为20 μm时阴极积分灵敏度最大.外延生长阴极厚度分别为16和20 μm的两种透射式指数掺杂GaAs样品并进行了激活实验,测得样品的积分灵敏度分别为1228和1547 μA/lm,两者的比值为796%. 实验结果与仿真结果符合. 关键词： GaAs光电阴极 透射式 指数掺杂 厚度     

掺杂BaTiO3/SrTiO3多层膜与太赫兹波相互作用

掺杂半导体中的载流子吸收在THz波段非常明显,其相互作用研究是研制THz通信中的关键器件之一的基础。采用氟化氪（KrF）脉冲准分子激光烧蚀沉积（PLD）技术,制备了Ni掺杂BaTiO3/SrTiO3多层膜。基于辐射频率为3.09 THz、脉冲功率为10 mW量级的THz 量子级联激光器(QCL)光源研究了太赫兹波在Ni掺杂BaTiO3/SrTiO3多层膜中的传输,发现损耗主要是Ni颗粒的非共振吸收导致。     

含δ势垒的铁磁/半导体/铁磁异质结中的自旋输运和渡越时间

研究了含δ势垒的铁磁/半导体/铁磁异质结中自旋相关的透射概率和渡越时间,讨论了量子尺寸效应和Rashba自旋轨道耦合效应对隧穿特性的影响.研究结果表明：δ势垒的存在降低了自旋电子的透射概率,改变了透射概率的位相.Rashba自旋轨道耦合强度的增加加大了透射概率的振荡频率.不同自旋取向的电子隧穿异质结时,渡越时间随着半导体长度、Rashba自旋轨道耦合强度以及两铁磁电极中的磁化方向的夹角的变化而变化. 关键词： δ势垒')" href="#">δ势垒 铁磁/半导体/铁磁异质结 Rashba自旋轨道耦合效应 渡越时间     

BaBi1-xPbxO3体系的物理性质研究

采用固态反应法制备了一系列BaBi1-xPbxO3(x: 0～1)多晶并测定了其晶体结构和相应的物理性质.粉末法测得的X射线衍射所得的晶体结构与粉末中子衍射结果[1～2]一致,晶体经历了从单斜晶系(0≤x<0.1)、到正交晶系(0.1≤x< 0.65)、再到四方晶系(0.65≤x< 0.9)、最后到正交晶系(0.9≤x≤1.0)的转变.发现随着四价阳离子铅对铋的掺杂替代导致晶胞参数在半导体区域减小,而在超导区域振动变化,这归结于Bi3 和Bi5 被Pb4 的取代和呼吸模型Bi(Bb)O6的作用,从而证明了Bi两种价态的存在.电阻率的测量结果表明样品的电性与晶体结构和生长环境紧密相关,但氧缺陷不是主要因素.最佳掺杂区在x= 0.75,其超导临界温度约为9K.掺杂区0≤x≤0.3的样品既可用本征半导体解释,也可用3D变程跃迁解释.在半导体区用3D变程跳跃解释时,lnρ～T-1/4的斜率连续减小,说明掺杂改变了态密度或定域化长度.样品的金属-半导体转变可用交叠能带解释.拉曼光谱的测量结果表明改变入射激光的频率并不影响各拉曼峰的强度.随Pb的掺杂,BiO6八面体的呼吸模数逐渐减少,同时晶体的无序程度增强.超导温度与Bi(Bb)O6模的形变势的强弱无关,但受其频移的影响.     

指数掺杂GaAs光电阴极分辨力特性分析

通过建立和求解指数掺杂阴极中电子所遵循的二维连续性方程,得到了透射式指数掺杂阴极的调制传递函数表达式,并利用该表达式对阴极分辨力特性进行了理论计算和分析.计算结果显示,与均匀掺杂相比,指数掺杂能较明显地提高阴极的分辨力.当空间频率f在100—400 lp/mm范围时,分辨力的提高最为明显,如当f=200 lp/mm时,分辨力一般可提高20%—50%.与量子效率的提高相同,指数掺杂阴极分辨力的提高也是内建电场作用的结果. 关键词： 指数掺杂 内建电场 分辨力 调制传递函数     

印刷制作的双半导体底层碳纳米管薄膜阴极的稳定电子发射

应用带保护气进行烧结的方法,制作了一种双半导体底层碳纳米管薄膜阴极.利用烧结的银浆形成条形银电极,在条形银电极表面制作了具有相同宽度且平行排列的ZnO掺杂底层和TiO2掺杂底层,在掺杂底层上面制备了碳纳米管膜层.由于保护气的防氧化屏蔽,碳纳米管膜层中的碳纳米管未受损害,ZnO粒子和TiO2粒子也在烧结过程中得到了很好地保护,双半导体底层碳纳米管薄膜阴极获得更优的电子发射特性,且电子发射稳定性也得到有效增强.与普通条形银电极碳纳米管阴极相比,双半导体底层碳纳米管薄膜阴极能够将开启电场从2.09V/μm降低到1.91V/μm,将最大电子发射电流从1 653.5μA提高到2 672.9μA.在2.69V/μm电场作用下,普通条形银电极碳纳米管阴极的电子发射电流仅为421.1μA,而双半导体底层碳纳米管薄膜阴极的电子发射电流能够达到723.5μA.从发射电流稳定性实验曲线可以看出,双半导体底层碳纳米管薄膜阴极实现了稳定的电子发射,表明ZnO掺杂底层和TiO2掺杂底层能够应用于真空环境.利用数码相机获得了具有良好质量的发射图像,验证了双半导体底层碳纳米管薄膜阴极制作的可行性和适用性.     

Fe/Si多层膜的层间耦合与界面扩散

对以本征Si及重掺杂ｐ型和ｎ型Si作为中间层的Fe/Si多层膜的层间耦合进行研究，并通过退火，增大Fe，Si之间的扩散，分析界面扩散对层间耦合的影响. 实验结果表明，层状结构良好的制备态的多层膜，Fe，Si之间也存在一定程度的扩散，它是影响层间耦合的 主要因素，远远超过了半导体意义上的重掺杂，使不同种类的Si作为中间层的层间耦合基本 一致.进一步还发现，在一定范围内增大Fe，Si之间的扩散，即使多层膜的层状结构已经有了相当的退化，Fe/Si多层膜的反铁磁耦合强度基本保持不变. 关键词： Fe/Si多层膜 层间耦合 界面扩散     

非均匀波导中的最大声能流透射及鲁棒性分析

以变截面含可穿透散射体波导为模型,理论研究声波在非均匀波导中的最大透射问题.通过耦合简正波理论构建模态域内透射矩阵和水平波数矩阵,推导透射波能流的具体表达式,分析任意入射波的能流透射率随频率的变化,进而讨论任意给定频率下能够产生最大能流透射率的最佳入射波,并给出数组全透射声场算例.最佳入射波仅由可传播模态决定,与衰逝模态无关.利用衰逝模态不携带能流的特性,讨论衰逝模态对产生能流最大透射声场的影响,并分析最大能流透射的鲁棒性.在频率满足一定条件时,全透射声场可能表现出完美鲁棒性.文中所述方法可延伸至多种非均匀波导以分析其中的能流最大透射问题.     

Optical absorption bistability in quasi-one-dimensional peierls semiconductors

The optical absorption coefficient γ of a thin film of a Peierls semiconductor has been calculated in the dipole approximation for direct interband transitions as a function of intensity I and central frequency ω₀ of a quasi-monochromatic frequency spectrum near the lower optical transition edge. It is shown that the γ(I, ω₀) dependence is strongly nonlinear, and within a certain region of I and ω₀ variation, not single-valued, which indicates the onset of resonator-free optical bistability with increasing absorption.     

Nonlinear mixing of oppositely travelling surface plasmons

A theoretical treatment of the nonlinear mixing of two contra-directional surface plasmons of frequency ω₁ and ω₂ propagating on a semi-infinite metal surface is presented. The nonlinear interaction is analysed in terms of (a) nonlinear surface currents due to the breaking of inversion symmetry and the rapid variation of the normal electric field component at the surface, and (b) the nonlinear response of the electron gas in the bulk of the metal. These currents are treated as source terms for Maxwell's equations and electromagnetic fields are found which satisfy the driven wave equation and boundary conditions at the frequencies ω₁ ± ω₂. At the difference frequency ω₁ ? ω₂ the solution fields decay exponentially into both the air and the metal. However, at the sum frequency ω₁ + ω₂, coupling to transverse electromagnetic waves in both the air and the metal is predicted under appropriate wavevector and frequency conditions. The free-space radiation field is treated in detail and the feasibility of its experimental detection is discussed. No coupling to longitudinal bulk plasmons is predicted in this model of the nonlinear interaction.     

基于电子回旋共振-等离子体增强金属有机物化学气相沉积技术生长GaMnN稀磁半导体的研究

利用电子回旋共振-等离子体增强金属有机物化学气相沉积 (ECR-PEMOCVD)方法,采用二茂锰(Cp₂Mn)作为Mn源,高纯氮气作为氮源,三乙基镓(TEGa)作为Ga源,在蓝宝石(α-Al₂O₃)(0001)衬底上外延生长GaMnN稀磁半导体薄膜.反射高能电子衍射(RHEED)、X射线衍射(XRD)、原子力显微镜(AFM)表征了GaMnN薄膜的晶体结构和表面形貌.GaMnN薄膜均表现出良好的(0002)择优取向,表明制备的薄膜倾向于 关键词： GaMnN薄膜 稀磁半导体 铁磁性 居里温度     

Quantized longitudinal exciton-polaritons in periodic metal–semiconductor nanostructures

We theoretically investigate the optical properties of one-dimensional photonic crystals composed of two alternating layers, namely a semiconductor film and a metallic one. The nonlocal optical response of the semiconductor is here described by using a resonant excitonic dielectric function, whereas the local response function of the metal film is modeled with Drude formula. We calculate optical spectra of the metal–semiconductor 1D photonic crystal for both s- and p-polarization geometries. In both cases the spectra exhibit a rich resonance structure due to the coupling of size-quantized excitons inside the semiconductor film with light. We show the difference between s- and p-polarization reflectivity as the angle of incidence is increased. In the p-polarization geometry, besides transverse exciton-polariton modes, longitudinal polarization waves are excited producing additional spectral resonances. The spectra become radically different when the frequency corresponding to the minimum of the first photonic pass-band is close to the exciton resonance, since such a frequency is distinct for s- and p-polarized modes. We also show how reflectivity spectra for both polarizations are modified with varying the metal filling fraction which controls the width of the gap below the lowest frequency band.     

Specific features of infrared absorption in films materials subjected to a magnetic field

The reflection spectra and magnetorefractive effect (MRE) of metal (Co, CoFe), semiconductor (Si, GaAs), and granular and amorphous Co₃₀Ag₇₀ and Co₅₉Fe₅Ni₁₀Si₁₁B₁₅ films are studied in the IR spectral region at λ=2.5–25 μm. It is found that the IR optical properties of the ferromagnetic metal films can be described with regard to light absorption due to electron transitions in the two spin systems. The MRE is found to occur in both the ferromagnetic (Co, CoFe) and semiconductor (Si, GaAs) films. The amplitude and shape of the MRE are determined for the p and s polarizations of light. It is shown that, to a first approximation, the IR optical properties of the films with giant magnetoresistance can be described by the Drude theory, while the MRE is explained on the basis of a modified Hagen-Rubens relation. Variations in the IR reflection of semiconductor or amorphous metal films in the magnetic field are found to depend on the degree of polarization of localized electron states at the Fermi level.     

On the optical absorption due to particle-hole excitations in thin metal films

We present here a qualitative discussion on the optical absorption due to particle-hole excitations in thin metal films. We show that in sufficiently thin films, such excitations yield resonant absorption, when P-polarized light is obliquely incident on the metal surface. For instance, for frequency ω #62; ε_F where ε_F is the Fermi-energy, such resonances occur whenever ω satisfies the condition ω/ε_F = (1 + nπ/dq_F)² - 1, where n = 1,3,5,…,q_F is the Fermi wave-vector and d is the thickness of the film. The experimental observability of this effect is also discussed.     

Electrical metal contacts to atomically thin 2H-phase MoTe2 grown by metal–organic chemical vapor deposition

We grow atomically thin molybdenum ditelluride (MoTe₂) films on a SiO₂/Si substrate by means of metal–organic chemical vapor deposition (MOCVD). Our Raman spectroscopy measurements reveal the formation of 2H-phase MoTe₂ films. Further, transmission electron microscopy and X-ray photoelectron spectroscopy studies indicate a three-atomic-layer structure and the surface element composition of MoTe₂ films. In this study, we mainly focus on the influence of metal contacts attached to the films on their electrical performance. We fabricate 2H-phase-MoTe₂-based field-effect transistors (FETs) with various metal contacts such as titanium/gold, nickel and palladium, which present p-type semiconductor properties. We also examine the influence of the work functions of the contact metals on the electrical properties of three-atomic-layer-MoTe₂-based FET devices. For a p-type MoTe₂ semiconductor, higher work functions of the contact metals afford narrower Schottky barrier heights (SBHs) and eventually highly efficient carrier injection through the contacts.     

Epitaxial growth La0.67Ca0.33MnO3 thin film by radio frequency sputtering method

Perfect epitaxial growth of La_0.67Ca_0.33MnO₃ (LCMO) thin film has been achieved on (1 0 0) LaAlO₃ (LAO) single crystal substrate by radio frequency sputtering method. X-ray diffraction (XRD) and electron diffraction analysis indicates that La_0.67Ca_0.33MnO₃ film grows epitaxially on LaAlO₃ along [1 0 0] direction of the substrate. The resistivity variation with temperature of the film shows a sharp metal to semiconductor transition peak around 253 K, which is close to that of the target. The magnetoresistance (MR) also reveals high quality epitaxy film characteristic at low temperatures and near the metal to semiconductor transition temperature.     

Electrical,optical and structural properties of pure and gold-coated VO2 thin films on quartz substrate

In the present study, vanadium dioxide films were grown on quartz glass substrate by reactive KrF laser ablation technique using a vanadium dioxide target. The gold films of various thicknesses were then deposited on the VO₂ film by sputtering technique. Films were characterized by X-ray diffraction to determine crystallography, by four-point probe to determine the electrical property and by double-beam spectrophotometry to determine optical reflection and transmission behaviour in the 200–2500 nm spectral region. The resistance per square of VO₂ thin film decreases by two orders of magnitude across the metal insulator transition (MIT). The optical transmittance and reflectance exhibits, strong temperature dependence in the infrared region without a significant change in the visible region for VO₂ thin films. The presence of gold layer on VO₂ films significantly reduces the resistance per square, the critical temperature and percentage transmittance of the materials.     

Plasma resonance in granular silver films deposited on rough surfaces of NaCl and KCl single crystals

Granular silver films deposited on rough NaCl and KCl single-crystal surfaces exhibit, besides the low-frequency plasma-resonance band induced by the light-wave field and the field generated by the grain dipoles, a second, high-frequency plasma-resonance band, which is excited only by the light-wave field at the frequency ω₀ of the natural electron vibrations in the grains. The dielectric constant due to interband transitions was calculated from the known plasma frequency and the dielectric constant of the medium surrounding thegrains, the plasma frequency ω_p of the granular films, and the measured frequency of the maximum of surface plasmon vibrations in solid films. The results obtained agree with the data quoted by other authors.