Ti缓冲层及退火处理对Si(111)基片上生长的ZnO薄膜结构和发光特性的影响

采用反应磁控溅射法在Si（111）基片上制备了带有Ti缓冲层的高c轴取向ZnO薄膜.通过X射线衍射分析和光致荧光光谱测量,研究了Ti缓冲层厚度和退火处理对ZnO薄膜结晶质量和光致荧光特性的影响.研究结果表明,Ti缓冲层的引入可以有效改善Si基片上ZnO薄膜的发光性能,但缓冲层存在一个最佳的厚度.薄膜应力是影响ZnO薄膜紫外荧光发射性能的重要因素,较小的残余应力对ZnO薄膜的紫外荧光发射是有利的,残余应力的存在可以改变ZnO薄膜紫外荧光发射能量.随着退火温度的增加,薄膜中的张应力增大,导致带隙宽度减小以及激子复合跃迁峰逐渐向低能方向移动. 关键词： ZnO薄膜 缓冲层 退火处理 应力分析     

γ-LiAlO2上a面ZnO薄膜的光谱特性研究

利用激光脉冲沉积(PLD)技术在(302)γ-LiAlO₂衬底上成功生长了非极性的a面(1120)ZnO薄膜,光致发光谱(PL)带边发射峰半峰宽仅为115meV.研究了非极性ZnO薄膜光谱特性的面内各向异性,发现随着入射光偏振方向改变,在偏振透射光谱上,吸收边移动了20meV,这与A、B激子和C激子的能量差一致;而在拉曼光谱上,激发光偏振方向的改变导致E₂模式的强度发生明显改变. 关键词： 非极性ZnO 2')" href="#">γ-LiAlO₂ PLD     

变分方法研究ZnO量子点中激子的基态特性

ZnO是一种新型宽禁带直接带隙Ⅱ-Ⅵ族半导体材料,室温激子束缚能高达60meV,远大于室温热离化能(26meV),因此ZnO是适于室温或更高温度下使用的高效紫外光电材料。ZnO半导体量子点材料与体材料相比具有崭新的光电特性,特别在紫外激光器件方面,与ZnO的激子特性密切相关,因此理论上对ZnO量子点中激子的基态特性进行研究就显得十分必要。采用有效质量近似(EMA)方法,提出新的比较简单的尝试波函数,对ZnO量子点中激子的基态特性进行了计算。计算结果与实验结果基本吻合,说明我们的计算结果比较真实、有效。对变分参数K_e、K_h,归一化常数N_e、N_h以及波函数ψ随粒径变化关系进行了计算。计算结果表明,当量子点半径较小(r≤4.0a_B)时,激子的波函数ψ变化非常迅速,而由于此时量子点具有很大的比表面积,因此量子点所处的环境、体内的缺陷、杂质会对其产生非常强烈的影响,同时其表面(界面)的介质会对其基态特性产生影响,因此对量子点进行有效的修饰与掺杂以减少其表面缺陷及表面悬键,减少无辐射复合与界面发射是非常必要的。     

磁控溅射制备ZnO薄膜及其声表面波特性

通过射频磁控溅射技术在GaAs，Au/GaAs，Si和玻璃基片上成功制备了ZnO多晶薄膜，利用X射线衍射对ZnO薄膜的取向、结晶性进行了表征，结果表明ZnO薄膜呈完全c轴取向，Au缓冲层可以有效地改善ZnO薄膜的晶体质量，X射线摇摆曲线结果表明ZnO(002)衍射峰的半高宽仅为2.41°，同时发现Au缓冲层的结晶质量对ZnO薄膜的c轴取向度有很大影响，通过扫描电子显微镜对ZnO/GaAs和ZnO/Au/GaAs薄膜的表面形貌进行了观测，利用网络分析仪对IDT/ZnO/GaAs薄膜的声表面波特性进行了测量. 关键词： ZnO薄膜 X射线衍射 声表面波     

高质量纳米ZnO薄膜的光致发光特性研究

报道了利用低压-金属有机物化学气相沉积技术生长纳米ZnS薄膜，然后，将ZnS薄膜在氧气中于800℃温度下进行热氧化制备高质量纳米ZnO薄膜.x射线衍射结果表明，纳米ZnO薄膜具有六角纤锌矿多晶结构.室温下观察到一束强的紫外(3.26 eV) 光致发光和很弱的深能级发射.根据激子峰的半高宽度与温度的关系确定了激子-纵向光学声子（LO）的耦合强度（ГLO）.由于量子限域效应使ГLO减少较多. 关键词： 光致发光 热氧化 激子 纳米ZnO薄膜     

TiO2/ZnO纳米薄膜界面热导率的分子动力学模拟

采用平衡分子动力学方法及Buckingham势研究了金红石型TiO₂薄膜与闪锌矿型ZnO薄膜构筑的纳米薄膜界面沿晶面[0001](z轴方向)的热导率.通过优化分子模拟初始条件中的截断半径r_c和时间步后,计算并分析了平衡温度、薄膜厚度、薄膜截面大小对热导率的影响.研究表明,薄膜热导率受薄膜温度和厚度的影响很大,当温度由300 K升高600 K时,薄膜的热导率逐渐减小;当薄膜厚度由1.8 nm增大到5 nm时,热导率会逐渐增大;并在此基础 关键词： 热导率 分子动力学 2/ZnO纳米薄膜界面')" href="#">TiO₂/ZnO纳米薄膜界面 数值模拟     

变分法计算ZnO量子点中激子的基态能

ZnO是一种新型宽禁带直接带隙Ⅱ-Ⅵ族半导体材料,室温激子束缚能高达60meV,远大于室温热离化能(26meV),因此ZnO是适于室温或更高温度下使用的高效紫外发射材料。ZnO半导体量子点材料与体材料相比具有崭新的光电特性,特别在紫外激光器件方面,与ZnO的激子特性密切相关,因此理论上对ZnO量子点中激子的基态能(束缚能)的研究就显得十分必要。采用有效质量近似(EMA)方法,提出新的比较简单的尝试波函数,并用变分法对ZnO量子点的激子基态能进行了计算。将计算结果与我们用固态热分解法制备的ZnO量子点的实验结果进行了比较,发现与实验结果非常吻合;与Y．Kayanuma的理论计算结果进行了比较,二者的计算结果也基本一致。说明选取的尝试波函数简单有效,可用于计算其他半导体量子点材料,具有一定的实用价值。     

掺AlZnO纳米线阵列的光致发光特性研究

采用化学气相沉积方法，以金做催化剂，在Si (100)衬底上制备了掺AlZnO纳米线阵列.扫描电子显微镜(SEM)表征发现ZnO纳米线的直径在30nm左右.X射线衍射(XRD)图谱上只存在ZnO的(002)衍射峰，说明ZnO纳米线沿c轴择优取向.掺AlZnO纳米线阵列的室温光致发光(PL)谱中出现了3个带边激子发射峰：373nm，375nm，389nm.运用激子理论推算出掺AlZnO纳米线的禁带宽度为3.343eV ，束缚激子结合能为0.156eV；纯ZnO纳米线阵列PL谱中3个带边激子发射 关键词： 光致发光 化学气相沉积(CVD) 激子 ZnO纳米线阵列     

分子束外延生长的ZnO压电薄膜及其声表面波器件特性

用RF-MBE在蓝宝石(0001)衬底上引入MgO和低温ZnO双缓冲层生长了ZnO薄膜,并制备了声表面波器件。在ZnO薄膜中,仅观测到(0002)面的XRD,且衍射峰增强,半高宽减小,表明ZnO薄膜c轴取向性更好,晶体结构更优。室温下自由激子吸收峰更尖锐和吸收边更陡峭以及仅观测到自由激子发光,且发光线宽变窄、发光强度变大,表明ZnO薄膜缺陷密度减小,薄膜质量提高。测得该ZnO压电薄膜的电阻率高达4×10⁷ Ω·cm,其声表面波的速度高达5 010 m/s。     

ZnO/Ag/ZnO多层结构薄膜的光电性质

通过磁控溅射方法生长了不同银层厚度的ZnO/Ag/ZnO多层结构的薄膜,并对其形貌、光吸收谱、光致发光和光响应特性进行了比较研究.结果表明ZnO薄膜中银薄层的加入使得光致发光的强度增强.银层厚度为6 nm样品制成的器件在350 nm处的光响应度为0.06 A/W,相对于ZnO薄膜提高了一个数量级.而当银层厚度达到15 ...     

Exciton effects in armchair graphene nanoribbons

We have studied the exciton effects in armchair graphene nanoribbons systematically, using the nonorthogonal tight-binding model supplement by the long-range Coulomb interactions. It is found from our calculations that the excitation energies, the exciton binding energies and the exciton wave function sizes of the E ₁₁ and E ₂₂ excitons all exhibit oscillation as a function of the ribbon width. And there is a phase shift of π between the oscillation of the E ₁₁ and E ₂₂ excitons.     

Fractional-dimensional approach for excitons in GaAsfilms on AlxGa1-xAs substrates

Binding energies of excitons in GaAs films on Al_xGa_1-xAs substrates are studied theoretically with the fractional-dimensional approach. In this approach, the real anisotropic “exciton+film” semiconductor system is mapped into an effective fractional-dimensional isotropic space. For different aluminum concentrations and substrate thicknesses, the exciton binding energies are obtained as a function of the film thickness. The numerical results show that, for different aluminum concentrations and substrate thicknesses, the exciton binding energies in GaAs films on Al_xGa_1-xAs substrates all exhibit their maxima with increasing film thickness. It is also shown that the binding energies of heavy-hole and light-hole excitons both have their maxima with increasing film thickness.     

Binding energies of negatively charged excitons in quantum disks

The Hamiltonian of a negatively charged exciton X⁻ (trion) in a quantum disk with parabolic confinement has been diagonalized to obtain the binding eigenenergy values of the L1 states as a function of the electron-to-hole effective mass ratio and the disk radius. It is found that a negatively charged exciton X⁻ in a quantum disk may have the second bound state with orbital angular momentum L=1 and the triplet state of the two bound electrons.     

Photon-field-shape effects on Rabi splitting energies in CuCl microcavities

We have investigated the photon-field-shape effects on Rabi splitting energies in CuCl microcavities with HfO₂/SiO₂ distributed Bragg reflectors (DBRs). The CuCl active layer was prepared by vacuum deposition, while HfO₂ and SiO₂ layers were prepared by rf magnetron sputtering. The photon-field shape was tuned to a node-type or an antinode-type by changing the order of the refractive indices in the DBR. In order to control of the Rabi splitting energies, the active-layer thickness was changed from λ/12 to 9λ/20. In angle-resolved reflectance spectra at 10 K, three cavity polaritons resulting from the strong coupling between the Z₃ and Z_1,2 excitons and cavity photon were clearly detected. We estimated the energies of the exciton-photon interaction, the so-called vacuum Rabi splitting energies, from the analysis of the cavity polariton dispersions using a phenomenological Hamiltonian for the strong exciton-photon coupling. The active-layer-thickness dependence of the Rabi splitting energies are explained by a semi-quantitative analysis taking account of the overlap between the exciton and photon-field wave functions. We have demonstrated that the photon-field shape drastically affects the active-layer-thickness dependence of the Rabi splitting energies.     

The influence of different doping elements on microstructure, piezoelectric coefficient and resistivity of sputtered ZnO film

ZnO film is attractive for high frequency surface acoustic wave device application when it is coupled with diamond. In order to get good performance and reduce insertion loss of the device, it demands the ZnO film possessing high electrical resistivity and piezoelectric coefficient d₃₃. Doping ZnO film with some elements may be a desirable method. In this paper, the ZnO films undoped and doped with Cu, Ni, Co and Fe, respectively (doping concentration is 2.0 at.%) are prepared by magnetron sputtering. The effect of different dopants on the microstructure, piezoelectric coefficient d₃₃, and electrical resistivity of the film are investigated. The results indicate that Cu dopant can enhance the c-axis orientation and piezoelectric coefficient d₃₃, the Cu and Ni dopant can increase electrical resistivity of the ZnO film up to 10⁹ Ω cm. It is promising to fabricate the ZnO films doped with Cu for SAW device applications.     

Effect of different site energies on polaronic properties

A two-site single polaron Holstein model is studied in presence of a difference in bare site energies (epsilon_d=epsilon₂-epsilon₁) using the perturbation theory with the variational modified Lang-Firsov (MLF) phonon basis. The polaronic ground-state wave function is calculated up to the fifth order of perturbation. The effect of epsilon_d (acts as a strength of diagonal disorder) on the polaron crossover, polaronic kinetic energy, oscillator wavefuncion and polaron localization are studied. Considering a double-exchange Holstein model with finite epsilon_d, role of disorder on the properties of the double-exchange system is also discussed.     

Exciton effects on the refractive index and optical absorption in wurtzite quantum wells via a fractional-dimensional space approach

The optical refractive index changes and absorption coefficients of quantum wells (QWs) are theoretically investigated with considering exciton effects within the framework of the fractional-dimensional space approach. The exciton wave functions and bound energies are obtained as a function of spatial dimensionality, and the dimension increases with the well width increasing. Then optical properties are obtained by using the compact-density matrix approach and an iterative method. Numerical results are presented for wurtzite ZnO/Mg_xZn_1−xO QWs. The calculated results show that the changes of refractive index and absorption coefficients are greatly enhanced due to the quantum confinement of exciton. And the smaller the QW width (dimension) is, the larger influence of exciton on the optical properties will be. Furthermore, the exciton effects make the resonant peaks move to a lower energy. In addition, the optical properties are related to the QW width, the incident optical intensity and carrier density.     

Correlation energies of many-body complexes in biased InAs/GaAs quantum dots

The aim of this work is to analyze theoretically the correlation energies for neutral, positively, negatively charged exciton and bi-exciton. So, we propose a model consistent with experimental observations that is small InAs truncated pyramids with circular base lying on wetting layer, both buried into GaAs matrix.In a first step and in contrast to other works, we are able to evaluate coulombic interactions between electron and hole, two electrons and two holes by perturbative method at the second order. In a second step, the correlation energies of many-body complexes X, X^-, X⁺ and XX are investigated as a function of quantum dots basis radius r_c and the applied electric field.Our main goal is to provide realistic estimation for the correlation energies of excitons, charged excitons and bi-excitons while retaining at the same time a transparent formalism, which could easily be transposed to structures of actual interest.The present work provides evidence of the stability of excitons, charged excitons and bi-excitons in InAs/GaAs quantum dots. Calculated correlation energies of many-body complexes are consistent with those reported by recent photoluminescence measurements.     

Theoretical analysis of the astrophysical S-factor for the capture reaction α + d → 6Li + γ in the two-body model

Theoretical estimates for the astrophysical S-factor and the rate of the reaction d(α, γ)⁶Li were obtained on the basis of the two-body model involving an α−d potential that has a simple Gaussian form and which describes correctly S-, P-, and D-wave phase shifts, the binding energy, and the asymptotic normalization coefficient for the S-wave bound state. The wave functions for the bound and continuum channels were calculated with the aid of the highly precise Numerov algorithm. The results for the contributions of the E1 and E2 transition components reveal a good convergence as the upper limit in the effective integrals increases up to 40 fm. The results obtained for the astrophysical S-factor and the rate of the reaction d(α, γ)⁶Li in the temperature range of 10⁶ K ≤ T ≤ 10¹⁰ K agree well with the results of the calculations performed by A.M. Mukhamedzhanov and his coauthors [Phys. Rev. C 83, 055805 (2011)] by using the known asymptotic form of the wave function at low energies and a complicated two-body potential at higher energies.

     

The effect of spatial dispersion on the attenuation of exciton polaritons in semiconducting films

We calculate the effective light absorption coefficient K(ω) and the frequency-integrated absorption I = ∫ K(ω) dω caused by spatially dispersive excitons in a semiconductor film. A sharp decrease of I is found for small masses and long lifetimes of the exciton. Oscillations of I as a function of thickness are also reported.