四方晶系应变Si空穴散射机制

基于Fermi黄金法则及Boltzmann方程碰撞项近似理论, 推导建立了(001)弛豫Si_1-xGe_x衬底外延四方晶系应变Si空穴散射几率与应力及能量的理论关系模型, 包括离化杂质、声学声子、非极性光学声子及总散射概率(能量40 meV时)模型. 结果表明: 当Ge组分(x)低于0.2时, 应变Si/(001)Si_1-xGe_x材料空穴总散射概率随应力显著减小. 之后, 其随应力的变化趋于平缓. 与立方晶系未应变Si材料相比, 四方晶系应变Si材料空穴总散射概率最多可减小66%. 应变Si材料空穴迁移率增强与其散射概率的减小密切相关, 本文所得量化模型可为应变Si空穴迁移率及PMOS器件的研究与设计提供理论参考.     

飞秒激光激发空气电离的阈值研究

报道在脉宽50fs—22ps，波长800nm脉冲激光作用下的空气电离阈值的研究结果.利用探测等离子体发光信号的方法，实验测量了激发空气电离所需的阈值激光强度.结果表明，当激光脉冲宽度从50fs增加到22ps时，阈值光强I_th从8.7×10¹⁴W/cm²下降到2.7×10¹³W/cm²；I_th经历了由迅速降低逐渐发展为缓慢降低的过程.在50fs—1p     

光系统ⅡChl分子能量传递超快光谱动力学

利用ICCD飞秒扫描成象和飞秒时间分辨光谱装置实验研究了高等植物捕光天线LHCⅡ三聚体和PSⅡ颗粒复合物的超快光谱动力学,经过吸收光谱和发射光谱分析,确定在LHCⅡ三聚体中至少存在7种Chl分子光谱特性,分别是Chlb_653/656^658.7、Chla_662.0^665.2、Chla/b_670/671^677.1、Chla_675.0^677.1、Chla_680/681^682.9、Chla_685.0^689.1和Chla_695.0^695.6.采用光强1013光子/cm²/脉冲激励浓度为30μg/mL的捕光天线LHCⅡ三聚体,在650nm到705nm谱段逐点探测分析处理,产生了2组短寿命组分210fs、520fs和5.2ps、36.7ps及2个长寿命组分1.8ns、2ns.最快的3个寿命210fs、520fs和5.2ps反映了三聚体Chlb分子向Chla分子的激发能传递过程;寿命36.7ps反映了Chla分子向相邻单体Chla分子的激发能传递过程;最长的2个寿命1.8ns和2ns是在三聚体中Chla分子通过中间体Chla分子辐射荧光,分别跃迁回基态的过程.获得的6个寿命组分有把激发能传递时间与Chla/b分子发射光谱相结合的特点.经拟合处理解析PSⅡ颗粒复合物光谱,得到3个组分谱,其峰值分别为686.8nm、692.2nm和694.9nm,与LHCⅡ比较分析,说明天然构型的PSⅡ有很强的吸收光能和有效传递光能的本领.     

HD+离子在两个超短脉冲激光场作用下的解离几率分布

本文报告HD⁺离子在波长λ=306.7nm的三倍频超短脉冲弱光场E₃和不同延时的二倍频超短脉冲强光场E₂作用下解离几率分布的定量计算结果。E₃和E₂的脉冲宽度均为10fs.E₃先行,E₂延时取0、4、8、12、16、20、24、28fs.计算结果用三维图表出。图中看到,沿相对动量坐标有三个峰,分别位于动量2.1×10^-18、4.4×10^-18、5.8×10^-18g·cm/s处,依次称为1号峰、2号峰、3号峰,位置各是λ=306.7nm的单光子能量、双光子能量、三光子能量消耗于解离能之后离子碎片具有相对动量。据分析,1号峰来源于E₂场引起的受激发射作用。     

应变Ge/Si1-xGex 价带色散模型

基于k·p微扰理论, 通过引入应变哈密顿量作为微扰, 建立了双轴应变Ge/Si_1-xGe_x价带色散关系模型. 模型适于任意晶向弛豫Si_1-xGe_x虚衬底上的应变Ge价带结构, 通过该模型可获得任意k方向应变Ge的价带结构和空穴有效质量. 模型的Matlab模拟结果显示, 应变Ge/Si_1-xGe_x价带带边空穴有效质量随Ge组分的增加而减小, 其各向异性比弛豫Ge更加显著. 本文研究成果对Si基应变Ge MOS器件及集成电路的沟道应力与晶向的设计有参考价值.     

磁场中耦合量子线的三阶非线性光学吸收率

本文研究了磁场中耦合量子线的三阶非线性光学吸收率,并且利用密度矩阵算符理论导出了三阶非线性光学吸收率的解析表达式.最后,以GaAs/Al_xGa_1-xAs耦合量子线为例作了数值计算,并绘出了三阶非线性光学吸收率与磁场B,光子能量h-ω以及间隔D之间的依赖关系.     

共轭低聚物中光生分子间电荷转移态的第一性原理研究

本文基于第一性原理中的Heyd-Scuseria-Ernzerh方法研究了单层In_1-xGa_xN的电子结构和光学性质.计算得到单层In_1-xGa_xN的能带结构和态密度（DOS）,发现随着掺杂比例的变化,体系带隙的变化范围是1.8~3.8 eV,表明通过Ga的掺杂可以实现体系带隙值的调节.并且还研究了单层In_1-xGa_xN的介电函数,折射率和吸收系数等光学性质,结果表明随着Ga掺杂浓度的增加,介电函数谱的主峰和吸收谱发生了显著的蓝移.此外,基于能带结构和态密度图谱,对单层In_1-xGa_xN的光学性质进行分析,预测这种材料独特的光学性质在纳米电子学和光学器件中会有广泛的应用.     

掺Er光纤飞秒激光器中高信噪比载波包络位相偏移频率获取的实验研究

在实验上分析了掺Er光纤光学频率梳中激光器与一级放大器之间光纤长度、 光纤扰动以及放大器抽运功率对倍频程光谱和载波包络位相偏移频率(f₀)信噪比的影响. 通过系统优化, 实现了40 dB信噪比的f₀输出, 为f₀的长期锁定和光纤光学频率梳的实现提供了技术保障.     

半导体材料AAl2C4(A=Zn, Cd, Hg; C=S, Se)的电子结构和光学性质

采用基于密度泛函理论的第一性原理方法, 对具有缺陷型黄铜矿结构的半导体材料A^ⅡAl₂C₄^Ⅵ(A=Zn, Cd, Hg; C =S, Se)的构型和电子结构进行研究, 并系统考察了各晶体的光学性质. 对于线性光学性质, 五种晶体在红外区和部分可见光区具有良好的透光性能, 其中HgAl₂S₄和HgAl₂Se₄晶体具有适中的双折射率. 在非线性光学性质方面, 该类晶体倍频效应较强, 理论预测得到的二阶静态倍频系数均较大(>20 pm/V). 体系的倍频效应主要来源于价带顶附近以S/Se 价p轨道为主要成分的能带向含有较多Al/Hg 价p成分的空带之间的跃迁. 通过与已商业化的AgGaC₂晶体光学性质的对比, 结果表明HgAl₂S₄和HgAl₂Se₄是一类性能优良的红外非线性光学晶体材料.     

向列型液晶中简并四波混频相位共轭的理论研究

研究向列型液晶中由光致分子重取向引起的简并四波混频光学相位共轭现象,着重讨论液晶薄膜厚度d、探测光与一泵浦光之间的夹角θ_ω以及光的入射面和液晶指向矢之间的夹角β对相位共轭光产生效率的影响.     

Heavy doping effects on donor-acceptor spectra of polar semiconductors at low temperatures

The heavy doping effects on donor-acceptor (DA)-pair spectra at small DA-pair distances R are investigated, basing on an effective screened impurity potential model given by Morgan and on the results of the R-dependent electron (hole)—longitudinal optical phonon interaction energy obtained by Kartheuser et al. It is suggested that the deviation of the electron—hole recombination energy by dense impurities (or at small R), found from the energy of the emitted photon for a zero-phonon transition, results from the band-gap narrowing effect.At large R, we have found that the energy gap of the pure ZnSe crystal is equal to 2.827 eV, in good agreement with observed results. Finally, at small R, our numerical results applied to ZnSe doped with ln and Li impurities are compared with other theories and with observed results.     

Impurity doping in silicon nanowires synthesized by laser ablation

Boron (B) or phosphorus (P) doped silicon nanowires (SiNWs) were synthesized by laser ablation. Local vibrational modes of B were observed in B-doped SiNWs by micro-Raman scattering measurements at room temperature. Fano broadening due to a coupling between the discrete optical phonon and a continuum of interband hole excitations was also observed in the Si optical phonon peak for B-doped SiNWs. An electron spin resonance signal due to conduction electrons was observed only for P-doped SiNWs. These results prove that B and P atoms were doped in substitutional sites of the crystalline Si core of SiNWs during laser ablation and electrically activated in the sites.     

Nonlocal screening, electron-phonon coupling, and phonon renormalization in metals

A method for calculating the phonon self-energy in metals arising from the coupling between phonons and electrons near the Fermi surface is developed. The essence of this scheme is the separation of the inter- and intraband parts of the electron polarizability. The intraband contribution provides extra screenings and is closely related to the electron-phonon coupling and phonon softening in metals. Applications of this scheme to phonons in MgB2 give excellent results when compared with experiments and previous theoretical work. In addition, both electron and hole dopings are found to reduce the renormalization effect of the E(2g) phonon mode, which indicates a weakened electron-phonon coupling in the doped systems.     

Photoluminescence measurements of the 1.55 eV band of Ge doped AℓxGa1−xAs

The photoluminescence of the 1.55 eV band of Ge doped A?_xGa_1?xAs, with x=0.30–0.33, grown by liquid phase epitaxy is presented. The broad shape was found to be due to a lattice relaxation upon optical transitions. Resonant modes with ?ω_q = 35±2 meV and ?ω_q = 45±2 meV are found for the optical band, yielding a zero phonon transition energy = 1.73±0.02 eV and a Franck-Condon shift = 0.17–0.20 eV for the optical center. The activation energy of thermal quenching yields an associated donnor binding energy of 0.17±0.04 eV. Possible mechanisms for the radiative transitions are discussed.     

纤锌矿相GaN空穴输运特性的Monte Carlo模拟研究

用全带多粒子Monte Carlo方法模拟纤锌矿相(Wurtzite)GaN空穴输运特性的结果. 用经验赝势法计算得到能带结构数据. 模拟包含了声学声子散射，光学声子散射，极性光学声子散射，压电散射，电离杂质散射及带间散射等散射机理. 计算得到了空穴沿3个主要对称方向上的空穴平均漂移速度和平均能量与电场强度的关系曲线，室温下漂移速度呈现饱和特性. 在所研究的电场范围内，最大平均漂移速度约为6×10⁶cm s^-1，最大空穴平均能量约为0.12eV, 这些值均比电子的相应参数低很多. 还给出了空穴的扩散迁移率与杂质浓度关系的模拟结果. 关键词： 蒙特卡罗 氮化镓 输运特性 能带结构     

Magneto-optics and strain effects in GaInAsAlInAs and GaInAsInP quantum wells

Transitions between the Landau levels of the lowest electron and hole sub-bands have been observed in the inter-band optical absorption of a modulation doped Ga_.47In_.53AsAl_0.48In_.52As superlattice and a Ga_0.3In_.7AsInP strained layer superlattice, in magnetic fields up to 16T. In the unstrained sample, the energies of transitions up to 250 meV above the GaInAs band gap were found to be well described by a parabolic model for the heavy hole band and the model of Bowers and Yafet for the conduction band. In contrast to previous work on undoped quantum wells, no Coulomb binding effects were observed in this lightly doped sample, and this is attributed to screening of the exciton. In the strained sample, the heavy hole sub-band was found to show highly non-parabolic structure, and this is believed to be due to the effects of biaxial strain on the valence band.     

p型导电掺In的SnO2薄膜的制备及表征

采用溶胶-凝胶提拉法成功地制备了p型导电掺In的SnO2薄膜.x射线衍射测试结果表明，掺In的SnO2薄膜保持SnO2的金红石结构.吸收谱测试结果表明，掺In的SnO2禁带宽度为3.8eV.霍尔测量结果表明，空穴浓度与热处理温度有很大的关系，525℃为最佳热处 理的温度.铟锡原子比在0.05—0.20范围内，空穴的浓度与In的含量有直接的关系，并随In含量的增加而增加. 关键词： SnO2 溶胶-凝胶法 p型导电     

Numerical evaluation of energy loss rate for hot carriers in quantum wells

Using the Fröhlich potential associated with realistic optical phonon modes in quantum well systems, the energy loss rates of hot electrons, holes, and electron–hole pairs are calculated, with special emphasis on the effects of carrier density, hot phonon population, quantum well width, and phonon dispersion on the hot-carrier relaxation process in quasi-two-dimensional systems.     

光子选通多重光谱烧孔中的光致填孔机制

报道了给体－受体电子转移型材料ｚｉｎｃ－ｔｅｔｒａｐｈｅｎｙｌｂｅｎｚｏｐｏｒｐｈｒｉｎ＋ｚｉｎｃ－ｔｅｔｒａｐｈｅｙｌ ｂｅｎｚｏｔｒｉｂｅｎｚｏｐｏｒｐｈｒｉｎ／ｐｈｙｄｒｏｘｙｂｅｎｚａｌｄｈｙｄｅ／ｐｏｌｙ（ｍｅｔｈｙｌ）ｍｅｔｈａｃｒｙｌａｔｅ的光子选通多重烧孔过程。结果表明要获得高质量的多重光谱孔，从短波往长波的逐次烧孔更为有效。其影响来自与波长有关的光致填孔现象，造成该填孔的主要机制     

Quantum confinement effects on the optical phonons of CdTe quantum dots

We present Raman-scattering results for CdTe nanocrystals in doped glasses which clearly show the confinement effects on the phonon spectra as a function of the quantum-dot size. We observed optical phonon modes, surface phonons and some of their overtone combinations. We show that the surface-phonon scattering intensity increases as the quantum-dot size decreases. Our results also show a decrease in the electron–phonon coupling as the nanocrystal size is decreased. These confinement effects are observed by changing the laser excitation energy, and thus by tuning to resonance with the optical transitions for quantum dots of different sizes within their broad size distribution in semiconductor-doped glasses.