(Ga,Mn)As光调制反射光谱

室温下我们研究了稀磁半导体(Ga,Mn)As的光调制反射(PR)光谱,观测到来自样品的Franz-Keldysh振荡(FKO)信号。随着Mn原子浓度的增加,PR线形展宽,但是临界点E₀和E₀+Δ₀没有明显的移动。根据FKO振荡数据,计算得到样品表面电场强度随Mn原子掺杂浓度的增加而增强。测量到与Mn原子掺杂相关的杂质带,其能量位置离GaAs价带边~100 meV。根据样品的表面电场强度和表面耗尽层模型,估算样品的空穴浓度为~10¹⁷cm^-3,较低的空穴浓度可能与样品具有较低的居里温度有关,或测量的PR信号来自于样品中外延层的部分耗尽区域。     

低温分子束外延生长的GaMnAs反射光谱的低能振荡现象

通过傅里叶变换红外光谱和光调制反射光谱技术测量了不同Mn含量的低温分子束外延生长在GaAs衬底上的GaMnAs样品的反射光谱.在低于Ga(Mn)As带边的红外反射光谱和光调制反射光谱上观测到低能振荡现象.通过分析振荡产生的原因并使用双层界面反射模型拟合了红外反射光谱的低能振荡过程,拟合结果与实验相符.研究表明,反射光谱的低能振荡是由于GaMnAs中空穴浓度的变化导致GaMnAs中的折射率发生变化,GaMnAs与衬底GaAs之间的折射率差导致了不同Mn含量的GaMnAs材料的反射谱的低能振荡现象.测量了不同 关键词： GaMnAs 反射光谱 空穴浓度 折射率     

量子限制受主远红外电致发光器件的制备与测量

采用分子束外延技术生长GaAs/AlAs三量子阱,并在中间的GaAs阱中δ-掺杂浅受主杂质Be原子,制作出量子限制受主远红外Teraherz原型电致发光器件.实验上测量得到4.5 K时器件的电致发光谱（EL）和电传输特性（I-V曲线）.在EL发射谱中清楚地观察到222 cm^-1处宽的尖峰,这来源于Be受主奇宇称激发态到其基态的辐射跃迁,而非辐射弛豫过程则使发射谱的信号很弱.另外在I-V曲线中072和186 V的位置出现两个共振隧道贯穿现象,分别对应于中间δ-掺杂量子阱受主能级1s_3/2(Γ₆+Γ₇)到左边非掺GaAs量子阱中HH带,及右边非掺杂GaAs量子阱中HH重空穴带到中间掺杂GaAs量子阱中Be受主杂质原子奇宇称激发态2p_5/2(Γ₆+Γ₇)能级的共振隧穿. 关键词： 量子限制效应 电致发光 共振隧穿效应 δ-掺杂GaAs/AlAs三量子阱     

分子束外延生长AlGaAs/GaAs GRIN-SCH SQW激光器中高温陷阱的研究

应用深能级瞬态谱(DLTS)技术研究分子束外延(MBE)生长的AlGaAs/GaAs graded index separate confinement heterostructure single well(GRIN-SCH SQW)激光器的高温陷阱。样品的DLTS表明,在激光器的n-AlGaAs层里存在着高温(空穴、电子)陷阱,它直接影响着激光器的性能。高温空穴陷阱可能分布在x_Al =0.2→0.43和x_Al=0.43的n-AlGaAs层界面附近,而高温电子陷阱则可能分布在x_Al=0.43的n-AlGaAs层里x_Al值不连续的界面附近。高温电子陷阱的产生可能与AlGaAs层里的O有关。 关键词：     

超低温高电场下GaAs的电子太赫兹功耗谱的研究

利用自由空间太赫兹电光取样方法,测量了在高电场下,GaAs中受飞秒激光脉冲激发的电子所辐射出的太赫兹电磁波,发现从样品中辐射出的和电子加速度成正比的太赫兹电磁波电场强度E_THz（t）,表现出双极特性.通过分析GaAs中辐射出的太赫兹电磁波的傅里叶变换谱,首次实验上得到在阶跃电场下的GaAs的电子太赫兹功耗谱.研究发现,当电场小于50 kV/cm时,由电子谷间散射引起的负功耗（即增益）的截止频率ν_c,随着电场的增大而增大;当电场大于50 kV/cm时,负功耗的截止频率ν_c开始在750 GHz（10 K）附近饱和. 关键词： 太赫兹 非平衡载流子 功耗谱 谷间散射     

在C70固体/p-GaAs结构中的甚深深能级

发展了恒温电容瞬态数据处理方法，称新方法为恒温电容瞬态时间积谱(ICTTS).用ICT TS方法测量分析了C₇₀固体/p GaAs异质结的深能级，结果发现在C₇₀固体中存在两个很深的空穴陷阱，H C₁和H₂，它们的能级位置分别为Ev⁺⁰856eV和 Ev+1037eV. 关键词： 70')" href="#">C₇₀ 深能级 恒温电容瞬态     

高分辨傅里叶变换激光腔内吸收光谱方法：原理和应用

介绍了使用连续扫描方式工作的傅里叶变换光谱仪来探测激光腔内吸收光谱的原理,并探讨了傅里叶变换激光腔内吸收光谱方法测量光谱谱线和强度的工作方式.通过对大气中水汽在12450—12700cm^-1波段的高分辨吸收光谱的实际测量,检验了该方法的可靠性,并使用该方法测量了重水分子(D₂O和HDO)ν_OD=5伸缩泛频态光谱. 关键词： 激光光谱 高分辨振转光谱     

类金刚石和碳氮薄膜的电化学沉积及其场发射性能研究

利用电化学方法在室温下成功地沉积了类金刚石(DLC)薄膜和非晶CN_x薄膜，并 对制备条件进行了讨论.通过扫描电子显微镜、傅里叶变换红外光谱技术，分析了薄膜的表面形貌和化学结合状态.场发射测量结果表明：DLC膜和非晶CN_x的开启场分别为88和 10V/μm；并且在23V/μm的电场下，DLC膜和非晶CN_x膜的发射电流密度分别达到10 和037mA/cm². 关键词： 电化学沉积 类金刚石薄膜 x薄膜')" href="#">CN_x薄膜 场致电子发射     

磷掺杂纳米硅薄膜的研制

用PECVD薄膜沉积方法,成功地制备了磷掺杂纳米硅(nc-Si:H(P))薄膜.用扫描隧道电镜(STM)、Raman散射、傅里叶变换红外吸收(FTIR)谱、电子自旋共振(ESR)、共振核反应(RNR)技术对掺磷纳米硅进行了结构分析,确认了样品的微结构为纳米相结构.掺磷后膜中纳米晶粒的平均尺寸d减小,一般在25—45nm之间,且排列更加有序.掺磷nc-Si:H膜具有较高的光吸收系数,光学带隙在173—178eV之间,和本征nc-Si:H相同.掺杂nc-Si:H薄膜电导率在10^-1关键词：     

注氮GaAs中的深能级及其对自由载流子的补偿

详细研究了注氮n型GaAs中深的和浅的杂质缺陷的电学性质。深能级瞬态谱(DLTS)技术测量表明,能量为140keV和剂量为1×10¹³cm^-2的氮离子注入并经800℃退火30min的GaAs中存在四个电子陷阱,E₁(0.111),E₂(0.234),E₃(0.415),E₄(0.669)和一个空穴陷阱H(0.545),而在能量为20keV和剂量为5×10^{14关键词：}     

Detecting a true quantum pump effect

Reflectance measurements from p-type GaSb:Zn epitaxial films with different hole concentrations (10¹⁷–10¹⁸ cm^-3) have been investigated over the frequency region of 100–1000 cm^-1. A minimum broadening feature corresponding to the hole plasmon was observed in the reflectance spectra. The experimental infrared spectra were well fitted using a Lorentz-Drude dispersion model. The real part ε₁ of the dielectric function decreases with increasing hole concentration. However, the imaginary part ε₂ increases with hole concentration in the far-infrared region. This indicates that the acoustic- and optic-phonons mainly participate in the free carrier absorption processes. The hole mobility obtained from Hall-effect measurements is slightly larger than that derived from optical measurements and the average ratio of mobilities is estimated to be 1.33. Owing to overdamping effects, the upper branch of longitudinal-optical phonon plasmon (LPP) coupled modes was observed. The upper LPP⁺ frequency increases with hole concentration and it shows a transition from phonon-like to plasmon-like behavior. A theoretical analysis with solutions in the complex frequency plane describes these experimental results.     

Quasi-normal Modes of Rerssner-Nordström Black Hole

The minimum interval of event horizon area of Rerssner-Nordström black hole was calculated via using the loop quantum gravity theory. Based on the first law of black hole thermodynamics, the real part of quasi-normal modes frequency of the black hole was calculated. The expression of asymptotically quasi-normal mode frequency of Rerssner-Nordström black hole was deduced strictly. By analyzing the value of the minimum spin j _{m i n} , the two families of quasi-normal mode spectra of the charged black hole were obtained for j _{m i n} = 1/2 and j _{m i n} = 1 respectively. Our conclusion is in complete agreement with the analytical results of Hod. Our results provide the theoretical basis for the source of the real part of the quasi-normal mode frequency of the black hole.     

Optical response of saddle point excitons

The linear optical response of interband transitions near saddle points is studied within the framework of the effective mass approximation. The method is based on Stahl's configuration space theory. Unlike previous works the present treatment allows an unrestricted range of effective mass ratios, and it generates both real and imaginary part of the dielectric function. Spectra are calculated by numerical integration of a two dimensional second order partial differential equation. The results obtained for M₁ saddle points agree well with the observed lineshape of the E₁ peak in ZnTe.     

基于粒子群算法的有机半导体NPB传输特性辨识

为了研究有机半导体材料的载流子传输特性,制备了单层器件ITO/NPB/Ag,建立了该器件的理论导纳模型.利用正弦小信号频域测试法得到该器件在不同直流偏压下的频率特性样本.定义了同时包含有机半导体阻抗实部和虚部的模型参数辨识问题的目标函数,采用粒子群算法对包括载流子迁移时间τdc,色散度参数M和α在内的模型参数进行辨识.为了验证提出方法的有效性,建立了器件的等效电路模型,并用最小二乘算法辨识出等效电路的时间常数τc.实验上对1000 nm和1200 nm的单层器件进行频域测试,经计算发现τdc和τc之间具有相同的比例关系,通过对计算出的空穴迁移率μdc进行指数拟合发现,两种厚度的NPB器件的空穴迁移率与电场强度呈指数增加,且满足著名的Poole-Frenkel公式.     

Finite lifetime broadening of calculated X‐ray absorption spectra: possible artefacts close to the edge

X‐ray absorption spectra calculated within an effective one‐electron approach have to be broadened to account for the finite lifetime of the core hole. For methods based on Green's function this can be achieved either by adding a small imaginary part to the energy or by convoluting the spectra on the real axis with a Lorentzian. By analyzing the Fe K‐ and L_2,3‐edge spectra it is demonstrated that these procedures lead to identical results only for energies higher than a few core‐level widths above the absorption edge. For energies close to the edge, spurious spectral features may appear if too much weight is put on broadening via the imaginary energy component. Special care should be taken for dichroic spectra at edges which comprise several exchange‐split core levels, such as the L₃‐edge of 3d transition metals.     

Pr-substituted W-type barium ferrite: Preparation and electromagnetic properties

The W-type ferrites doped with Pr³⁺, BaCoNiPr_xFe_16−xO₂₇ (x=0-0.20), were prepared by a sol-gel method. The structure and electromagnetic properties of the samples are studied using powder X-ray diffraction, field emission scanning electron microscope, vibrating sample magnetometer and vector network analyzer. All the samples are hexagonal platelet-like W-type barium ferrite. These synthesized samples exhibit paramagnetism and strong magnetism. The saturation magnetization (Ms) increases with the increase of Pr³⁺ content. The real part of complex permittivity (ε′) decreases and the imaginary part (ε″) increases with Fe³⁺ replaced by Pr³⁺. The imaginary part of complex permittivity (μ″) increases and the real part (μ′) decreases after Pr³⁺ is doped. Furthermore, the doped Pr³⁺ improves the microwave absorbency.     

Dielectric response of SrTiO<Subscript>3</Subscript>–SrMg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>O<Subscript>3</Subscript> solid solutions in the terahertz–infrared range

The reflection and transmission spectra of ceramic samples of SrTiO₃–SrMg_1/3Nb_2/3O₃ solid solutions have been measured in the frequency range of 5–5000 cm^–1 and in the temperature range of 5–370 K. Based on these spectra, the spectra of the real ε'(ν) and imaginary ε''(ν) parts of the complex permittivity ε*(ν) have been simulated by the method of dispersion analysis. It has been found that the temperature evolution of the dielectric constant is entirely determined by the behavior of the soft mode.     

Determination of the asymmetry parameter of EFG tensor from moments of NQR nutation spectra in powders

A novel approach to determination of the asymmetry parameter of the EFG tensor from zero-field nutation NQR spectra of the spinI = 3/2 nuclei in powder samples is reported. The proposed theoretical treatment uses lineshape analysis of the nutation NQR spectra by the method of line moments. The analytical formulas for the lineshape of the powder nutation spectrum are given. It is shown that the asymmetry parameter can be determined from the second moment 〈ω²〉 and the frequency of only one singularity ω₂ of the nutation spectrum. It is also shown that the asymmetry parameter can be determined from the second and fourth spectrum moments alone. The method is successfully demonstrated for the simulated nutation NQR spectra of the spinI = 3/2 nuclei in powder samples.     

Quasinormal Modes of Clifton–Barrow Black Holes

In this paper, we study the theoretical quasinormal modes produced by scalar perturbations around a static, spherically symmetric black hole with exterior metric described by the Clifton–Barrow solution of R ^1+δ gravity. It is found that the δ-correction increases both the real and imaginary part of the quasinormal frequency. Compared with those of ordinary Schwarzschild black hole with the same size, the oscillating quasi-period of scalar perturbation of Clifton–Barrow black hole is remarkably short for the case of low multi-pole quantum number l, while the difference of the damping time scales is slight. However, in the large l limit, the relative differences of both real and imaginary part of quasinormal modes have the same amplitude.     

Dynamic properties of P4O6S and P4O7: P spin–echo and P MAS–NMR investigations

The rotational dynamics of P₄O₆S and P₄O₇ in the solid state were studied by means of ³¹P NMR spectra of spinning and static powder samples in the temperature range of 153–295 K and 295–388 K, respectively. All spectra were simulated to confirm the type of the motion and to extract the time scales as a function of the temperature. Good agreement between experimental and theoretical data was obtained on the basis of a three-site jump model. For P₄O₆S, the activation energy and the pre-exponential factor derived from the lineshape simulations amount to 51(2) kJ/mol and 6(3)·10¹⁵ s⁻¹. For P₄O₇, the spectral analysis yields an activation energy of 67(1) kJ/mol and a pre-exponential factor of 6(2)·10¹⁴ s⁻¹. The dynamic behavior was checked independently by lineshape analyses under both MAS and static conditions. Activation energies are consistent within the errors for the lineshape analyses. Additionally, we have analyzed spin–lattice relaxation measurements, which show the correct trends for the activation energies.