Ⅲ-Ⅴ族化合物中氮束缚激子发光的动力学研究

用发光动力学的分析方法,研究了Ⅲ—Ⅴ族化合物中N束缚激子的发光强度与温度的关系,得到的理论公式与实验结果符合得较好。我们的分析指出,由于无辐射能量传递的存在,束缚激子的△J=2跃迁的发光效率低于△J=1跃迁的发光效率,致使低温(T<50K)下束缚激子的发光强度可能随温度的下降而变弱。另外,N杂质对自由激子再俘获的可能性的大小直接影响束缚激子发光的热猝灭过程:束缚激子可能因热离解成自由激子或自由的电子和空穴。我们找到了区分这两类情况的条件。     

MBE生长的掺Be p-GaAs的光荧光谱

本文报道利用国产分子束外延(MBE)设备和Be元素生长的p-GaAs的低温光荧光谱,观察到FE,(D°,X),(A°,X),(D+,X)等束缚激子发光,判断外延层有较好的质量。在1.503～1.515eV之间观察8条与缺陷有关的(d,x)发光线。仔细分析了与Be,Ge受主有关的(BA)和(DA)发光现象。     

氮化镓外延单晶中束缚激子辐射复合的偏振特性

研究发现,氮化镓外延单晶中束缚于中性施主中心和受主中心上的束缚激子BED°和BEA°的复合发光,具有偏振特性。这种偏振特性,会随激发光的强度发生变化。当激发光的强度在104W/cm2和106W/cm2间变化时,偏振度首先以二次方的规律随激发光强的增强而增加,而后超于饱和。本文首先用单轴晶体中介电函数的各向异性解释了荧光固有偏振度的起因,继而采用束缚激子间相互作用的电偶极子模型解释了荧光偏振度随激发光光强的变化规律。     

在正向电压激发下ZnSe MIS二极管的自由激子发光

研究了最低温度为20~30K时,在正向电压激发下ZnSe MIS二极管的激子发光光谱,在这一温度下,二极管有可能通过足以产生发光的电流.对于利用通常气相技术生长的高纯晶体所制备的二极管,其电致发光几乎完全由Γ8→Γ6自由激子发光的1LO和2LO声子伴线所组成.根据Gross等人的半经典理论,讨论了两个谱带的形状.结果是谱带的宽度和不对称性归结为激子服从Maxwell-Boltzmann分布,其有效激子温度接近于晶格温度.     

带有电子-双声子相互作用的一维铁磁性介观环的非经典本征态和非经典本征持续电流

在一维铁磁性织构介观环的基础上, 计及电子-双声子相互作用, 介入了三项非经典效应抑制电子-单声子相互作用引起的量子涨落效应: 1) 跳步电子-单声子相干态关联效应;2) 由压缩相干态引起的声子压缩态-单声子相干态间过程关联效应;3) 声子位移-声子压缩态的表象关联效应．从结果来看, 电子-双声子相互作用明显加强了压缩效应(增大压缩参量), 而跳步电子-单声子相干态关联效应引起本征能量大幅度下降, 持续电流大幅度增加．特别是介入了声子压缩态-单声子相干态间过程关联效应后, 声子压缩参量远大于理想压缩态相应的压缩参量, 有效地抑制了Debye-Waller(D-W)效应．当声子压缩态-单声子相干态间过程关联与声子位移重整化效应结合在一起时, 声子场的压缩将更大幅度地增加, D-W效应(参量w_ph)将更大幅度地减小, w_ph << w_ph⁽⁰⁾, 从而极大幅度地抑制了电子-单声子相互作用导致的量子涨落效应. 这样一来, 非经典态本征能量E_n极大幅度地下降, E_n << E_n⁽⁰⁾, 与此同时, 本征持续电流振幅I_n 则极大幅度地增大, I_n >> I_n⁽⁰⁾.     

黄-里斯因子及其在阐释固体有关光学性质的关键作用

1950年黄昆先生与A.Rhys(里斯,黄昆先生夫人,中文名李爱扶)发表了F-中心的光吸收与非辐射跃迁理论的论文,这一论文被公认为是处理电子-声子互作用在固体缺陷光吸收的先驱开创性量子理论工作,其中首先由黄昆先生所推导和明确的一个用于表征电子-声子耦合强度的无量纲因子,被广泛采用和推崇为黄-里斯因子(Huang-Rhys factor),也被简称为S因子.本文试图总结黄-里斯因子的物理内涵,以及它在阐释几种固体有关光学性质中的关键作用,包括在深缺陷中心发光以及带边浅杂质束缚激子发光中的支配作用.研究发现,在不同性质的固体材料中,电子(激子)-声子耦合强度可以分为极弱耦合(黄-里斯因子远远小于1)、中等耦合(黄-里斯因子在1—5之间)以及强耦合(黄-里斯因子远远大于1)等几种情况.限于篇幅及个人理解,本文仅讨论GaN各种带边激子、二维单原子层半导体激子、无机卤族钙钛矿纳米晶片激子以及金刚石单晶中NV复合中心等极弱及中等强度耦合等几种情况,以纪念黄昆先生诞辰百周年.     

高密度激发下CdS单晶的自由激子发光

本文首次在77K温度的电致发光光谱上,观测到了自由激子和自由激子(Ex-Ex)散射的发射带P。根据半经典理论,得到CdS单晶在高激发密度下的激子有效温度高于晶格温度。并且在77K温度下,通过氮分子激光器3371Å谱线的激发,观察到了Ex-Ex散射的P带的受激发射现象。     

非对称方势阱中的激子及其与声子的相互作用

采用类LLP(Lee-Low-Pines)变换和分数维变分法,在讨论有限深非对称方势阱Ga_1－xAl_xAs/ GaAs/Ga_0.7Al_0.3As的分数维基础上,计算了其中激子的基态能量以及声子对其影响,随着势阱宽度增加,激子能量先减小后增大,出现一个最小值.讨论了一侧势垒高度变化对分数维、激子基态能量的影响,并发现声子作用使得激子能量明显增大.另外,非对称方势阱中的激子结合能随阱宽的减小而增     

应变纤锌矿ZnO/Mg_xZn_(1-x)O柱形量子点中离子受主束缚激子的光学性质

在有效质量近似下,考虑内建电场效应,采用变分法详细研究了受限于纤锌矿Mg_xZn_(1-x)O/ZnO/Mg_xZn_(1-x)O圆柱形应变量子点中离子受主束缚激子(A~-,X)的带间光跃迁吸收系数随量子点尺寸、Mg含量和离子受主杂质中心位置的变化情况,并和离子施主束缚激子(D~+,X)及自由激子进行了比较.结果表明:随着量子点尺寸的减小,(A~-,X)的光跃迁吸收强度增强,吸收曲线向高能方向移动,出现蓝移现象.随着Mg含量增加,(A~-,X)的光跃迁吸收曲线蓝移,且吸收强度减弱.随着离子受主杂质从量子点的左界面沿材料生长方向移至量子点的右界面,光跃迁吸收曲线向低能方向移动,出现红移现象.此外,与离子施主束缚激子(D~+,X)相比,随着沿材料生长方向掺入杂质位置的变化,光跃迁吸收曲线移动的方向相反.但不管是掺入离子受主杂质还是离子施主杂质,当离子杂质从量子点的左异质界面沿材料生长方向移至右异质界面时,光跃迁吸收峰的移动量大致相同.     

GaPN混晶的瞬态发光特性

通过对GaP1-xNx混晶的瞬态发光特性的研究,揭示了在低组分下N杂质从NNi对束缚激子的特性逐渐向高组分下形成GaP1-xNx混晶的杂质带的演变。在较低组分下,样品的发光由NNi对束缚激子及其声子伴线构成,从NN1到NN4的衰减时间分别在90～30ns变化。当组分提高到x～1．3％以上时,样品的发光呈现出一个宽带,并按单指数规律衰减,辐射复合寿命大约在数十个纳秒量级,且随着N组分的增加,寿命相对减小;但在最高组分(x～3．1％)时,其寿命仍与NN4束缚激子的寿命相当(～30ns),说明GaP1-xNx混晶新形成的杂质带仍然保持束缚激子较长的辐射复合寿命。且该杂质带低能端载流子的寿命比高能端载流子的寿命长,导致了其时间分辨谱向低能端的移动。同时在低组分样品的时间分辨谱的测量中,直接观察到了从较浅NN对束缚激子向较深NN对束缚激子的能量传输现象。     

Magnetic field effect on transitions between direct and indirect excitons in diluted magnetic semiconductor double quantum wells

Transitions between direct and indirect excitons with change of magnetic field in double quantum well heterostructure Cd_1−xMg_xTe/Cd_1−yMg_yTe/Cd_1−xMg_xTe/Cd_1−zMn_zTe/Cd_1−xMg_xTe in external magnetic field are studied. The structure contains diluted magnetic semiconductor (Cd,Mn)Te layer that forms magnetic quantum well with the depth depending on the magnetic field intensity. Above some magnetic field the indirect exciton becomes the lowest excited state of the system. The indirect exciton lifetime exceeds by several orders of magnitude of the direct exciton one. The range of quantum well widths for which the indirect exciton is the exciton lowest state was estimated for the proposed system.     

Spin relaxation of Mn ions in (CdMn)Te/(CdMg)Te quantum wells under picosecond optical pumping

Spin relaxation of Mn ions in a Cd_0.97Mn_0.03Te/Cd_0.75Mg_0.25Te quantum well with photogenerated quasi-two-dimensional electron-hole plasma at liquid helium temperatures in an external magnetic field has been investigated. Heating of Mn ions by photogenerated carriers due to spin and energy exchange between the hot electron-hole plasma and Mn ions through direct sd-interaction between electron and Mn spins has been detected. This process has a short characteristic time of about 4 ns, which leads to appreciable heating of the Mn spin subsystem in about 0.5 ns. Even under uniform excitation of a dense electron-hole plasma, the Mn heating is spatially nonuniform, and leads to formation of spin domains in the quantum well magnetic subsystem. The relaxation time of spin domains after pulsed excitation is measured to be about 70 ns. Energy relaxation of excitons in the random exchange potential due to spin domains results from exciton diffusion in magnetic field B=14 T with a characteristic time of 1 to 4 ns. The relaxation time decreases with decreasing optical pump power, which indicates smaller dimensions of spin domains. In weak magnetic fields (_B=2 T) a slow down in the exciton diffusion to 15 ns has been detected. This slow down is due to exciton binding to neutral donors (formation of bound excitons) and smaller spin domain amplitudes in low magnetic fields. The optically determined spin-lattice relaxation time of Mn ions in a magnetic field of 14 T is 270±10 and 16±7 ns for Mn concentrations of 3% and 12%, respectively. Zh. éksp. Teor. Fiz. 112, 1440–1463 (October 1997)     

Magneto-optical study of the I4 bound exciton in ZnTe

The I₄ bound exciton at 2.315 eV in ZnTe is resolved into a quartet at fields from 40 – 148 kG. The field dependence of this quartet is qualitatively different from that of other exciton complexes in ZnTe. I₄ is assigned as due to ionized, substitutional Li acceptors at Zn sites.     

Exciton states in strongly coupled asymmetric semimagnetic double quantum dots

Exciton states in a pair of strongly coupled artificial asymmetric quantum dots (QDs) have been studied in magnetic fields up to B = 8T by means of photoluminescence spectroscopy. The QD molecules have been fabricated using a selective interdiffusion technique applied to asymmetric CdTe/(Cd,Mg,Mn)Te double quantum wells. The lateral confinement potential within the plane induced by the diffusion gives rise to effective zero-dimensional exciton localization. Incorporation of the Mn ions in only one dot results in a pair of QDs with a markedly different spin splitting. In contrast to a positive value of the exciton Lande g factor in nonmagnetic (Cd,Mg)Te-based single QDs, the ground exciton transition in the nonmagnetic QD demonstrates nearly zero g factor, thus, indicating a strong electron coupling between the dots. A new low-energy band with a strong red shift appears at high B signifying formation of the indirect exciton in accordance with our calculations. The text was submitted by the authors in English.     

Swelling Kinetics of PAAm–κ-Carrageenan Composites: A Fluorescence Technique

The steady-state fluorescence (SSF) technique was introduced for studying swelling of disc-shaped polyacrylamide (PAAm) gels containing various amount of κ?carrageenan (κC). They were prepared by free-radical cross-linking copolymerization. N,N^′-methylenebisacrylamide (BIS) and ammonium persulfate (APS) were added as a cross-linker and an initiator, respectively. Composite gels were prepared at 80°C with pyranine as a fluorescence probe. After drying of these gels, swelling kinetics were performed in water at 60°C by real-time monitoring of the pyranine fluorescence intensity, I, which decreased as swelling proceeded. The Li–Tanaka equation was used to determine the swelling time constants, τ ₁, and cooperative diffusion coefficients, D ₀, from fluorescence intensity, weight, and volume variations of the gels during the swelling processes in all cases. It was observed that τ ₁ decreased and D ₀ increased as the κC concentrations in the composites were increased indicating that high κC gels swell faster than low κC gels.     

Positron annihilation studies on molybdenum irradiated with neutrons at temperatures from 350° C to 1000° C

We performed measurements of positron lifetimes and the lineshape parameter on molybdenum samples irradiated with neutrons at temperatures from 350° to 1000° C. The results show that the correlation between swelling and positron characteristics depends strongly on irradiation temperature. From 350° to 500° C, ΔS, and notI ₂, correlates with sweelling; from 500° to 800° C, both ΔS andI ₂ correlate with swelling; and at higher temperatures, none of them correlates with swelling.     

超强磁场下非掺杂ZnSe/BeTe Ⅱ型量子阱中激子和带电激子的光学特性

报道了液态氦温度(4.2 K)下非掺杂ZnSe/BeTe Ⅱ型量子结构中ZnSe势阱层内空间直接光致发光(PL)光谱的磁场依赖性(磁场高达53 T).实验结果显示,随着磁场的增加,激子和带电激子的PL强度呈现出相反的振动行为.当激子的PL强度增加时带电激子的PL强度减小,反之,当激子的强度减小时带电激子的强度却增加.并且在整个磁场范围内,这些振动呈现近似等间隔的周期性变化.这个行为被解释为费米能级与朗道能级的周期性共振,这个共振导致了处于费米能级上的二维电子气态密度的周期性调制. 关键词： 光致发光 二维电子气 带电激子 Ⅱ型量子阱     

Study of the phase composition of AgI microcrystals by exciton spectroscopy and differential scanning calorimetry

Differential absorption spectra of RbAg₄I₅ have been measured in the exciton absorption region of AgI within the temperature range 27–250 °C. In the same temperature range, the temperature behavior of the heat capacity of RbAg₄I₅, Rb₂AgI₃, and KAg₄I₅ have been obtained by differential scanning calorimetry. An analysis of the results suggests that, in AgI microcrystals less than r _cr in size, the upper boundary for stability of the low-temperature β modification is higher by several tens of degrees. Fiz. Tverd. Tela (St. Petersburg) 40, 852–854 (May 1998)     

退火处理Fe43Co43Hf7B6Cu1非晶合金的正电子湮没研究

对熔体急冷法制备的Fe₄₃Co₄₃Hf₇B₆Cu₁非晶合金进行了200,300,400和500 ℃保温30 min的退火处理,用正电子湮没寿命谱、X射线衍射、穆斯堡尔谱等方法研究了退火后试样的结构及结构缺陷变化.结果表明,在非晶合金的制备态,正电子主要在非晶基体相空位尺寸的自由体积中湮没,湮没寿命τ₁为158.4 ps,强度I₁关键词： 43Co₄₃Hf₇B₆Cu₁非晶')" href="#">Fe₄₃Co₄₃Hf₇B₆Cu₁非晶 退火处理 正电子湮没寿命 结构与结构缺陷     

Thermodynamical behavior of E′ centers in quartz from sediments: Potential for paleothermometry and geochronometry

The thermodynamical behaviors of E′ centers in 8 quartz samples from core XJ33-2-1 recovered in the Zhujiang Mouth Basin were measured by electron spin resonance (ESR) technique. The E′ ESR spectral intensity of samples before any laboratory treatment was measured and expressed asI ₁. The samples were then annealed at 300°C or 350°C for 60 min. The E′ ESR spectral intensity measured after this procedure is expressed asI ₂. The ratios ofI ₁, toI ₂ for the samples increase with the sample depth (from 320 to 3972 m), showing that there is a correlation between this ratio and the storage temperature of samples. Therefore the ratio ofI ₁/I ₂ can be used as an ESR paleothermometer. Besides the temperature, we must take into account the period of time for which the samples have been buried since their deposition, because we find that the ratiosI ₁/I ₂ (from 0.293 to 0.941) are closely related to the sediment ages (from 1.5 to 27.5 Ma), with a correlation coefficient of 0.98 or 0.99 obtained by linear or exponential regression, respectively. This relation can be explained by the increase of E′ center concentration in quartz samples with the sedimentation age.