光折变聚合物中载流子特性对空间电荷场的影响

根据适用于光折变聚合物系统的空间电荷场形成的动力学微分方程,将陷阱情况分为四类,分别讨论了光折变聚合物中光生载流子的量子产生效率及其迁移率对空间电荷场的稳态和动态特性的影响.结果发现空间电荷场的稳态特性相对于光生载流子的量子产生效率的变化比较敏感,而空间电荷场的动态特性则易受到载流子的迁移变化的影响.     

短脉冲光在光伏光折变晶体中写入和擦除光折变光栅理论研究

利用GC Valley的准连续光(Quasi-cw)近似模型,研究了短脉冲激光(纳秒ns量级)在光伏光折变材料LiNbO3晶体中写入和擦除光折变光栅的过程,给出了空间电荷场随时间变化的表达式.理论研究表明,空间电荷场的形成和擦除与两个时间参量有关,在考虑或者不考虑光生伏打效应两种情况下,这两个参量随擦除光强的变化有基本相同的变化规律,光栅的写入和擦除有相同的结果.同样,擦除一个光栅所需的光能量在两种情况下也有相同的结果.因此,在短脉冲光入射光折变晶体材料情况下,考虑光生伏打效应与不考虑光伏效应,对短脉冲光在光折变LiNbO3晶体中写入和擦除光栅基本没有影响.     

Ce:KNSBN晶体中双光束耦合的研究

本文对光折变晶体的衍射效率进行了理论性的分析研究,并以晶体Ce:KNSBN(含锗的钾钠锐酸锶钡)为对象进行了实验上的探索.证实其光生载流子的迁移机制在空间电荷场形成过程中以扩散为主.     

光生伏打-光折变介质中光学涡旋孤子

简化了描述光生伏打光折变效应的模型方程.给出了光生伏打空间电荷场的形式解.讨论了单光束在光生伏打、自散焦光折变介质(LiNbO3∶Fe晶体)中的三维传播行为.指出在适当近似条件下,光生伏打光折变非线性可以维持圆对称的涡旋孤子. 关键词：     

光电导过程中陷阱的影响

从理论上提出光折变材料中光电导过程的陷阱作用机制，给出了载流子的光激发，复合及俘获过程的动力学方程，得到了陷阱作用下的光生量子效率的解析表达式，实验上，对掺杂不同浓度的Ｃ６０（Ｃ７０）的ＰＶＫ薄膜的光生载流子量子效率随光强度的变化关系进行了测量，得到了与理论预测相一致的结果。     

掺杂无机纳米超微粒的有机聚合物体系中的光折变效应

研究了掺杂无机纳米超微粒的有机聚合物体系中的光折变效应．体系中以Ｃｕ２Ｓ／ＣｄＳ／ＺｎＳ复合超微粒为光敏剂,ＰＶＫ为载流子输运剂,电光分子为ＥＰＮＡＣ．给出了光敏剂的制备方法,ＥＰＮＡＣ的分子结构及电光特性,以及该光折变材料中的两波耦合效应的实验结果．结果表明,无机纳米超微粒可用作光折变材料中的光敏剂,这是它的一种新的应用．     

大调制度下光折变运动光栅的微扰分析

利用“跳跃模型”讨论了大调制度下光折变材料对运动干涉条纹的非静态记录过程，给出了描述运动干涉条纹非静态记录时电荷密度波前三阶分量振幅的微分方程，以及前三阶空间电荷场的解析表达式.讨论了前三阶空间电荷场振幅改变量对干涉条纹运动速度的依赖关系，若扩散场不为零但较小时，施加较小的外电场能够实现对空间电荷场高阶分量选择性地增强.若扩散场较大(大于外加电场)，则不能实现对空间电荷场高阶分量选择性地增强. 关键词：     

KTa_(1-x)Nb_xO_3:Cu晶体中直流空间电荷场的进一步研究

分别用扩束光和一束写入光对KTa_(1-x)Nb_xO_3:Cu(X=0.32)晶体中的光折变栅进行擦洗,通过不同的擦洗效果,进一步论证了在写入过程中除了形成周期分布的空间电荷场之外,同时还形成了直流空间电荷场.并对直流空间电荷场被擦洗的动态过程进行了详细研究.此外,在写入之前利用一束均匀光照射在外加电场作用下的KTa_(1-x)Nb_xO_3:Cu晶体,研究了直流空间电荷场的形成对衍射信号强度的影响.     

有机层界面对双层有机发光二极管复合效率的影响

建立了双层有机发光二极管中载流子在有机层界面复合的无序跳跃理论模型.由于有机分子材料的空间及能带结构的无序性，采用刚体模型处理有机层界面问题是不恰当的，而采用无序跳跃模型比较合理.复合效率及复合电流由载流子跳跃距离、有机层界面的有效势垒高度及该界面处的电场强度分布所决定：在双层器件ITO/α-NPD/Alq₃/Al中，当所加电压小于19.5V时，复合效率随着载流子跳跃距离的增加而增加，而大于19.5V时，复合效率随着其距离的增加而减少；复合效率随着有机层界面有效势垒高度的增加而增加； 关键词： 有机层界面 双层有机发光二极管 复合效率 有效势垒高度 无序跳跃模型     

强外加电场与大调制度下光折变动力学光栅形成研究

强外加电场与大调制度在光折变效应的研究中已经得到了广泛应用。采用PDECOL算法,严格求解光折变带输运方程,得到外加电场时不同调制度下光折变晶体中随时间变化的空间电荷场、载流子浓度,并讨论了外加电场对它们的影响。通过将物质方程与耦合波方程联立数值求解,可得到光折变光栅形成过程中两波耦合增益系数以及光束条纹相位的变化。模拟结果表明,在强外加电场作用下,两束记录光之间的光强与相位耦合都得到了增强,而原有的解析式忽视了强外加电场与大调制度对空间电荷场相位耦合的影响,此时不再适用。同时发现折射率光栅与记录光束条纹均发生弯曲,并不再保持平行。     

光折变晶体η-2θ曲线峰值位置明显偏移的研究

实验发现在Ce:(K_0.5Na_0.5)_0.2(Sr_0.61Ba_0.39)_0.9Nb₂O₆(Ce:KNSBN)光折变晶体的同一点记录两幅光栅时,其中一幅光栅的衍射效率(η)相对于两光束夹角(2θ)的关系曲线峰值位置由仅存储一幅光栅时的36°变为44°.采用跳跃模型的微扰分析方法解释了这一现象.     

界面空间电荷对双层有机电致发光器件效率的影响

本文建立了双层有机电致发光器件中载流子在有机/有机界面复合的无序跳跃理论模型.计算表明:①内界面处电子和空穴的有效势垒高义决定OLEDs中的电子和空穴密度的分布,而电子与空穴密度又决定了电场强度的大小;且复合效率随着有效势垒高度的增加而增加;②当电压较低时,复合效率随载流子有效跳跃距离的增加而增加;当电压较高时,复合效率随载流子的有效跳跃距离的增加而减少;③当界面场强差较小时,有机层界面场强突变增大,复合效率增大,当界面场强差达临界值时,复合效率反而随着界面场强差的增大而减小.该理论模型可较好地解释相关的实验现象.     

Thermal annealing induced photocarrier radiometry enhancement for ion implanted silicon wafers

An experimental study on the photocarrier radiometry signals of As⁺ ion implanted silicon wafers before and after rapid thermal annealing is performed. The dependences of photocarrier radiometry amplitude on ion implantation dose (1×10¹¹--1×10¹⁶/cm²), implantation energy (20--140 keV) and subsequent isochronical annealing temperature (500--1100 du are investigated. The results show that photocarrier radiometry signals are greatly enhanced for implanted samples annealed at high temperature, especially for those with a high implantation dose. The reduced surface recombination rate resulting from a high built-in electric field generated by annealing-activated impurities in the pn junction is believed to be responsible for the photocarrier radiometry signal enhancement. Photocarrier radiometry is contactless and can therefore be used as an effective in-line tool for the thermal annealing process monitoring of the ion-implanted wafers in semiconductor industries.     

Effect of electric field on diffusion in disordered materials

The effect of electric field on diffusion of charge carriers in disordered materials is studied by Monte Carlo computer simulations and analytical calculations. It is shown how an electric field enhances the diffusion coefficient in the hopping transport mode. The enhancement essentially depends on the temperature and on the energy scale of the disorder potential. It is shown that in one‐dimensional hopping the diffusion coefficient depends linearly on the electric field, while for hopping in three dimensions the dependence is quadratic.     

Limit Properties of One Dimensional Periodic Hopping Model

在细致平衡的基础上,通过形式运算得到了平均速度及有效扩散常数在模型的内部状态数量趋向无穷大时的极限显示表达式．这一结果将有助于进一步了解一维跳跃模型的性质.     

Congruent Sr 0.61 Ba 0.39 Nb 2 O 6 doubly doped with Ce and Cr: PHoto- and thermoluminescence investigations

Congruent Sr x Ba 1 m x Nb 2 O 6 (SBN, x=0.61) doped with Ce or Cr ions exhibits enhanced photorefractive properties and new spectral features like increased red sensitivity. Here special emphasis is placed on the luminescence features of doubly doped Ce+Cr SBN crystals. The luminescence excitation and emission spectra combined with the absorption of the impurities allow to draw conclusions about the origin of the charge carriers und their recombination. The well separated thermo-luminescence peaks detected and their spectral line shape in emission point to specific recombination processes following the thermal liberation of light-induced electron trapping centers: Nb 4+ polarons and VIS-centers created at low temperature under light irradiation. The thermal activation energy for the hopping motion of Nb 4+ polarons and of VIS-centers are estimated to be 0.18 - 0.02 v eV and 0.30 - 0.05 v eV respectively. Possible excitation and recombination mechanisms in SBN:Ce+Cr are discussed.     

Photocarrier radiometry for noncontact evaluation of space monocrystalline silicon solar cell under low-energy electron irradiation

A space monocrystalline silicon(c-Si) solar cell under low-energy( 1 MeV) electron irradiation was investigated using noncontact photocarrier radiometry(PCR). Monte Carlo simulation(MCS) was employed to characterize the effect of different energy electron irradiation on the c-Si solar cell. The carrier transport parameters(carrier lifetime, diffusion coefficient, and surface recombination velocities) were obtained by best fitting the experimental results with a theoretical one-dimensional two-layer PCR model. The results showed that the increase of the irradiation electron energy caused a large reduction of the carrier lifetime and diffusion length. Furthermore, the rear surface recombination velocity of the Si:p base of the solar cell at the irradiation electron energy of 1 Me V was dramatically enhanced due to 1 MeV electron passing through the whole cell. Short-circuit current(I sc) degradation evaluated by PCR was in good agreement with that obtained by electrical measurement.     

Self-enhanced diffraction properties of a nominally undoped barium titanate crystal with a thermally fixed grating

We describe recent studies on diffraction properties of a photorefractive barium titanate crystal having a thermally fixed grating. Buildup dynamics of diffracted signals are measured to analyze the contributions of ionic and re-created photocarrier (hole) gratings to the temperature-dependent diffraction efficiency in self-enhanced readout. An activation energy of mobile ions as nonphotoactive secondary carriers for fixing volume holograms is determined holographically. This value is compared with that of hydrogen ions estimated from polarization-dependent infrared absorption spectra in order to indentify the fixing species.