方波调制下自由载流子吸收测量半导体载流子输运参数的时域模型

本文建立了用于测量半导体载流子输运特性(载流子寿命、载流子扩散系数和前表面复合速度)的方波调制下自由载流子吸收(free carrier absorption,FCA)检测技术的时域理论模型.通过数值模拟,分析了在不同调制频率下时域曲线的变化趋势以及各个载流子输运参数对时域曲线的影响.结果表明方波调制下的自由载流子吸收的时域信号对各个参数都用较高的灵敏度,且参数值的测量范围大于频域测量范围.     

调制激光致硅晶圆载流子辐射扫描成像试验研究

建立了调制激光诱发硅晶圆少数载流子密度波一维模型, 仿真分析了少数载流子输运参数对调制激光诱发载流子辐射信号频域响应的影响. 利用调制激光诱发载流子辐射扫描成像系统对含有表面划痕的硅晶圆进行了扫描成像试验研究. 通过少数载流子密度波模型与多参数拟合方法反求得到了扫描区域的输运参数二维分布图. 该方法得到的少数载流子寿命与利用传统光电导方法测量的少数载流子寿命结果相符; 分析了划痕对载流子输运参数造成的影响, 与光电导方法比较, 该方法可以测量不同位置的全部载流子输运参数且分辨率高.     

光子重吸收对硅片的光载流子辐射特性影响的理论研究

光载流子辐射技术已广泛应用于半导体材料性能的表征,本文基于一种包含光子重吸收效应的光载流子辐射理论模型,对单晶硅中光子重吸收效应对光载流子辐射信号的影响进行了详细的理论分析.分析结果表明,光子重吸收效应对光载流子辐射信号的影响主要取决于样品掺杂浓度、过剩载流子浓度和过剩载流子的分布.由于过剩载流子浓度及其分布与材料电子输运特性密切相关,电子输运参数的变化将导致光子重吸收效应的影响随之变化.进一步分析了光子重吸收效应对具有不同电子输运特性的样品的电子输运参数的影响,并提出了减小光子重吸收效应影响的方法.     

调制自由载流子吸收测量半导体载流子输运参数的三维理论

推导出用于测量半导体载流子输运特性(载流子寿命、载流子扩散系数和前表面复合速度)的调制自由载流子吸收(modulated free carrier absorption, MFCA)检测技术的三维理论模型,给出了调制自由载流子吸收检测信号与调制频率和抽运-探测光相对距离的关系.定性分析了在不同调制频率时各个载流子输运参数对径向位置扫描曲线(信号与两束光相对距离的关系)的影响,结果表明调制自由载流子吸收检测信号对各个参数的灵敏度随抽运-探测光相对距离的增加而增加.仿真和实验结果表明,通过拟合不同调制频率时调 关键词： 调制自由载流子吸收 载流子输运特性 径向位置扫描     

锁相载流子成像技术在太阳能电池中的应用

提出了一种基于锁相载流子成像技术的太阳能电池特性研究方法。激光激励的红外光生载流子辐射测量技术是一种动态的近红外调制的光致发光成像技术,已经被证实为半导体输运参数的一种行之有效的非接触测量方法。提出的锁相载流子成像技术则是一种基于红外相机的动态近红外光生载流子辐射光致发光法,它是光生载流子技术在成像领域的延伸。采用锁相载流子成像系统对10片样片进行了实验,并对获得的红外图像进行了统计分析,由此得到了载流子成像统计参数与太阳能电池光电转换效率间的相关特性。结果表明,锁相载流子成像的统计参数可用于表征太阳能电池的效率。     

半导体特性的调制自由载流子吸收变距频率扫描方法研究

根据调制自由载流子吸收（modulated free carrier absorption,MFCA）检测技术的三维理论模型,采用变间距频率扫描方式测量单晶硅样品的电子输运参数,进行了仿真与实验,对结果进行了分析;通过多参数拟合,获取了测试样品的载流子扩散系数、少数载流子寿命和前表面复合速度.仿真与实验都表明,变间距频率扫描结合多参数拟合,可以提高输运参数的测量精度. 关键词： 调制自由载流子吸收 电子输运参数 变间距频率扫描 多参数拟合     

N型稀磁半导体Ge_(0.96–x) Bi_xFe_(0.04)Te薄膜的磁电性质研究

GeTe基稀磁半导体材料因具有可独立调控载流子浓度和磁性离子浓度的特性而受到广泛关注.本文利用脉冲激光沉积技术制备了该体系的单晶外延薄膜,并通过高价态Bi元素部分取代Ge元素的方法实现了材料中载流子类型从空穴向电子的转变,即制备出N型GeTe基稀磁半导体.测量结果表明,无论是室温还是低温下的Hall电阻曲线皆呈现负斜率,说明体系中载流子是电子;并且当Bi掺杂量达到32%时,电子浓度为10~(21)/cm~3.变温输运性质的测量证明体系的输运行为呈现半导体特征.通过测量低温10 K下的绝热磁化曲线,在高Bi掺杂体系中观测到了明显的铁磁行为,而低于32%Bi掺杂量的体系中未观察到.这一结果说明,高掺杂Bi的替代导致载流子浓度的增加,促进了载流子传递Ruderman-Kittel-Kasuya-Yoshida相互作用,使得分散的Fe-Fe之间产生磁耦合作用,进而形成铁磁有序态.     

不同背场的GaAs基单结太阳能电池伏安特性及分析

介绍了GaAs基太阳能电池的原理、等效电路及性能参数,基于集成电路工艺与器件计算机辅助工艺设计(TCAD)仿真工具,设计了背场分别为InAlGaP和InAlP的两种GaAs基太阳能电池,并对其结构和性能进行仿真。同时,通过分子束外延(MBE)设备制备了这两种太阳能电池,并测试了其伏安(IV)特性。在考虑并联电阻和串联电阻对太阳能电池伏安特性的实际影响后,仿真结果与实验结果基本一致。重掺杂(原子浓度为2×1018 cm-3)的InAlGaP作为GaAs太阳能电池背场时,伏安特性曲线是典型的太阳能电池的伏安特性。重掺杂(原子浓度为2×1018 cm-3)的InAlP作为GaAs太阳能电池背场时,伏安特性曲线呈现"S"形变化。分析结果表明,背场与基层形成漂移场,加速了光生少子在电池中的输运,提高了光生电流,同时,背场将光生少子反射回有源区,降低了背表面的复合概率。当InAlP作为背场时,由于异质结的存在,影响了载流子的运输,在较小的偏压下,载流子主要通过隧道效应越过势垒,在较大的偏压下,载流子主要通过热电子发射越过势垒,因此伏安特性曲线呈现"S"形变化。     

紫外光辐照对TiO2纳米线电输运性能的影响及磁阻效应研究

采用溶胶凝胶法以及静电纺丝法, 利用热处理工艺, 成功制备出了多晶锐钛矿型TiO₂纳米线, 通过两线法在室温下测试单根TiO₂纳米线的V-I曲线来研究其电输运性能及磁阻效应. 结果表明: 在无光照环境下其V-I曲线为不过零点的直线, 零场电阻较大, 在磁场作用下电阻下降, 表现出负磁阻效应; 紫外光辐照环境下TiO₂纳米线载流子浓度增加使得电阻变小, 然而在磁场作用下电阻增大, 表现为正磁阻效应. 紫外光辐照导致的载流子浓度变化, 使得负磁阻转变为正磁阻, 我们将磁阻变化归结为d电子局域导致的负磁阻与能带劈裂导致的正磁阻两种机理相互竞争的结果.     

无注入型发光二极管的载流子输运模型研究

无载流子注入型发光二极管(简称无注入型LED)因其简单的器件结构有望应用于Micro-LED、纳米像元发光显示等新型微显示技术.由于没有外部载流子注入,无注入型LED的内部载流子输运行为无法直接用传统的PN结理论进行描述.因此,建立无注入型LED的载流子输运模型对于理解其工作机理和提高器件性能具有重要意义.本文根据无注入型LED的器件结构,结合PN结理论建立无注入型LED的载流子输运数学模型.基于该数学模型解释器件的工作原理,获得器件的载流子输运特性,揭示感应电荷区长度、内部PN结压降与外加驱动电压频率的关系.根据建立的数学模型提出了针对无注入型LED器件设计的建议:1)减小感应电荷区掺杂浓度,可有效提高内部LED的压降;2)利用PN结的隧穿效应,可有效提高器件内部LED的压降;3)使用正负方波驱动可以获得比正弦驱动更大的内部LED压降.本文有关无注入型LED的载流子输运模型的研究有望为改善无注入型LED器件结构、优化工作模式提供理论指导.     

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.     

Effect of incidence angle on the electrical parameters of vertical parallel junction silicon solar cell under frequency domain

The effect of incidence angle on the electrical parameters of vertical parallel silicon solar cell under frequency domain was theoretically analyzed. Based on the diffusion-recombination equation, the expression of excess minority carrier density in the base was established according to the modulation frequency and the illumination incidence angle. The excess minority carrier density, the photocurrent density, the photo voltage, series resistance, shunt resistance, electric power and the space charge region capacitance were calculated and plotted. The objective of this work was to show the effects of solar cell modulation frequency and the illumination incidence angle on these electrical parameters, electric power and space charge region capacitance. Plots of solar cell’s electric power with the junction recombination velocity gave the maximum solar cell’s electric power; Pm. Influence of various parameters of incidence angles on the solar cell’s electric power was also studied.     

Differential nonlinear photocarrier radiometry for characterizing ultra-low energy boron implantation in silicon

The measuring of the depth profile and electrical activity of implantation impurity in the top nanometer range of silicon encounters various difficulties and limitations, though it is known to be critical in fabrication of silicon complementary metal-oxide-semiconductor (CMOS) devices. In the present work, SRIM program and photocarrier radiometry (PCR) are employed to monitor the boron implantation in industrial-grade silicon in an ultra-low implantation energy range from 0.5 keV to 5 keV. The differential PCR technique, which is improved by greatly shortening the measurement time through the simplification of reference sample, is used to investigate the effects of implantation energy on the frequency behavior of the PCR signal for ultra-shallow junction. The transport parameters and thickness of shallow junction, extracted via multi-parameter fitting the dependence of differential PCR signal on modulation frequency to the corresponding theoretical model, well explain the energy dependence of PCR signal and further quantitatively characterize the recovery degree of structure damage induced by ion implantation and the electrical activation degree of impurities. The monitoring of nm-level thickness and electronic properties exhibits high sensitivity and apparent monotonicity over the industrially relevant implantation energy range. The depth profiles of implantation boron in silicon with the typical electrical damage threshold (Y_ED) of 5.3×10¹⁵ cm^-3 are evaluated by the SRIM program, and the determined thickness values are consistent well with those extracted by the differential PCR. It is demonstrated that the SRIM and the PCR are both effective tools to characterize ultra-low energy ion implantation in silicon.     

选择性发射极晶体硅太阳电池的二维器件模拟及性能优化

利用PC2D二维模拟软件对选择性发射极晶体硅太阳电池(SE电池)进行了器件模拟和参数优化的研究.在对丝网印刷磷浆法制备的SE电池的实测典型电流-电压曲线实现完美拟合的基础上,全面系统地研究了栅线、基区、选择性发射区和背表面场层等的参数对电池性能的影响.模拟表明:基区少子寿命、前表面复合速度和背表面复合速度是对电池效率影响幅度最大的三个参数.在所研究的参数范围内,当基区少子寿命从50μs上升到600μs时,电池效率从18.53%上升到19.27%.低的前表面复合速度是使发射区方块电阻配比优化有意义的前提.要取得理想的电池效率,背表面复合速度需控制在500 cm/s以下.此外,对于不同的前表面复合速度,电池效率的最大值总是在50—90Ω/□的重掺区方阻、110—180Ω/□的轻掺区方阻的范围内取得.对不同的栅线数目,重掺区宽度与栅线间距之比为32%时,电池的效率最高.另外,在主栅结构保持较低面积比率的前提下,主栅数目的增加也可提高效率.最后,通过优化p型SE电池的效率可达到20.45%.     

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.     

低温退火磷吸杂工艺对低少子寿命铸造多晶硅电性能的影响

本文针对低少子寿命铸造多晶硅片进行试验, 通过一种将多温度梯度磷扩散吸杂工艺与低温退火工艺结合的新型低温退火吸杂工艺, 去除低少子寿命多晶硅片中影响其电性能的Fe杂质及部分晶体缺陷, 提高低少子寿命多晶硅所生产的太阳电池各项电性能. 通过低温退火磷扩散吸杂工艺与其他磷扩散吸杂工艺的比较, 证明了低温退火吸杂工艺具有更好的磷吸杂和修复晶体缺陷的作用. IV-measurement发现经过低温退火工艺处理后的低少子寿命多晶硅, 制备的太阳电池光电转换效率比其他实验组高0.2%, 表明该工艺能有效地提高低少子寿命多晶硅太阳电池各项电性能参数及电池质量. 本研究结果表明新型低温退火磷吸杂工艺可将低少子寿命硅片应用于大规模太阳电池生产中, 提高铸造多晶硅材料在太阳能领域的利用率, 节约铸造多晶硅的生产成本. 关键词： 低温退火 磷吸杂 低少子寿命多晶硅 太阳电池     

Photoelectronic characterization of n-type silicon wafers using photocarrier radiometry

Photocarrier radiometry (PCR) was used to characterize four n-type silicon wafers with different resistivity values in the 1-20 Ω cm range. Simulations of the PCR signal have been performed to study the influence of the recombination lifetime and front surface recombination velocity on them; besides, the transport parameters (carrier recombination lifetime, diffusion coefficient, and frontal surface recombination) of the wafers were obtained by means of a fitting procedure. The PCR images that are related to the lifetime are presented, and the first photoelectronic images of a porous silicon sample are obtained.