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.     

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     

双波长自由载流子吸收技术测量半导体载流子体寿命和表面复合速率

提出了采用双波长自由载流子吸收技术同时测量半导体材料载流子体寿命和前表面复合速率的方法.通过数值模拟,定性分析了不同载流子体寿命和前表面复合速率对信号的影响,同时对测量参数的可接受范围和不确定度进行计算并与传统频率扫描自由载流子吸收方法测量结果进行比较.结果表明：提出的双波长自由载流子吸收方法可明显减小载流子体寿命和前表面复合速率的测量不确定度,提高参数测量精度;表面杂质和缺陷越多的样品,其前表面复合速率测量不确定度越小.进一步分析表明,此现象与不同波长激光抽运产生的过剩载流子浓度分布不同有关.     

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.     

硅太阳能电池的调制载流子红外辐射动态响应与参数分析

建立了调制激光诱发硅太阳能电池的少数载流子密度波数学模型,并利用光致载流子辐射检测掺杂浓度、阻抗及载流子输运参数. 对频域响应曲线中的双弯曲效应进行了研究,构建了小交流信号作用的太阳能电池等效电路拓扑结构,仿真分析了不同掺杂浓度、阻抗电阻和载流子传输参数对频响曲线拐点的影响. 通过光致载流子辐射频域扫描实验与多参数拟合检测了单晶硅太阳电池的施/受主浓度、并联电阻和载流子输运参数. 结果表明：光致载流子辐射技术检测大面积太阳能电池频响曲线的双弯曲是由电容效应所引起的,建立的数学模型可定量描述和预测检测结果,并用于测量太阳能电池的掺杂浓度、电阻和载流子输运参数. 关键词： 调制自由载流子辐射 扫频检测 PN结电容 参数测量     

双光子激发ZnSe自由载流子超快动力学研究

采用Z扫描和抽运-探测实验技术, 在波长为532 nm、脉冲宽度为41 fs的条件下测得ZnSe晶体的双光子吸收系数, 并获得了不同激发光强下的自由载流子吸收截面、电子-空穴带间复合时间和电子-声子耦合时间. 研究发现, 随着激发光强的增大, 自由载流子吸收截面减小, 复合时间变短. 当激发光强增大导致载流子浓度大于10¹⁸ cm^-3时, 抽运-探测信号出现明显改变, 原因归结为强光场激发导致样品在短时间内带隙变窄和电子-空穴等离子体的形成.     

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.     

GaAs在光通讯波段的超快非线性光学研究

采用Z-扫描和泵浦-探测技术,在光通讯波段对砷化镓(GaAs)单晶进行了非线性动力学以及非线性光学的实验研究.飞秒泵浦-探测实验结果表明,三阶非线性光学效应源于砷化镓单晶对飞秒激光的瞬态双光子吸收,而五阶非线性光学效应源于砷化镓单晶双光子吸收诱导的自由载流子吸收效应.通过Z扫描实验,得到了关于GaAs单晶所有的非线性光学参数,包括双光子吸收系数、三阶非线性折射系数、双光子吸收诱导的自由载流子吸收截面以及双光子吸收诱导的自由载流子折射截面.结果表明,砷化镓单晶在制造光限幅器件和光电探测器方面具有良好的发展前景.     

抽运-探测反射技术研究本征CdTe的载流子动力学

采用抽运-探测反射技术,研究了室温下本征CdTe晶体的光致非平衡载流子布局与光子能量和抽运光强的关系.根据实验结果,发现随着抽运光光子能量的提高,快过程在载流子弛豫过程中所占的比例增大;随着抽运光功率的提高,反射率随之增大,快过程时间常数也随之增大.通过建立简单的本征半导体受激载流子弛豫过程模型,讨论了载流子散射、载流子-声子相互作用和载流子复合等的贡献.在抽运光光子能量为1.49 eV(比CdTe的禁带宽度约高20 meV)时,通过双指数函数拟合,得到了本征CdTe中载流子弛豫过程的快、慢时间常数,分别为2.8 ps和158.3 ps.     

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。     

Analysis of free carrier absorption measurement of electronic transport properties of silicon wafers

Sensitivity analysis of electronic transport property measurement of silicon wafers with modulated free carrier absorption (MFCA) technique and multi-parameter fitting procedure is performed. The sensitivity of the multi-parameter estimate employing the dependences of the MFCA amplitude and phase on the pump-probe-beam separation measured at several modulation frequencies covering an appropriate range is theoretically compared with that employing only the dependences of the MFCA amplitude and phase on the modulation frequency. Simulation results show that the dependences of the MFCA amplitude and phase on the pump-probe beam separation are more sensitive to the electronic transport properties of silicon wafers than the frequency dependences. The electronic transport properties of the silicon wafers determined with the two-beam separation dependence are therefore more accurate than that determined with the frequency dependence. Comparative experiments with a silicon wafer are performed and the carrier lifetime, the carrier diffusivity, and the front surface recombination velocity are determined simultaneously and unambiguously with both techniques.     

Measurement accuracy analysis of the free carrier absorption determination of the electronic transport properties of silicon wafers

By introducing the random and systematic errors in simulated data computed from conventional frequency-scan and laterally resolved modulated free carrier absorption theory models, we investigate the relative determination sensitivities of three electronic transport properties, namely, carrier lifetime, carrier diffusivity and front surface recombination velocity of silicon wafers determined by frequency-scan and laterally resolved techniques. The phase and amplitude data with random errors as functions of the modulation frequency at zero pump-probe-beam separation or of the two-beam separation at four different modulation frequencies are simultaneously fitted to an appreciated carrier diffusion model to extract three transport parameters. The statistical results and fitted accuracies of the transport parameter determined by both techniques are theoretically analysed. Corresponding experimental results are carried out to compare to the simulated results. The simulated and experimental results show that the determination of the transport properties of silicon wafers by the laterally resolved technique are more accurate, as compared with that by the frequency-scan technique.     

Time-domain modulated free-carrier absorption measurements of recombination process in silicon wafers

A time-domain modulated free-carrier absorption (MFCA) is developed both experimentally and theoretically to investigate the photo-carrier dynamics of silicon wafers illuminated by a square-wave-modulated super-band-gap laser beam. An explicit three-dimensional (3-D) theoretical expression for the temporal behavior of the MFCA signal is obtained by solving a 3-D carrier-diffusion equation The time-domain MFCA model is used to fit the experimental MFCA signals of p- and n-type Si wafers via a multi-parameter fitting procedure to determine simultaneously the electronic transport properties, that is, the bulk lifetime, the ambipolor diffusivity, and the front surface recombination velocity. The uncertainties of the fitted parameter values are estimated.     

Photothermal deflection investigation of bulk Si and GaSb transport properties

The photo-thermal deflection technique (PTD) is used to study the transport properties such as non-radiative lifetime of minority carriers (τ _nr), electronic diffusivity (D) and surface recombination velocity (S) in bulk silicon (Si) and gallium antimonide (GaSb) semiconductors. A generalized one-dimensional theoretical model has been also developed, and the coincidence between experimental curves giving the normalized amplitude and phase variations versus square root modulation frequency and the corresponding theoretical curves makes possible to deduce the electronic parameters cited above.     

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.     

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%.