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     

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     

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     

Ge掺杂GaN晶体双光子诱导超快载流子动力学的飞秒瞬态吸收光谱研究

本文利用飞秒瞬态吸收光谱技术,在近红外波段对Ge掺杂GaN(GaN:Ge)晶体进行了超快载流子动力学研究.在双光子激发下,瞬态吸收动力学呈现出双指数衰减,其中慢过程寿命随着泵浦光强增加而增加.瞬态吸收响应随着探测波长而单调增强,并在约1050nm处由空穴吸收占据主导.利用简化模型模拟载流子动力学发现,GaN:Ge中碳杂质形成的深受主能级对空穴有很强的俘获能力,并且引起了缺陷发光.在较适中的载流子注入下,n型GaN中的载流子寿命可以通过控制缺陷浓度和载流子浓度来共同调控,使其可应用于发光二极管和光通信等不同的领域.     

GaN基多量子阱发光二极管的极化效应和载流子不均匀分布及其影响

制备了GaN基绿光发光二极管.利用耦合法求解了在自发极化和压电极化效应影响下的GaN/InGaN量子阱的极化电场强度.考虑载流子在量子阱间的不均匀分布，模拟计算了系统的一维薛定谔方程、稳态速率方程和泊松方程，得到了载流子在各个阱间的分布比值和辐射复合速率.同时还得到了不同电流下电致发光(EL)谱的峰值波长、谱峰半高宽及EL谱强度的变化情况.发现当测试电流由10 mA 增加到70 mA时，理论结果与实验结果能很好符合. 关键词： 极化 载流子不均匀分布 复合速率     

一种测量p-GaN载流子浓度的方法

提出了一种测量p-GaN载流子浓度的方法,其主要思想是利用p-n⁺结构GaN探测器长波和短波量子效率的差值随反向偏压的变化关系,找到p-GaN层刚好完全耗尽时的偏压,从而求出p-GaN层载流子浓度.模拟计算表明,该方法能够准确测量出p-GaN层的载流子浓度,而且受表面复合、欧姆接触影响很小.进一步研究了实际测量中如何选择p-GaN层厚度,计算结果表明,p-GaN层的优化厚度值随着p-GaN层的浓度增加而减小. 关键词： p-GaN 载流子浓度测量 紫外探测器     

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.     

绝缘衬底上硅表面载流子的超快动力学研究

利用800 nm波长的飞秒抽运探测技术测量r具有不同单晶硅薄膜厚度的绝缘衬底上硅(SOI)皮秒瞬态反射率变化,并通过基于受激载流子密度和温度变化过程建立的反射率模型讨论了SOI表面载流子的超快动力学过程.研究表明,表面复合速度(SRV)是影响载流子动力学响应的主要因素,且薄膜厚度越小表面复合速度就越大,对应的表面态密度可达到1013cm-2 .对于较小的SRV,受激载流子的超快响应决定了瞬念反射率变化;而对于较大的SRV,晶格温升对瞬态反射率变化的贞献变得显著,使得反射率在更短的时间内恢复并超过初始值.     

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-resolved spectroscopy for 5s~('4)D_(7/2) state transitions undergoing electron–ion recombination in femtosecond laser-produced copper plasma

In the femtosecond laser-produced Cu-plasma, the transient transition dynamics that the excited state 5s~('4)D_(7/2) via electron–ion recombination transfers to 4p~('4)F_(9/2)~0(465.11 nm, Λ1 line) and 4p~('4)D_(7/2)~0(529.25 nm, Λ_2 line) states are investigated by using the time-resolved spectroscopy. The occupation number and relevant lifetime of the excited state 5s~('4)D_(7/2),the temporal evolutions of spectral intensities for Λ_1 line and Λ_2 line emissions are demonstrated to be in direct proportion to the employed laser intensity, which reveals the transient features of transition dynamics clearly differing from that resulted in the traditional collision excitation. Furthermore, some unique characteristics for Λ_1 and Λ_2 transitions stemming from electron–ion recombination are examined in detail.     

Time‐resolved free carrier lifetime microscopy in bulk GaN

A novel setup for lifetime microscopy measurements was designed and applied for carrier lifetime mapping in a bulk GaN. Photoexcitation by a picosecond UV pump and detection of time‐resolved free carrier absorption (FCA) images on a CCD camera enabled the mapping of carrier lifetime distribution with a spatial resolution of 5 μm. The spatial variation of lifetime in the bulk HVPE‐grown GaN revealed the presence of different‐size crystalline grains, with lifetime peaking up to 70 ns in the centers of the largest grains (～20 μm in diameter) and dropping to 10 ns in the small ones, while the spatially averaged lifetime was 40 ns. The inhomogeneity was ascribed to the interplay of nonradiative diffusion‐limited recombination at grain boundaries and a bulk lifetime in the crystallite centers. The numerical solution of spatially‐resolved carrier decay rate in the crystallite centers at high injection levels and comparison with experimental data provided a bulk nonradiative recombination time of ～70 ns. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

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.     

Stokes parameters measurement of light over a wide wavelength range by judicious choice of azimuthal settings of quarter-wave plate and linear polarizer

The Stokes parameters (S_p, S₁, S₂, S₃) of light are measured at an arbitrary wavelength over a wide wavelength range. The Stokes parameters S₁ and S₂ are easily obtained. But the Stokes parameter S₃ at the arbitrary wavelength is affected by the phase difference error Δ₁ of the quarter-wave plate mismatch and the Stokes parameters S₁ or S₂. Therefore, in this paper, S₃ is obtained from both the intensity measurements by the circular polarizer rotating the quarter-wave plate by 0° and 90°. Then, S₃ is obtained by considering only Δ₁, but is not affected by S₁ and S₂. Also, though Δ₁ is not accounted for, S₃ is measured more accurately.     

Nuclear properties of Z=114 isotopes and shell structure of ~(298)114

The two-neutron separation energies(S_(2n)) and α-decay energies(Q_α) of the Z=114 isotopes are calculated by the deformed Skyrme-Hartree-Fock-Bogoliubov(SHFB) approach with the SLy5,T22,T32 and T43 interactions.It is found that the tensor force effect on the bulk properties is weak and the shell closure at N=184 is seen evidently with these interactions by analyzing the S_(2n) and Q_α evolutions with neutron number N.Meanwhile,the single-particle energy spectra of ~(298)114 are studied using the spherical SHFB approach with these interactions to furthermore examine the shell structure of the magic nucleus ~(298)114.It is shown that the shell structure is almost not changed by the inclusion of the tensor force in the Skyrme interactions.Finally,by examining the energy splitting of the three pairs of pseudospin partners for the protons and neutrons of ~(298)114,it is concluded that the pseudospin symmetry of the neutron states is preserved better than that of the proton states and not all of the pseudospin symmetries of the proton and neutron states are influenced by the tensor force.     

The angular intensity correlation functions C(1) and C(10) for the scattering of light from randomly rough dielectric and metal surfaces

We study the statistical properties of the scattering matrix S(q|k) for the problem of the scattering of light of frequency ω from a randomly rough one-dimensional surface, defined by the equation x₃=ζ(x₁), where the surface profile function ζ(x₁) constitutes a zero-mean, stationary, Gaussian random process. This is done by studying the effects of S(q|k) on the angular intensity correlation function C(q,k|q',k')=〈I(q|k)I(q'|k')〉-〈I(q|k)〉〈I(q'|k')〉, where the intensity I(q|k) is defined in terms of S(q|k) by I(q|k)=L^-1₁(ω/c)|S(q|k)|², with L₁ the length of the x₁ axis covered by the random surface. We focus our attention on the C⁽¹⁾ and C⁽¹⁰⁾ correlation functions, which are the contributions to C(q,k|q',k') proportional to δ(q-k-q'+k') and δ(q-k+q'-k'), respectively. The existence of both of these correlation functions is consistent with the amplitude of the scattered field obeying complex Gaussian statistics in the limit of a long surface and in the presence of weak surface roughness. We show that the deviation of the statistics of the scattering matrix from complex circular Gaussian statistics and the C⁽¹⁰⁾ correlation function are determined by exactly the same statistical moment of S(q|k). As the random surface becomes rougher, the amplitude of the scattered field no longer obeys complex Gaussian statistics but obeys complex circular Gaussian statistics instead. In this case the C⁽¹⁰⁾ correlation function should therefore vanish. This result is confirmed by numerical simulation calculations.