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.     

Combined frequency- and time-domain photocarrier radiometry characterization of ion-implanted and thermally annealed silicon wafers

A combined frequency-swept and quasi-time-domain photocarrier radiometry (PCR) technique was developed to characterize thermally annealed silicon wafers with B+ , P+ , and As+ ion implantation at doses ranging from 1 × 1011 cm-2 to 1 × 1016 cm-2 . The implantation dose dependence of the PCR amplitude, the frequency dependencies of the PCR amplitude and phase, as well as the quasi-time-domain PCR waveforms were simultaneously employed to analyze all the ion-implanted silicon samples. The dependence of the effective lifetime on the implantation dose has been investigated and shown to be related to the trap density and the lifetime extracted from the transient PCR signals.     

Photoacoustic and photothermal radiometry spectra of implanted Si wafers

The effects of Ar⁺⁸ and O⁺⁶ ion implantation of Si were investigated by photoacoustic (PA) and photothermal radiometry (PTR) methods. The surface of Si sample was treated with Ar⁺⁸ or O⁺⁶ ions with various doses. Amplitude and phase PA spectra of Si with and without ion-implantation were measured and analyzed in the wavelength range from 800 to 1600 nm (the energy range from 0.75 to 1.55 eV) and frequency of modulation, from 1 Hz to 100 kHz.     

Investigation of H<Superscript>+</Superscript> implanted silicon wafers with two-beam cross-modulation photocarrier radiometry

Single beam laser-induced infrared photocarrier radiometry (PCR) has been applied for measuring transport properties of H⁺ ion-implanted silicon samples. The contrast between the PCR signals inside and outside the area of implantation was investigated for different doses and energies of implantation. The H⁺ ion-implantation range of doses and energies was 3×10¹⁴ cm^-2 - 3×10¹⁶ cm^-2 and 0.75 MeV–2 MeV, respectively. Furthermore, a two-beam cross-modulation PCR technique was introduced to perform the same type of measurements inside and outside the implanted area. Comparison between contrasts from single- and double-beam methods showed significantly higher degree of sensitivity for the two-beam PCR technique.     

Femtosecond laser micromilling of Si wafers

Femtosecond laser micromilling of silicon is investigated using a regeneratively amplified 775 nm Ti:Sapphire laser with a pulse duration of 150 fs operating at 1 kHz repetition rate. The morphological observation and topological analysis of craters fabricated by single-shot laser irradiation indicated that the material removal is thermal in nature and there are two distinct ablation regimes of low fluence and higher fluence with logarithmical relations between the ablation depth and the laser fluence. Crater patterns were categorized into four characteristic groups and their formation mechanisms were investigated. Femtosecond laser micromilling of pockets in silicon was performed. The effect of process parameters such as pulse energy, translation speed, and the number of passes on the material removal rate and the formation of cone-shaped microstructures were investigated. The results indicate that the microstructuring mechanism has a strong dependence on the polarization, the number of passes and laser fluence. The optimal laser fluence range for Si micromilling was found to be 2-8 J/cm² and the milling efficiency attains its maximum between 10 and 20 J/cm².     

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.     

气体辐射太赫兹波产额与驱动激光强度的依赖关系

利用光电流模型研究了气体辐射太赫兹波产额与驱动激光峰值强度的依赖关系.模拟表明,无论是单色激光脉冲还是双色激光场,当激光较弱时,太赫兹产额随着激光强度的增加而迅速增大;而当气体电离接近或达到饱和后,进一步增强激光场强度,太赫兹产额出现了振荡变化.与通常采用较弱激光强度相比,更高的激光强度(致使气体达到完全电离)会进一步增强太赫兹波的辐射强度.分析各个电离事件所产生电子的个数和运动轨迹的对称性,可以很好地解释这些结果.     

Thin-film formation of Si clathrates on Si wafers

In this study, we prepared Si clathrate films (Na₈Si₄₆ and Na_xSi₁₃₆) using a single-crystalline Si substrate. Highly oriented film growth of Zintl-phase sodium silicide, which is a precursor of Si clathrate, was achieved by exposing Na vapour to Si substrates under an Ar atmosphere. Subsequent heat treatment of the NaSi film at 400 °C (3 h) under vacuum (<10⁻² Pa) resulted in a film of Si clathrates having a thickness of several micrometres. Furthermore, this technique enabled the selective growth of Na₈Si₄₆ and Na_xSi₁₃₆ using the appropriate crystalline orientation of Si substrates.     

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.     

Reconstruction of the radial dependence of the structural characteristic of the refractive index in a supersonic gas flow from laser beam intensity fluctuations

A method for reconstructing the radial dependence of the structural characteristic of the refractive index of air in an axisymmetric supersonic gas flow from the variance of intensity fluctuations of a laser beam that is transmitted through the flow at different distances from the jet symmetry axis is proposed. An expression that relates the relative intensity variance on the beam axis as a function of the aiming distance and the radial dependence of the structural characteristic is obtained. To invert this expression, the Abelian transformation is used. The parameters of the jet module of an AT-326 wind tunnel at the Institute of Theoretical and Applied Mechanics of the Siberian Branch of the Russian Academy of Sciences are modeled.     

Acousto-optic stabilization of the intensity of a laser beam

A system for stabilization of the intensity of a laser beam based on an acousto-optic modulator is theoretically and experimentally studied. An equation that describes dynamic processes in the system and various working regimes is derived. It is demonstrated that the stabilization coefficient depends on the transfer coefficient of the feedback circuit and the position of the working point on the amplitude characteristic of the acoustooptic interaction. An experimental prototype of the stabilization system is based on a paratellurite acousto-optic cell. The system stabilizes the intensity with a coefficient of 78 in a frequency band of 15–180 Hz.     

Wavelength dependence of intensity fluctuations in laser speckle patterns from biological specimens

Speckle patterns obtained when botanical specimens are illuminated with laser light are observed to fluctuate at a rate which depends on the wavelength of the light used. It is suggested that this wavelength dependence may be of value as an additional degree of freedom in some applications of intensity fluctuation spectroscopy.     

Threshold dependence of the vibrational excitation of molecules on laser radiation intensity

The collisionless vibrational excitation of a polyatomic molecule in an IR laser radiation field has been theoretically studied. It has been shown that (i) the degree of vibrational excitation (namely, number 0000 of vibrational quanta of a molecular mode near-resonant with the IR laser field that are absorbed by the molecule) is low if laser pulse intensity P (energy flux density in the laser beam) is lower than a certain critical value P _cr; (ii) the degree of excitation abruptly increases after crossing the boundary where P = P _cr; (iii) this effect is attributed to two properties inherent in polyatomic molecules, namely, the anharmonicity of the vibrational mode interacting with the laser field and the energy exchange with other modes; and (iv) at P > P _cr, number 00000 is determined only by energy density Φ = Pτ_P, where τ_P is the laser pulse duration, 00000 monotonically increases with increasing Φ. The model is in good agreement with the experimental data.     

Measurement of the laser beam intensity distribution using optical tomography

Optical tomography is proposed as a method for studying the intensity distribution in the laser beam cross section. The tomographic projection of the beam cross section is obtained with the help of an optical fiber possessing a high radiation resistance, which makes it possible to employ this technique for studying high-power laser radiation. The results of tomographic reconstruction of the bean cross section from experimental projections are compared with the results of reconstruction from model projections.     

基于自适应光学技术控制光束近场场强

在双变形镜自适应光学系统中,需要主激光出射时与信标光的振幅分布一致、相位共轭,当主激光到达目标时光波的分布与目标上发射的信标光光波分布相同,主激光的振幅和相位都得到校正。根据双变形镜自适应光学技术的概念,提出一种基于自适应光学技术控制光束近场场强的方法,从而实验验证双变形镜技术的可行性。该方法利用哈特曼传感器探测到的波前信息,对变形镜进行控制,实现了对光束近场场强的控制。仿真结果表明该系统对光束近场强度能进行较好地校正,使校正前后光束振幅的残余均方差值从0.310 0降为0.052 2,同时实验也验证了这种方法的可行性。     

基于自适应光学技术控制光束近场场强

在双变形镜自适应光学系统中,需要主激光出射时与信标光的振幅分布一致、相位共轭,当主激光到达目标时光波的分布与目标上发射的信标光光波分布相同,主激光的振幅和相位都得到校正。根据双变形镜自适应光学技术的概念,提出一种基于自适应光学技术控制光束近场场强的方法,从而实验验证双变形镜技术的可行性。该方法利用哈特曼传感器探测到的波前信息,对变形镜进行控制,实现了对光束近场场强的控制。仿真结果表明该系统对光束近场强度能进行较好地校正,使校正前后光束振幅的残余均方差值从0.310 0降为0.052 2,同时实验也验证了这种方法的可行性。     

Light-polarization and intensity dependence of higher-order nonlinearities in excitonic FWM signals

A theory-experiment comparison for the intensity and polarization dependence of spectrally resolved transient four-wave-mixing signals is presented for a ZnSe single quantum well. Results for high intensities deviate from a simple model based on the optical Bloch equations for a five-level system whereas a microscopic theory for coherent excitonic and biexcitonic nonlinearities shows excellent agreement.Received: 8 July 2004, Published online: 14 December 2004PACS: 71.35.-y Excitons and related phenomena - 78.47. + p Time-resolved optical spectroscopies and other ultrafast optical measurements in condensed matter     

非均匀激光辐照下硅镜热变形对光束传输特性的影响

 使用有限元法计算了硅镜在DF化学激光器非稳腔输出的中空非均匀激光辐照下镜面温升和反射面面形随时间变化的特性,使用65阶Zernike多项式对镜面面形进行了曲面拟合,使用光线追迹的方法计算了平行光束经不同数量硅镜反射后的光束波前分布PV值、Strehl比和Zernike像差系数随时间变化的特性。计算结果表明：在典型的DF激光器输出的中空方形光束辐照下,硅反射镜的热变形将使反射光束产生波前畸变,波前畸变中,y方向像散项占据主要地位,其次是离焦项;随着激光系统中反射镜面数量的增加,高阶像差系数将逐渐增大,且波前PV值与反射次数成线性关系。     

Focusing effect of a laser beam on the power dependence of multiphoton processes

The effect of focusing a laser beam on the intensity (I) dependence of multiphoton processes was examined. A general method is given to deduce a genuine intensity dependence from the focused-beam experiment. In addition, some typical examples were examined in detail. For the dependence of the type ofI ⁿ, an apparent relation ofI ^3/2 appears only when there is a change of dependence asI ⁿI^m, withn>3/2 andm<3/2. A genuine intensity dependence can be obtained directly from the focused beam experiment ifn does not change throughout the irradiated volume, or if the conditionn>3/2>m does not hold. The case of gradually decreasingn, as is common for the infrared multiphoton reaction probability (P), was also analyzed taking the Arrhenius-type dependence,P exp(–/I), as an example. A simple method is proposed to obtain a genuine relation betweenP andI for this type of intensity dependence.