半导体材料少子寿命测试仪的研制开发

少数载流子寿命(简称少子寿命)是半导体材料的一项重要参数，它对半导体器件的性能、太阳能电池的效率都有重要的影响。我们采用微波反射光电导衰减法研制了一台半导体材料少子寿命测试仪，本文将对测试仪的实验装置、测试原理及程序计算进行了较详细的介绍，并与国外同类产品的测试进行比较，结果表明本测试仪测试结果准确、重复性高，适合少子寿命的实验室研究和工业在线测试。     

晶体硅太阳能电池少子寿命测试方法

少数载流子寿命(简称少子寿命)是半导体晶体硅材料的一项重要参数,它对半导体器件的性能、晶体硅太阳能电池的光电转换效率都有重要的影响。分别介绍了常用的测量晶体硅和晶体硅太阳电池少子寿命的各种方法,包括微波光电导衰减法(MW-PCD),准稳态光电导方法(QSSPC),表面光电压(SPV),IR浓度载流子浓度成像(CDI),调制自由载流子吸收(MFCA)和光束(电子束)诱导电流(LBIC,EBLC),并指出了各种方法的优点和不足。     

硅单晶中非平衡载流子寿命与注入水平的关系研究

阐述了硅单晶中非平衡载流子寿命与注入水平的函数关系以及少子寿命与复合寿命的区别,通过变光强测量得到一组寿命与注入水平的实测数据,用拟合法求得少子寿命及复合寿命与注入水平的函数曲线,所得结果与S-R-H理论模型相符.根据理论与实验成果,提出改进寿命测试一致性的方案,同时为发行少子寿命标准样品奠定了基础.     

弛豫半导体的表征与应用研究进展

介电弛豫时间大于载流子寿命的半导体为弛豫半导体,反之为寿命半导体。因为介电弛豫时间正比于电阻率,所以弛豫半导体一般为高阻半导体,例如补偿半导体、非晶半导体或低温下的半导体。在弛豫半导体中,由于材料恢复电中性的过程慢于载流子浓度恢复质量作用定律的过程,所以必须考虑空间电荷,包括自由电荷和陷阱所带电荷,对载流子输运的影响。少子注入会导致弛豫半导体多子耗尽、寿命半导体多子增加;中性注入会导致弛豫半导体电子空穴分离、寿命半导体发生双极性输运。弛豫半导体的多子耗尽现象可用电流-电压测试和交流响应测试进行表征,发现其电流-电压特性由低电压下的扩展线性区和高电压下的超线性区构成,且受陷阱浓度影响。使用载流子动力学测试可直接观察到弛豫半导体中光注入电子和空穴的分离现象。弛豫半导体独特的电学性质在辐射探测器、抗辐照器件、光电导开关、温度传感器等领域有广阔的应用价值。     

大注入水平下少子寿命的数值计算与分析

实现表面光电压法(SPV)在大注入水平下的少子寿命测量对表面光电压技术的应用和准确测量具有重要意义。本文计算了P型单晶硅片三种复合机制下注入水平与体寿命及表面复合率的关系。结果表明随着注入水平提高,主导复合机制发生改变,且少子寿命并不是一直随注入水平的增加而增加,而与杂质能级位置有关,表面复合率则恰好相反。为验证计算结果,对P型单晶硅片进行了注入水平可调的少子寿命测试。通过样品表面钝化,分离体表寿命,分别得到了注入水平与少子寿命和表面复合率的实验变化关系。理论计算结果与实验数据在测试范围内一致。     

高效单晶硅太阳电池基区结构设计与参数优化

首先利用TCAD半导体器件仿真软件全面系统地分析了在不同少子寿命的情况下,基区电阻率对常规P型单晶硅太阳电池输出特性的影响。然后基于对仿真结果的分析,提出一种具有非均匀基区的单晶硅太阳电池结构,并对其输出特性进行了仿真研究。结果表明:当少子寿命一定时,存在最优的基区电阻率,使得常规电池的转换效率最大;随着少子寿命的减小,电池最优的基区电阻率减小;提高基区电阻率有利于常规电池长波段量子效率和短路电流的提高,但同时会降低电池的开路电压和填充因子;当少子寿命较低时,非均匀基区结构不具有提高常规电池转换效率的作用。但当少子寿命增大到一定值时,通过优化非均匀基区的表面浓度,非均匀基区结构可有效改善常规电池的电学性能。     

射频功率对非晶硅膜固相晶化效果的影响

于不同射频功率下制备出非晶Si膜并对其进行真空退火处理,采用XRD、TEM和少子寿命测试仪等检测手段分析了退火前后薄膜的微观结构及电学性能。研究发现,随着射频功率的增加,薄膜的中程有序度和少子寿命均呈先增后减的趋势。经真空退火处理后,非晶硅膜得以晶化,少子寿命较退火前有大幅提高;另外,退火后薄膜的晶化率和少子寿命随射频功率的变化趋势与退火前一致,说明同一热力学条件下薄膜的中程有序度越高越容易发生晶化。     

半导体Si载流子迁移率的统计模型计算模拟

半导体材料栽流子迁移率是表征其电导特性的重要参数,在半导体材料载流子散射机制理论基础上,基于玻耳兹曼方程和Mathiessen规则,通过对具有不同热运动速度的载流子漂移速度求统计平均值,建立了Si材料栽流子迁移率的玻耳兹曼统计模型.计算了模拟载流子迁移率的影响因素和变化规律,并得出电场作用下的饱和漂移速度为-Vdn=1.1×107cm/s, -Vdn=8.7×106cm/s,与基于实验数据的经验公式导出的结果基本一致,表明玻耳兹曼统计模型具有良好的适用性.     

Ⅱ-Ⅵ族材料在叠层太阳能电池中的应用

Ⅱ-Ⅵ族材料ZnSe、CASe、ZnTe、CdTe等具有禁带宽度大,少子寿命对位错不敏感等优点,可以作为一种新的材料体系应用于叠层太阳能电池中.此类材料既能够与铜铟镓硒电池、Ⅲ-V族材料、单晶Si等相结合,也可将不同的Ⅱ-Ⅵ族材料相结合制备多结电池.本文介绍了上述几种思路的理论及实验研究现状,以及 Ⅱ-Ⅵ族材料顶电池的研究进展;同时分析了阻碍Ⅱ-Ⅵ族半导体材料应用的单极性掺杂问题,介绍了提高掺杂水平可能的途径.     

探索优化光电极中载流子传输的策略

将太阳能转化成氢能来发展氢能源经济是人类社会可持续发展的必由之路。光电化学分解水制氢是太阳能-氢能转换中具有重要应用前景的技术。经过近50年的发展,光电化学分解水制氢技术遇到了瓶颈,主要是缺乏高效稳定的光电极。近年来,通过沉积TiO x保护层的策略,部分光电极的稳定性得到了显著提升,因此,提高光电极的太阳能-氢能转换效率成为一项愈加重要的任务。其中,改善光电极载流子传输能够有效地提高太阳能-氢能转换效率。着重讨论了几种改善光电极中载流子传输的策略:制备有利于载流子扩散和迁移的纳米结构;通过掺杂提高材料的导电性;通过制备工艺的优化减少阻碍载流子传输的缺陷;构建半导体结;使用与材料多子输运匹配的导电衬底或引入少子阻隔层等。     

Studies of photoconductance decay method for characterization of near-surface electrical properties of semiconductors

The Photoconductance Decay (PCD) method in a standard version allows determination of the bulk properties of semiconductors but is not suitable for evaluation of the surface and near-surface region of the wafer during processing. This experiment is concerned with PCD measurements devised specifically for the purpose of electrical probing using temporary contacts of the near-surface (ns-PCD) region of semiconductor substrates, including thin films. The method is tested through the measurements of the single-crystal, indirect bandgap elemental semiconductor wafers (Si and Ge), as well as selected direct bandgap compound semiconductor wafers (GaAs and InP). In the former case, surface properties of the material tested are altered in a controlled fashion and the PCD response to the surface alteration, in terms of the minority carrier lifetime, is measured. In the case of all substrates studied, a direct correlation between carrier lifetime measured using PCD and the condition of the wafer surface was observed. Furthermore, the ns-PCD method was proven very effective in measuring minority carrier lifetime at the semiconductor-dielectric interface without having to form MOS test structures. The results obtained suggest that the modified PCD method employing temporary contacts to the measured surface can be used to monitor the condition of semiconductor surfaces during device processing.     

晶体面缺陷对FeS2薄膜电学性能的影响

采用Fe膜热硫化技术制备了具有不同比表面积和比晶界面积的FeS2薄膜,并测定其载流子浓度和电阻率,研究了FeS2薄膜表面和晶界等面缺陷对FeS2薄膜电学性能的影响.结果表明,表面和晶界两种面缺陷对FeS2薄膜的电学性能有类似的影响规律.在一定范围内,随着薄膜比表面积和比晶界面积的增大,载流子浓度提高而电阻率下降.面缺陷数量的变化可导致FeS2晶体中点缺陷数量、禁带中缺陷能级密度、不充分相变产物比例和相变应力水平的变化,从而导致载流子浓度和电阻率的变化.     

Carrier Transport Parameter Imaging in a Multicrystalline Silicon Solar Cell by Laser-Induced Photocarrier Radiometry

The distribution of minority carrier transport parameters (i.e., minority carrier lifetime, diffusion coefficient, and two surfaces recombination velocities) of multicrystalline silicon (mc-Si) solar cell was investigated using laser-induced photocarrier radiometry (PCR). Images of the amplitude and phase of the PCR measurements clearly showed the crystal boundaries of the mc-Si solar cell. The distribution of minority carrier transport parameters was obtained by best fitting the experimental results to the theoretical two-layer carrier density wave model of solar cells. The best-fitting results demonstrated that there was great difference in the minority carrier transport parameters among various grains.     

Fast,high resolution,inline contactless electrical semiconductor characterization for photovoltaic applications by microwave detected photoconductivity

The state-of-the art lifetime measurement technique MDP (microwave detected photoconductivity) is presented with its latest developments in sensitivity, measurement speed and data simulation. Several applications and examples in the field of inline material characterization, defect recognition and real time statistical process control in silicon bricks and wafers are presented, demonstrating the practical use of MDP measurements and of the data obtained by it. The measured lifetime itself combined with its spatial distribution and the measured steady state photoconductivity enable a good correlation to the cell efficiency. Furthermore, the paper presents a detailed summary of the properties of steady state and non-steady state microwave based minority carrier lifetime measurement techniques to complete this extensive study.     

Surface passivation of multicrystalline silicon wafers by porous silicon combined with an ultrathin nanoparticles aluminum coating film

In this paper, we demonstrate that we may efficiently improve surface passivation of multi-crystalline silicon (mc-Si) while combining formation of porous silicon (PS) and deposition of ultrathin aluminum (Al) film. Aluminum Nanoparticles were deposited by thermal evaporation onto PS formed on mc-Si wafers. Optoelectronic properties of Al/PS/mc-Si and Al/mc-Si treated samples were investigated before and after annealing in the 400–700 °C temperature range. The surface passivation effectiveness was pointed out based on minority carrier lifetime and photoluminescence measurements. It was found that, at a minority carrier density Δn = 10¹⁵ cm^?3, the effective minority carrier lifetime increases from 1.5 μs (for the bare mc-Si wafer) to about 6 and 14 μs before and after thermal annealing, respectively. FTIR analyses show strong correlation between the minority carrier lifetime values and hydrogen and Al passivation. Major beneficial effect of the co-presence of Al and Al–O on the optoelectronic properties is also demonstrated. The reflectivity of Al/PS treated mc-Si decrease significantly at 500 nm as compared to untreated mc-Si (from 31 % for untreated mc-Si wafers to 8 % for Al/PS treated ones), which is due to the roughly ordered structure and to the Al nanoparticles.     

Quantitative Carrier Density Wave Imaging in Silicon Solar Cells Using Photocarrier Radiometry and Lock-in Carrierography

InGaAs camera-based low-frequency homodyne and high-frequency heterodyne lock-in carrierographies (LIC) are introduced for spatially resolved imaging of optoelectronic properties of Si solar cells. Based on the full theory of solar cell photocarrier radiometry (PCR), several simplification steps were performed aiming at the open circuit case, and a concise expression of the base minority carrier density depth profile was obtained. The model shows that solar cell PCR/LIC signals are mainly sensitive to the base minority carrier lifetime. Both homodyne and heterodyne frequency response data at selected locations on a mc-Si solar cell were used to extract the local base minority carrier lifetimes by best fitting local experimental data to theory.     

透明导电膜ZnO:Al(ZAO)的组织结构与特性

ZnO:Al(ZAO)是一种简单并半导体氧化物薄膜材料，具有高的载流子浓度和光学禁带宽度，因而具有优异的电学和光学性能，极具应用价值，对于其能级高度简并的ZAO半导体薄膜材料，在较低的温度下，离化杂质散射占主导地位，在较高的温度下，晶格振动散射将成为主要的散射机制；晶界散射仅当晶粒尺寸较小（与电子的平均自由程相当）时才起作用，本文分析了ZAO薄膜的制备方法，晶体结构特性，电子和光学性能以及载流子的散射机制。     

Effects of DC Current on the Mechanical Behavior of AlMg1SiCu

The effect of an electron wind on the mechanical properties of aluminum is investigated with the ultimate goal of establishing a technique by which the mechanical energy associated with the deformation of a material can be reduced without requiring a significant increase in the material's temperature. In the study presented herein, the effect that the electrical flow has on the mechanical properties of aluminum is examined through tensile testing. However, as electricity is passed through the material, some incidental resistive heating occurs. Therefore, in order to isolate the effect of the electrical flow from that resulting from resistive heat, the effect of transient temperatures on the stress-strain behavior of aluminum is also considered, with, and without, the presence of the electrical flow. In addition, variation in the electrical effect, with respect to the aluminum's temper and electrical pre-treating, is investigated. The experimental results indicate that the electrical current has the potential to substantially reduce deformation energies without causing significant increases in the workpiece temperature. The data also indicates that this effect exists regardless of the temper on the material. Finally, the study found that electrically pre-treating the aluminum produced results similar to that of an annealing process (i.e., the energies were significantly reduced).