皮秒激光辐照下半导体表面结构变化的研究

研究了皮钞激光辐照下，半导体吸收和反射特性与材料性质、激光能量密度及激光产生电子-空穴等离子体的关系。实验测量了硅材料与掺杂硅材料表面反射率与Nd:YAG锁模激光器能量密度的关系曲线，给出了分析靶面结构的方法。     

皮秒激光加工研究进展与展望

皮秒激光加工作为一种先进的超快加工技术,以其“冷加工”、高重复频率和高脉冲能量等特点,可实现对多种材料高精度、高效率的微细加工,在精密机械、表面工程、生物医学等领域具有广阔的应用范围和前景。综述了皮秒激光用于金属薄板及硬脆性材料的微孔加工、切割划线以及用于钛酸锶、氧化锆等材料表面改性方面的研究进展,从工艺参数优化、配套装备改进等方面探讨了皮秒激光加工现阶段存在的问题及发展方向。     

皮秒激光在熔融石英中诱导微爆炸形成微腔的研究

介绍了皮秒激光诱导损伤的实验与理论研究。熔融石英置于硅基上,利用皮秒激光脉冲聚焦于硅与熔融石英的接触界面,在熔融石英内部诱导等离子体,并加工出微通道和微腔。在显微镜下观察,微通道和微腔的周围没有发现热裂纹,微腔的直径范围从1.5~5 μm。分析了损伤的形成机理,建立模型讨论微腔的形成机理和大小特征。石英吸收激光能量形成等离子体,等离子体的形成和膨胀将产生冲击波,并受到周围介质的限制,在一个很小的体积内诱导微爆炸,受限的微爆炸在材料内部形成微腔。最后分析了微腔的分布特征。     

高功率可调谐皮秒光纤激光产生技术

实验研究了一种基于增益开关激光二极管和掺镱光纤放大器的高功率可调谐皮秒激光脉冲产生技术与系统.采用增益开关激光二极管作为种子源,多级掺镱单模光纤预放大器和两级大模场双包层掺镱光纤主放大器构成的放大系统,以及增益补偿技术、可调谐滤波技术、Sagnac环技术和包层泵浦技术相结合的方法,获得了中心波长1 053～1 073 ...     

晶体硅太阳能电池激光隔离pn结的研究

在晶体硅太阳能电池生产过程中,为了避免过低的填充因子,电池边缘多余的pn结必须去掉。首先利用激光温度场在硅材料中的分布,得出硅片在纳秒级脉冲激光作用下的融化峰值功率阈值。然后根据此阈值选择合适的激光器进行晶体硅太阳能电池激光隔离pn结的研究。通过激光隔离槽的3D形貌及测试太阳能电池的反向电流和并联电阻寻找最佳激光隔离的工艺参数。通过实验证明,纳秒级脉冲激光隔离能达到并超过化学隔离及等离子隔离的效果,为太阳能电池pn结隔离提供一种经济、环保的方案。     

五甲氧基红的吸收光谱和皮秒激光光谱研究

进行了五甲氧基红(2、4、2′、4′、2″—五甲氧基三苯甲醇)吸收光谱和皮秒激光荧光光谱研究。发现在酸性低粘度醇类溶剂中,五甲氧基三苯甲基正离子的褪色现象。对其褪色机理及溶剂粘度对于五甲氧基红皮秒激光光谱的影响进行了讨论。     

蓝宝石片的皮秒激光划片工艺研究

由于具有硬度高、热导低及脆性大的特点,蓝宝石材料的精细加工较为困难。对皮秒脉冲激光用于蓝宝石片划片的特点进行了分析和讨论。在此基础上,对用于红外焦平面组件封装的蓝宝石片的皮秒激光划片参数进行了研究,并得到了一系列优化参数。对于红外焦平面阵列封装中常用的厚度为0.4 mm的蓝宝石过渡电极板,在组合划片参数为P(100) X(0.01/20) Y&Z(12) Z(0.1/3)时达到了最佳划片效果。分析了激光功率参数变化对划片的影响,并对实际划片操作中的一些问题进行了探讨。     

皮秒激光加工工艺对微沟槽表面的疏水性研究

为了研究紫外皮秒激光在均热板基板表面刻蚀微沟槽后,不同激光工艺参数对微沟槽表面疏水性的影响规律,采用Cassie-Baxter模型进行了理论分析,并利用单因素实验法,改变激光扫描速率、激光扫描间距、光斑横向重叠次数进行实验验证.结果表明,降低固-液区域面积占比、宽度或缩短沟槽间距,均可以提升微沟槽表面的疏水性能;造成微...     

高能纳秒激光烧蚀单晶硅的微观结构

高能纳秒激光烧蚀硅时,往往会伴随着相爆炸过程,它决定了烧蚀的形貌特征。基于相爆炸的物理过程,分析了相应的烧蚀形貌：相爆炸的发生会使得硅材料发生大范围的去除,高温熔化材料的混合物向外喷溅,冷却形成放射状的冷却条,期间分布着冷却的球状微粒;超热液体的去除部位形成一个类似花瓣状坑,在坑中由于入射光与散射光的干涉形成条纹,其周期与激光光波相似。     

Excimer laser junction of crystalline silicon solar cells

An excimer laser cut trench is an effective means of providing junction isolation between the n⁺ diffused region and the aluminium back contact of a crystalline silicon solar cell. This method was developed for processing of edge-defined film-fed growth (EFG) silicon ribbon solar cells and has several features that make it attractive for low-cost solar cell processing. It is a single-step, noncontacting, dry process which is conducted in air. Only 100 laser pulses are required for isolation along a 10-cm line of focus, which permits a high throughput for this process. This technique should also be applicable to other types of crystalline solar cell where cell junctions are formed by a thermal diffusion process     

Effect of binding force between silver paste and silicon on power degradation of crystalline silicon solar module

The long term reliability of crystalline solar modules is critical to the cost effectiveness and the commercial success of photovoltaic. The binding force reduction between silver paste and silicon leads to power degradation during subsequent qualification tests or outdoor using. Hence, it is very important to investigate the binding force of busbar and its influence. In this paper, the relationship between power degradation and the binding force of busbar was investigated. Significant results about binding strength of busbar were found as a result of different silver pastes. For crystalline silicon solar cells with 1.6 mm width busbar, the binding force between silver paste and silicon is not less than 2.0 N so as to let the modules made by such cells pass qualification tests. The results laid the foundation for studying the mechanical performance of front contact metallization system for screen-printed crystalline silicon solar cells.     

强激光系统中硅镜变形数值分析

本文运用数值传热学中全隐差分格式交替方向块迭代法,对周边绝热强激光照射非稳态条件下硅镜的温度及挠变形进行了数值模拟,给出了形变随激光功率、光斑直径、镜片直径、镜片厚度以及照射时间等参数的变化规律,并对镜片局部最高温度的变化作了探讨和分析.     

Simulation of the absorption of a femtosecond laser pulse in crystalline silicon

The effect of the nonlinearity of the absorptivity and absorption coefficient on the process of the intense photoexcitation of silicon is studied on the basis of a model of the two-photon excitation of a semiconductor with consideration for external emission. Correlation between the results of simulation of the absorption of a femtosecond laser pulse in single-crystal silicon and experimental data under conditions of the femtosecond excitation of surface plasmon polaritons makes it possible to refine the mechanism of changes in the absorptivity and to make an inference regarding the necessity of considering these changes when assessing the conditions of the laser treatment of semiconductors. Avenues for further improvement of the theoretical model are discussed.     

Influence of precursor layer ablation on laser doping of silicon

This paper presents a numerical model, which quantitatively demonstrates that ablation and partial recondensation of the dopant precursor layer are some of the dominating physical processes in laser doping (LD) of crystalline silicon. Our pulsed LD process uses a line focused laser beam, enabling the creation of solar cell emitters without the generation of dislocations, if the width w of the short axis of the line focus is w < 10 μm. The concentration profiles of the dopant atoms strongly depend on the pulse energy density E_p, the pulse to pulse separation Δx and the number of laser scans N_s. By comparing measured with modeled concentration profiles, we are able to evaluate the ablation width as well as the amount of the ablated precursor layer. In case of a sputtered phosphorus precursor layer, the ablation width w_a is w_a = 6 μm, whereas the width of the molten silicon layer w_m is w_m = 5 μm. The model also explains the dependence of experimental dopant concentration profiles on the number of subsequent laser scans N_s and pulse to pulse separation Δ_x. Copyright © 2010 John Wiley & Sons, Ltd.     

Geographical variation of the conversion efficiency of crystalline silicon photovoltaic modules in Europe

We present a geographical assessment of the performance of crystalline silicon photovoltaic (PV) modules over Europe. We have developed a method that is based on a material specific analytical expression of the PV conversion efficiency, relative to nominal efficiency, as a function of module temperature and irradiance. This method is combined with a climate database that includes average daytime temperature and irradiance profiles. It is found that the geographical variation in ambient temperature and yearly irradiation causes a decrease in overall yearly PV performance from 3 to 13% relative to the performance under Standard Test Conditions, with the highest decrease found in the Mediterranean region. Based on the above results we developed a simplified linear expression of the relative PV module efficiency that is a simple function of yearly total irradiation and yearly average daytime temperature. The coefficients to the linear expression are found by fitting to the map resulting from the above‐mentioned analytical approach. The prediction of total yearly PV output from this linear fit deviates less than 0·5% from the more detailed calculation, thus providing a faster and more simplified alternative to the yield estimate, in the case when only limited climate data are available. Copyright © 2008 John Wiley & Sons, Ltd.     

激光可视检漏仪中激光能量对灵敏度的影响

目前,六氟化硫激光可视检漏仪在电力行业的六氟化硫检漏方面得到了初步的应用,这类仪器的灵敏度受到各种因素的影响。本文详细分析了激光功率对仪器灵敏度的影响,提出了激光功率对灵敏度影响的简化数学模型。     

Theoretical approach to estimate laser process parameters for drilling in crystalline silicon

This paper presents a simple method for estimating the ablation rate during drilling processes in crystalline silicon wafers. Using data from literature, the physical process of material heating, melting, and ejection can be estimated on a time scale and leads to a temporal separation of the pulse duration in two parts. The latter one offers a theoretical determination of the expected average ablation rate. The results of this approximation coincide with experimental values and offer solutions to increase drilling efficiency. The experiments were done with a q‐switched solid‐state laser emitting at 1064 nm wavelength at pulse durations between 810 ns and 1440 ns. Copyright © 2010 John Wiley & Sons, Ltd.     

Mechanism of breakdown voltage wavering in power MOSFET induced by silicon crystalline defect

This paper presents the impact of silicon crystalline defects generating mechanism of breakdown voltage degradation on low voltage vertical Power N-MOSFETs, functioning in avalanche mode. The physical defect determination is presented through a full failure analysis: it includes specific sample preparation, electrical characterization using EMMI techniques and physical characterizations using Scanning Electron Microscope, Transmission Electron Microscope and chemical delineation etches. Silicon crystal defects (edge dislocation and stacking fault) are found to be at the origin of the failure. Then, a discussion presents how the failure mechanism impacts the device structure and some possible root cause at the origin of the defect.