硅在脉冲激光作用下温度积累效应的数值模拟

采用单温模型,利用有限元方法对硅在纳秒脉冲激光作用下的温度积累效应进行了数值模拟。给出了单脉冲、多脉冲作用下,硅表面附近的非平衡载流子浓度、自由载流子吸收系数和晶格温度随时间的变化规律。结果表明,自由载流子浓度的积累是温度积累的主要来源。对于多脉冲作用情况,脉冲间隔越短,脉宽越窄,温度积累效应越明显,最终形成的瞬时晶格最高温和温升值越大,越容易对材料造成损伤。     

硅的等离子体形成及相变微微秒时间分辨的探测

本文利用微微秒时间分辨的反射率与透射率的变化研究0.53μm约30ps脉冲激光激发的硅的电子-空穴等离子体形成及相变中的动态性质.实验结果证实了光能可以在小于30ps的时间内转移给晶格,晶格加热、相变可以在激光作用期间完成.实验指出,Auger 复合可以限制等离子体浓度的增加.从实验结果中还推导了高激光下等离子体的一些参量.     

超短脉冲激光烧蚀半导体表面的热效应分析

为了研究超短激光辐照下半导体表面的热效应,采用有限差分法对双温方程进行了数值模拟,研究了飞秒、皮秒激光作用下,半导体表面载流子和晶格的温度分布情况.结果表明,载流子与晶格的温度耦合时间和金属耦合时间大致相同,激光功率密度是影响载流子温升的主要因素,超短脉冲激光入射时能量主要被半导体表层载流子吸收,所得结论与实验结果较吻合.     

皮秒和纳秒脉冲激光作用于半导体材料的加热机理研究

从半导体材料的吸收机制出发,分析研究了激光能量在半导体材料中的传输过程,并采用双温模型分别模拟计算了在人射激光能量相同的情况下,皮秒和纳秒激光脉冲作用于硅半导体材料的加热过程,结果表明在纳秒脉冲作用下,可以忽略载流子效应,用单纯的单温热传导方程来模拟。而在皮秒脉冲作用下,应该考虑载流子效应,采用包括晶格温度和载流子温度的双温模型来模拟硅半导体材料的加热过程。     

热载流子注入对器件性能影响及其改善措施

当载流子在大于10~4V·cm~(-1)的电场下运动时,它从电场获得的能量大于散射过程中与晶格原子碰撞损失的能量,因而载流子的温度将会超过晶格温度.这样的载流子就称为热载流子.在VLSIC中,为了达到高速度和高集成度,设计时必须采用一系列的折衷方案.为了避免短沟道效应,增加了体掺杂浓度,以使较小的沟道长度的器件保证质量,获得小的亚阈值泄漏电流.由于驱动电流的降低,栅氧化层厚度也按比例缩小.减小沟道长度、减薄氧化层厚度以及相应增加了体掺杂浓度,这些综合结果有助于产生和注入热载流子.一旦晶体管表面反     

紧束缚带半导体中载流子浓度和费米能量解析近似研究

本文给出了紧束缚带半导体中载流子浓度和费米能量之间的解析近似表达式。借助贝塞尔函数我们获得载流子浓度的系列展开公式，该公式具有快速收敛性。采用高斯积分方法获得了简单和高精度的费米能量解析近似表达式。由解析公式计算的结果与精确数值解吻合得很好，精度为10^-5量级。该解析公式可以方便地用于计算微带超晶格的电子输运和超晶格器件模拟。     

高反Al2O3/SiO2膜内超快激光预损伤动力学过程

利用紫外飞秒激光光谱技术研究了Al2O3/SiO2高反射膜内的超快载流子动力学。通过实验,发现该反射膜Al2O3层的载流子动力学在紫外反射膜的激光诱导损伤中起着至关重要的作用。通过泵浦-探测实验,发现紫外飞秒激光与光学薄膜作用后,光学薄膜反射率有所下降,且探测光反射率变化的峰值在约2.3 ps的时间内从417 nm左右转移到402 nm左右。为了更好的解释激光诱导载流子动力学,一个具体的理论模型被提出来,该模型指出导带自由电子弛豫过程中与晶格相互作用,产生距导带一个光子能量的中间缺陷态,其初始电子密度影响了材料损伤阈值高低。通过该理论模型得出的激光损伤阈值数据和实验数据吻合得很好。     

飞秒激光作用下金属箔材的温度场研究

为分析飞秒激光作用下金属材料的温度场及其影响因素,基于一维双温模型对飞秒激光作用下铜箔的温度场进行数值求解。采用脉宽100～800 fs,能量密度509.30～2 546.48 J/m2的激光参数进行计算,研究电子和晶格温度随时间和深度的变化规律。结果表明,电子温度在10-13 s时间尺度达到峰值,在此期间晶格温度保持不变,此后通过耦合作用二者在几ps时间尺度达到热平衡;脉宽越短,电子温升越快、峰值温度越高、耦合时间越短;而能量密度越大,电子温升越快、峰值温度越高、耦合时间越长。     

黑硅薄膜的电学输运特性

采用飞秒激光在六氟化硫气氛中对硅表面进行扫描,在硅衬底上制备了具有超饱和硫重掺杂的黑硅薄膜。采用变温霍尔测试方法,在30~300 K温度范围内测试了黑硅薄膜-硅衬底双层结构的载流子浓度温度特性和迁移率温度特性。采用双层结构的霍尔载流子浓度模型和霍尔迁移率模型,从测试结果中分离出黑硅薄膜的载流子浓度温度特性和迁移率温度特性。采用杂质带电离载流子模型拟合黑硅薄膜的载流子浓度温度特性,得到黑硅薄膜的硫杂质带的中心能级为Eds=-159 meV,高斯半高宽为50.57 meV,有效硫浓度Nds=1.0cm-3×1020cm-3,室温下硫的电离率为7%。计算得到的杂质带态密度分布图,此时杂质带与导带开始融合,黑硅薄膜发生了绝缘体金属转化现象,并解释了黑硅薄膜载流子浓度温度特性中随温度升高激活能增大的现象。黑硅薄膜载流子迁移率特性说明,在低温下杂质散射是主要的散射机制,在高温下声子散射是主要的散射机制。并采用硅中载流子迁移率的经验模型,将黑硅薄膜载流子迁移率分离成导带电导和杂质带电导两部分,得到杂质带的迁移率μi在1~10 cm2/Vs。     

光导型光电探测器瞬变行为的仿真

较强功率的激光辐照半导体探测器时既产生光电效应又产生热效应，提出了反映光电效应的载流子输运模型和反映热效应的热扩散模型。计算了不同激光辐照功率密度下PC型HgCdTe探测器内的光生载流子浓度和热平衡载流子浓度．由此对探测器的瞬变行为进行了仿真计算。仿真结果与实验结果相吻合。     

Characterization of semiconductor devices by infrared laser interferometry

The principles of characterization techniques for semiconductor devices based on infrared laser interferometry are reviewed. Transient optical signals due to plasma-and thermo-optical effects are studied by experiment and numerical modeling, providing information on carrier concentration and lattice temperature in the device. The applicability of the techniques is demonstrated on smart power devices, VDMOSFETs, IGBTs and on sub-micron technology MOS- and bipolar transistors.     

Charge-carrier concentration and temperature in quantum wells of laser heterostructures under spontaneous-and stimulated-emission conditions

The charge-carrier concentration and the temperature of hot electrons and holes in quantum-well laser nanostructures in the regimes of spontaneous and stimulated emission are determined as functions of the current density j, with InGaAs/GaAs structures as an example. Under spontaneous-emission conditions, the carrier concentration in the active region of a laser structure grows as the current increases, while carrier heating is insignificant. The spontaneous-emission spectra calculated taking into account forbidden optical transitions agree well with the experimental ones. Under stimulated-emission conditions, the behavior is quite different. When the pump current density is comparatively low (several times above the threshold), the concentration of injected charge carriers levels off and does not grow as the current increases, while the carrier temperature rises considerably. When the current density exceeds the threshold value by orders of magnitude, stabilization of the charge-carrier concentration does not take place; the carrier concentration exhibits a severalfold increase and the carrier temperature rises to about 450 K at j = 80 kA/cm². The number of the charge carriers escaping from the quantum wells into the barriers, which determines the laser efficiency, also increases under these conditions because of the carrier heating. This undesirable effect can be weakened by increasing the depth of the quantum wells.     

超短脉冲激光烧蚀金属薄膜材料的热效应分析

基于双曲双温两步热传导模型,利用具有人工粘性和自适应步长的有限差分算法,对超短脉冲激光辐照金膜时的温度场进行了一维数值模拟计算.讨论了不同能量密度和脉冲宽度条件下金膜表面温度场的分布情况;分析了电子-晶格耦合系数对薄膜体内温度场的变化规律及电子-品格耦合至热平衡所需时间的影响.结果表明,激光脉冲的能量密度和脉冲宽度对电子温度的峰值有重大影响;电子-晶格的耦合系数决定了二者的温升速率和耦合时间;电子温度及电子温度的梯度在接近表面区域迅速达到最大值,与之相应的热电子崩力是造成金属薄膜早期力学损伤的主要原因.     

Gain-frequency-current relation for Pb1-xSnxTe double heterostructure lasers

The active region gain expression for Pb1-xSnxTe lasers is obtained from thek cdot pmodel of the conduction and valence band extrema. Curves of gain versus frequency with current, temperature, and majority carrier concentration as parameters are calculated using published values of thek cdot pmodel parameters. In addition, threshold current versus temperature and threshold current versus majority carrier concentration curves are given. A simple expression is obtained for the conductivity effective mass for use in the equation for free-carrier absorption appropriate to the highly degenerate majority carrier concentrations typical of Pb1-xSnxTe laser material.     

On the temperature delocalization of carriers in GaAs/AlGaAs/InGaAs quantum-well heterostructures

The effect of temperature delocalization in semiconductor lasers (emission wavelength λ = 1060 nm) based on symmetric and asymmetric separate-confinement heterostructures fabricated by metal-organic vapor-phase epitaxy (MOVPE) is studied. Experimental and calculated estimates show that the carrier concentration in the waveguide increases by an order of magnitude when the temperature of a semiconductor laser is raised by ～100°C. It is found that an increase in the temperature of the active zone leads to enhancement of the temperature delocalization of both electrons and holes. It is shown that the delocalization of holes begins at higher temperatures, compared with that of electrons. It is demonstrated experimentally that the onset of temperature delocalization depends on the threshold carrier concentration in the active region of a laser at room temperature. It is found that raising the energy depth of the active region by choosing the waveguide material makes it possible to fully suppress the temperature-delocalization process up to 175°C.     

脉冲激光辐照皮肤组织的热效应解析计算研究

具有一定强度的激光辐照皮肤组织时可造成组织的破坏.建立了激光与皮肤组织相互作用的二维非稳态温度场模型,在柱坐标系下采用积分变换法精确求解了单脉冲及多脉冲激光辐照皮肤组织的热传导方程,得到瞬态温度场分布,并以1064 nm波长激光辐照皮肤组织为例,数值模拟了皮肤组织在激光作用下的温度分布.研究结果表明:脉冲激光与组织的热效应在很大程度上取决于激光参数,主要有激光能量、焦斑半径、重复频率等.     

Measurement of Auger recombination in silicon by laser excitation

A new experimental arrangement for the study of Auger recombination in silicon is described and analyzed. A relatively weakly absorbed YAG:Nd laser beam was used for excitation. The decay of the carrier concentration after the injection pulse was studied by measuring the recombination radiation in a direction perpendicular to the laser beam. At some distance from the injection surface the influence of surface recombination and diffusion is then negligible. It has previously been shown that in this geometry the carrier concentration distribution after the laser excitation is accurately described by an analytical expression which accounts for attentuation of the laser beam by both interband and free carrier absorption. Thus the local carrier concentration in the sample can be computed to a high degree of accuracy, which is essential in the determination of the Auger recombination coefficient from decay measurements. Furthermore, this experimental geometry eliminates the problems with laser stray light. Assumptions regarding the influence of surface recombination and diffusion are not necessary in the interpretation of the experiments. The method is usable for silicon in the temperature interval 150–400 K. Preliminary measurements of the Auger coefficient at room temperature are reported.     

连续波激光辐照半导体InSb材料的熔融破坏

采用数值方法 ,研究了半导体 In Sb材料受连续波激光辐照的熔融阈值 ,讨论了 In Sb材料的熔融阈值与入射激光波长、功率密度以及辐照时间的关系 ,同时考虑了载流子效应对靶内温升过程以及熔融阈值的影响 ,给出了材料内温度与载流子密度的瞬态分布