Thermal Analysis of InAIAs／InGaAs／InP Mid——infrared QCLs Operating in CW Mode

A simulation method for the thermal analysis of InAlAs/InGaAs/InP mid--infrared quantum cascade lasers (QCLs) based on finite -- element method (FEM) is presented. The thermal distribution of the QCLs on substrate--side or epilayer--side mounting forms is simulated and the results are compared. Results show that the epilayer--side mounting form has much better heat dissipation capability than the substrate--side mounting.     

Improved CW operation of quantum cascade lasers with epitaxial-sideheat-sinking

First results on the epilayer-side mounting of quantum cascade (QC) lasers are presented. Operated in continuous-wave (CW) mode, these lasers are superior to substrate-bonded devices. The maximum CW temperature is raised by 20 K (up to 175 K), and, at comparable heat sink temperatures, the performance with respect to threshold current, output power, and slope efficiency is greatly improved for the epilayer-side mounted devices. QC-laser-specific mounting procedures are discussed in this letter, such as the high reflectivity coating of the back-facet and the front-facet cleaving after mounting. Modeling of the temperature distribution inside the QC laser shows a strong temperature gradient within the active waveguide core, which partly explains the still low maximum CW operating temperatures     

Thermal conductivity of ultra low-k dielectrics

The so-called 3ω measurement technique (transient hot wire method) was established to determine the thermal conductivity of thin films. Measurements of standard substrates and films validate the found thermal conductivity values and agree with published, commonly accepted values. The method was successfully applied to determine the thermal conductivity of porous low-k dielectric materials using special test structure fabrication. The thermal conductivity of the porous low-k dielectrics thus measured is only between 7 and 13% of the thermal conductivity of thermally grown silicon dioxide.     

Reliability analysis and design for the fine-pitch flip chip BGA packaging

The geometry of solder joints in the flip chip technologies is primarily determined by the associated solder volume and die/substrate-side pad size. In this study, the effect of these parameters on the solder joint reliability of a fine-pitched flip chip ball grid array (FCBGA) package is extensively investigated through finite element (FE) modeling and experimental testing. To facilitate thermal cycling (TC) testing, a simplified FCBGA test vehicle with a very high pin counts (i.e., 2499 FC solder joints) is designed and fabricated. By the vehicle, three different structural designs of flip chip solder joints, each of which consists of a different combination of these design parameters, are involved in the investigation. Furthermore, the associated FE models are constructed based on the predicted geometry of solder joints using a force-balanced analytical approach. By way of the predicted solder joint geometry, a simple design rule is created for readily and qualitatively assessing the reliability performance of solder joints during the initial design stage. The validity of the FE modeling is extensively demonstrated through typical accelerated thermal cycling (ATC) testing. To facilitate the testing, a daisy chain circuit is designed, and fabricated in the package for electrical resistance measurement. Finally, based on the validated FE modeling, parametric design of solder joint reliability is performed associated with a variety of die-side pad sizes. The results show that both the die/substrate-side pad size and underfill do play a significant role in solder joint reliability. The derived results demonstrate the applicability and validity of the proposed simple design rule. It is more surprising to find that the effect of the contact angle in flip chip solder joint reliability is less significant as compared to that of the standoff height when the underfill is included in the package.     

太赫兹Si/SiGe量子级联激光器波导模拟

波导层结构设计是制备太赫兹(THz)量子级联激光器的关键问题之一.本文基于德鲁得(Drude)模型,利用时域有限差分(FDTD)法,对Si/SiGe量子级联激光器的波导层进行优化设计,从理论上对传统的递变折射率波导、单面金属波导、双面金属波导以及金属/金属硅化物波导横磁模(TM模)的模式损耗和光场限制因子进行了对比分析.结果表明,金属/金属硅化物波导不但可以减小波导损耗,而且有很高的光学限制因子,同时其工艺也比双面金属波导容易实现,为Si/SiGe太赫兹量子级联激光器波导层的设计提供了一定的理论指导.     

中红外量子级联激光器的光子集成（特邀）

中红外光子集成芯片在环保监测、医疗诊断和国防安全等领域具有广泛的应用前景,但激光光源与无源波导光路的片上集成仍是中红外集成光学需要攻克的关键难题之一。量子级联激光器（QCL）是中红外波段的重要半导体激光光源,文中介绍了近几年中红外QCL在光子集成方面的研究进展,包括InP基单片集成、硅基单片集成、硅基异质键合集成和III-V/锗混合外腔激光器。     

太赫兹Si/SiGe量子级联激光器波导模拟

波导层结构设计是制备太赫兹(THz)量子级联激光器的关键问题之一.本文基于德鲁得(Drude)模型,利用时域有限差分(FDTD)法,对Si/SiGe量子级联激光器的波导层进行优化设计,从理论上对传统的递变折射率波导、单面金属波导、双面金属波导以及金属/金属硅化物波导横磁模(TM模)的模式损耗和光场限制因子进行了对比分析.结果表明,金属/金属硅化物波导不但可以减小波导损耗,而且有很高的光学限制因子,同时其工艺也比双面金属波导容易实现,为Si/SiGe太赫兹量子级联激光器波导层的设计提供了一定的理论指导.     

Al composition dependency of interface phonon in the wurtzite quantum cascade laser

The interface(IF) phonons of the wurtzite quantum cascade lasers(QCL) are investigated using the transfer-matrix method(TMM).The IF modes are presented in the longitudinal optical-phonon frequency for the Al0.2Ga0.8N/GaN and Al0.15Ga0.85N/GaN QCLs,and two IF modes can be changed into other modes if their wave numbers are less than the special values.Owing to the more dispersive properties of IF phonons with the increasing Al composition,the scattering rates in both QCLs increase with the Al composition.     

Thermal Modeling of Terahertz Quantum-Cascade Lasers: Comparison of Optical Waveguides

We compare a set of experimental lattice temperature profiles measured in a surface-emitting terahertz (THz) quantum-cascade laser (QCL) with the results of a 2-D anisotropic heat diffusion model. We evaluate the temperature dependence of the cross-plane thermal conductivity (kappa_perp) of the active region which is known to be strongly anisotropic due to its superlattice-like nature. Knowledge of kappa_perp and its temperature dependence is crucial in order to improve the temperature performance of THz QCLs and this has been used to investigate the longitudinal lattice temperature distribution of the active region and to compare the thermal properties of metal-metal and semi-insulating surface-plasmon THz optical waveguides using a 3-D anisotropic heat diffusion model.     

Resonant-phonon terahertz quantum-cascade laser operating at 2.1 THz (/spl lambda//spl sime/141 /spl mu/m)

The development of quantum-cascade lasers (QCLs) at 2.1 THz (/spl lambda//spl sime/141 /spl mu/m), which is the longest wavelength QCL to date without the assistance of magnetic fields, is reported. This laser uses a structure based on resonant-phonon depopulation, and a metal-metal waveguide to obtain high modal confinement with low waveguide losses. Lasing was observed up to a heatsink temperature of 72 K in pulsed mode and 40 K in continuous-wave (CW) mode, and 1.2 mW of power was obtained in CW mode at 17 K.     

宽谱太赫兹量子级联激光器的自混合特性

基于传输矩阵理论及多模速率方程,研究了宽谱太赫兹量子级联激光器在不同光反馈强度下的自混合动力学特性.研究发现,在弱反馈下光场自混合对激光器光谱特性影响很小;反射物位置移动时的自混合信号呈正弦规律变化,同时自混合信号幅度随反射物位置的变化表现出周期性调制现象.宽谱量子级联激光器在弱反馈下可以应用于测距、成像及光谱测量.在...     

Thermal fatigue in silicon power transistors

In silicon power transistor applications, thermal cycling of the transistor may activate a failure mechanism called thermal fatigue. This phenomenon is caused by the mechanical stresses set up by the differential in the thermal expansions of the various materials used in the assembly and heat sink of the transistor. Thermal fatigue often results in cracking of the silicon pellet or failure at the silicon mounting interface. This paper discusses the two types of interfaces encountered in power-transistor chip mounting. In type I (hard-solder) systems, the stress-strain relationship is treated in the elastic region. In type II (soft-solder) systems, the stress-strain relationship is plastic in that at least one component exhibits material flow. For the type I systems, a method is suggested for calculation of the forces acting at each interface. For type II systems, an empirical approach to predicting the number of cycles to failure is given. Accelerated testing techniques for thermal-fatigue evaluation are suggested, and a method of predicting performance for various mounting systems is given. This method uses an equation of the formN = A_{0}e^{(gamma0/H)}. This paper combines an analytical approach to the design of power transistors with an empirically derived method of predicting failure under conditions of thermal fatigue.     

Investigation of thermal effects in quantum-cascade lasers

The development of a thermal model for quantum cascade lasers (QCLs) is presented. The model is used in conjunction with a self-consistent scattering rate calculation of the electron dynamics of an InGaAs-AlAsSb QCL to calculate the temperature distribution throughout the device which can be a limiting factor for high temperature operation. The model is used to investigate the effects of various driving conditions and device geometries, such as epilayer down bonding and buried heterostructures, on the active region temperature. It is found that buried heterostructures have a factor of eight decrease in thermal time constants compared to standard ridge waveguide structures in pulsed mode and allow a /spl sim/78% increase in heat sink temperature compared to epilayer down mounted devices in continuous-wave mode. The model presented provides a valuable tool for understanding the thermal dynamics inside a quantum cascade laser and will help to improve their operating temperatures.     

The self-formation graded diffusion barrier of Zr/ZrN

In this paper, the 5 nm ZrN diffusion barrier was deposited by high vacuum magnetron sputtering method on Si substrate and the 300 nm Cu(Zr) alloy film or Cu film was sputtered on ZrN barrier without break vacuum. The self-formation graded Zr/ZrN diffusion barrier was obtained by annealing Cu(Zr)/ZrN bilayer system in N₂/H₂ (10% H₂) atmosphere. The X-ray diffraction (XRD) and four-point probe method were used to study graded Zr/ZrN diffusion barrier. The results revealed that the self-formation Zr barrier and ZrN barrier all obviously improved the thermal stability of Cu/Si system.     

太赫兹量子级联激光器及其光束表征技术

简要介绍太赫兹量子级联激光器(THz QCL)的工作原理及其进展。研究多个器件输出激光的光束质量,分别采用热探测器阵列和THz量子阱探测器(THz QWP)表征连续激射和脉冲激射THz QCL激光的光束图形,对比分析不同热探测器阵列对THz激光的表征能力,比较热探测器阵列和THz照相机对平行THz激光表征的差异。分析光束改善后THz激光光斑的尺寸、二维强度分布等特点,根据对THz QCL输出激光的改善效果,给出采用外部手段改善THz QCL激光光束的几种方法。研究表明,除了采用精细的波导工艺之外,锗(Ge)透镜、超半球高阻硅透镜和聚乙烯透镜都是外部改善技术中很好的手段。     

Measurements and modelling of thermal step current in GaN/SiO2/Si structure

In this work, we report results of measurement of space charge in GaN/SiO₂/Si structure by means of thermal step method (TSM) and capacitance-voltage (C-V). TSM is a non destructive method for quantifying and localizing the electric charges in insulating materials. Its principle consists to apply a low thermal step to a short-circuited or dc-biased sample and to record a current response, which depends on the charge present in the device. The C-V characteristics show an almost metal-oxide-semiconductor (MOS) behaviour and retention of charges after forward bias sweeping. The space charge dynamics in the structure are followed under low applied dc voltages. Results show a significant inversion of the TSM currents above applied voltage of 200 mV. A theoretical model is then presented in order to estimate the amount of the trapped charges and to interpret the variation of the TS currents as a function of the applied gate voltages.     

中远红外量子级联激光器研究进展(特邀)

量子级联激光器具有效率高、体积小、功耗低、波长可大范围选取的特点,已经被广泛应用于定向红外对抗系统、自由空间光通信和痕量气体传感等领域。回顾了量子级联激光器近20年的进展。首先总结了量子级联激光器的总体发展历程和发光原理;接着介绍了主要用于定向红外对抗的大功率量子级联激光器的几种典型有源区结构设计,然后讨论了气体传感用的单模分布反馈量子级联激光器;接着又论述了单片集成高亮度量子级联激光器相干阵列的研究情况;此外,还介绍了自由空间通信用的量子级联激光器的发展情况;最后,描述了近些年才出现中红外量子级联激光器光频梳的研究进展。     

Thermal Characteriztion of 1.3 μm InAsP／InGaAsP Ridge Waveguide MQW Laser Based on Spectroscopy Method

An experimental way to analyze the thermal characteriztion of semiconductor lasers based on spectroscopy method under pulse driving conditions has been developed,By using this way the thermal characteristicss of strain compensated 1.3 μm InAsP/InGaAsP ridge waveguide MQW laser diodes have been investigated.Results shovw that by measuring and analyzing the lasing spectra under appropriate driving parameters and temperature ranges,the thermal resistance of the laser diodes could be deduced easily,A higer thermal resistance of 640 K/W has been measured on a narrow ridge laser chip without soldering.Other thermal and spectral properties of the laser have also been measured and discussed.     

Thermal Characterization of 1.3μm InAsP/InGaAsP Ridge Waveguide MQW Lasers Based on Spectroscopy Method

An experimental way to analyze the thermal characterization of semiconductor lasers based on spectroscopy method under pulse driving conditions has been developed. By using this way the thermal characteristics of strain compensated 1.3μm InAsP/InGaAsP ridge waveguide MQW laser diodes have been investigated. Results show that by measuring and analyzing the lasing spectra under appropriate driving parameters and temperature ranges, the thermal resistance of the laser diodes could be deduced easily. A higher thermal resistance of 640K/W has been measured on a narrow ridge laser chip without soldering. Other thermal and spectral properties of the lasers have also been measured and discussed.     

High Resolution Terahertz Spectroscopy with Quantum Cascade Lasers

High resolution terahertz (THz) spectroscopy is a powerful analytical tool for laboratory purposes as well as for remote sensing in astronomy, planetary research, and Earth observation. THz quantum cascade lasers (QCLs) are promising sources for implementation into THz spectrometers, in particular at frequencies above 3 THz, which is the least explored portion of the THz region. One application of QCLs in THz spectroscopy is in absorption spectrometers, where they can replace less powerful and somewhat cumbersome sources based on frequency mixing with gas lasers. Another one is using a QCL as local oscillator in a heterodyne spectrometer for remote sensing. This article will review the state-of-the art in high resolution THz spectroscopy with QCLs.