共振声子太赫兹量子级联激光器研究

本文综述了共振声子太赫兹(THz)量子级联激光器(QCL)载流子输运及其光电特性的研究结果。我们采用Monte Carlo方法模拟了不同有源区结构的共振声子THz QCL,如四阱有源区和三阱有源区结构等,优化了THz QCL的器件参数。计算表明,器件的增益依赖于注入势垒的宽度、掺杂浓度和声子抽运能级间隔等参数。单阱注入的THz QCL可以获得低的激射频率,而三阱有源区结构的THz QCL具有更高的工作温度。我们数值模拟了这两种器件结构在不同寄生电压下的电子输运、增益以及温度特性等。同时,我们实验测量了THz QCL的发射谱偏压和温度效应,计算结果与实验相吻合。研究结果表明,随着偏压增加发射谱出现了明显的频率蓝移,多模激射仅出现在大电流注入情形。与偏压的密切依赖关系不同,激射频率对温度的变化并不敏感。     

太赫兹量子级联激光器材料生长及表征

采用气态源分子束外延方法生长了束缚态到连续态跃迁太赫兹量子级联激光器（terahertz quantum-cascade laser,简称THz QCL）有源区结构,并且采用电化学CV仪、霍尔测试仪以及高分辨X射线衍射对材料的质量进行表征,得出THz QCL有源区具有很高的晶体质量.另外,采用蒙特卡罗方法模拟了共振声子THz QCL器件的I-V曲线,分析了在不同偏压下子能级的对齐状况和电子的输运特征. 关键词： 太赫兹 量子级联激光器 分子束外延 X射线衍射     

基于太赫兹量子阱探测器的太赫兹量子级联激光器发射谱研究

采用一个光谱匹配的太赫兹(THz)量子阱探测器(QWP)研究了一激射频率约为41 THz的THz量子级联激光器(QCL)在不同驱动电流下的发射谱,分析了测量得到的发射谱谱型和谱峰位置,根据测量的发射谱估算了太赫兹量子级联激光器发射功率随驱动电流变化的情况,从而得到了THz QCL激射的电流密度范围及其阈值电流密度.文中还研究了THz QWP在不同温度下对THz QCL 激光辐射的响应特性.研究结果表明,THz QWP在表征THz QCL的发射谱方面是一种很好的探测器,并有望成为未来THz通信中的接收装置. 关键词： 太赫兹量子阱探测器 太赫兹量子级联激光器 太赫兹通信 Fourier变换红外光谱     

半绝缘等离子体波导太赫兹量子级联激光器工艺研究

采用气态源分子束外延设备生长了GaAs/AlGaAs束缚态到连续态跃迁结构的太赫兹（THz）量子级联激光器（QCL）有源区结构,研究了半绝缘等离子体波导THz QCL的器件工艺,采用远红外傅里叶变换光谱仪以及探测器测量了器件的电光特性.器件激射频率为32 THz,10 K下的阈值电流密度为275 A/cm². 关键词： 太赫兹 量子级联激光器 波导 器件工艺     

基于太赫兹量子阱探测器的太赫兹量子级联激光器发射谱研究

采用一个光谱匹配的太赫兹(THz)量子阱探测器(QWP)研究了一激射频率约为41 THz的THz量子级联激光器(QCL)在不同驱动电流下的发射谱,分析了测量得到的发射谱谱型和谱峰位置,根据测量的发射谱估算了太赫兹量子级联激光器发射功率随驱动电流变化的情况,从而得到了THz QCL激射的电流密度范围及其阈值电流密度.文中还研究了THz QWP在不同温度下对THz QCL 激光辐射的响应特性.研究结果表明,THz QWP在表征THz QCL的发射谱方面是一种很好的探测器,并有望成为未来THz通信中的接收装置.     

具有电子阻挡层的2 μm InGaAsSb/AIGaAsSb量子阱激光器

为了降低2 μm InGaAsSb/AlGaAsSb量子阱激光器的阈值电流并获得良好的温度特性,在p型波导层及限制层之间引入AlGaAsSb电子阻挡层.采用理论计算方法模拟了电子阻挡层对InGaAsSb/AlGaAsSb LD输出特性的影响.研究结果表明:电子阻挡层结构可有效减少2μm InGaAsSb/AlGaAsSb量子阱激光器的Auger复合,抑制量子阱中导带电子向p型限制层的溢出,降低器件的阈值电流,同时改善了温度敏感特性.     

低温808nm高效率半导体激光器

为了提高低温工作环境下808 nm半导体激光器的输出特性,深入研究了电光转换效率的温度特性。结合载流子泄漏抑制和器件串联电阻的优化考虑,从理论上深入分析了有源区量子阱内的载流子限制现象,提出针对低温工作环境下的势垒高度及相应的量子阱结构设计方法,包括势垒层的材料组分、厚度等重要参数的优化,极大地改善了器件在低温工作环境下的性能。采用优化后的外延结构,制备了腔长2 mm的半导体激光巴条。在工作温度-50℃、注入电流为600 A时,巴条输出功率达到799 W,电光转换效率为71%,斜率效率为1.34 W/A;注入电流为400 A时,器件达到最高电光转换效率73.5%,此时的载流子限制效率约为99%,串联电阻为0.43 mΩ;在-60～60℃温度范围内,中心波长随温度的漂移系数为0.248 nm/℃。     

分布反馈太赫兹量子级联激光器实现高功率单模输出

太赫兹量子级联激光器(THz QCL)是一种基于超晶格或耦合多量子阱中电子共振隧穿和子带间跃迁的单极光源,其辐射频率可通过能带和波函数设计进行调控,具有响应速度高、体积小、便于集成等优点。近年来,国际上多个科研团队展开了对THz QCL的密集研究,器件性能取得了显著的进展。针对THz QCL的实际应用,目前急切需要解决两个方面的问题:第一方面,受限于严重的大气衰减、光束合成等困难,急需解决THz QCL功率输出提升的问题。第二方面,研制窄线宽、高功率单模输出的太赫兹本振源。     

带间级联激光器电子注入区优化研究(特邀)

带间级联激光器有源区内部的物理机制复杂,尚未得到充分研究.优化了电子注入区结构,通过减小InAs/AlSb啁啾超晶格中InAs量子阱的厚度促进电子向光增益区的注入,在较低的电子注入区掺杂浓度下满足了光增益区电子数和空穴数基本相等的注入平衡条件,降低了有源区中自由载流子吸收和杂质散射造成的光损耗.采用该有源区结构的带间级...     

InP基高功率短波长量子级联激光器设计

阐述了InP基高功率短波长量子级联激光器(QCL)的设计原理和设计方案。从有源区设计模型出发,介绍了器件的理想和实际载流子传输路径,进而指出有源区设计的发展趋势和方法。根据器件的发展进程,综述了双声子共振设计,非共振抽取式设计,超强耦合设计,深阱设计,浅阱设计,短注入区设计等先进设计方案,这些设计方案使得QCL在低温下的电光转换效率在50%以上,最大室温连续输出功率超过3 W,而器件的特征温度T₀和T₁的最大值分别达到383 K和645 K。针对量子级联激光器的短波长高功率提供的先进设计方案扩大了QCL在民用与军用领域的应用前景,该设计方案亦可为其它波段量子级联激光器实现室温高功率的设计提供借鉴。     

Room‐temperature terahertz emission from ZnSe‐based quantum cascade structures: A simulation study

We identified conditions for room‐temperature operation of terahertz quantum cascade lasers (THz QCLs) where variable barrier heights are used on ZnSe/Zn_1–xMg_x Se material systems. The THz QCL devices are based on three‐level two‐well design schemes. The THz QCL lasers with alternating quantum barriers with different heights were compared with THz QCL laser structures with fixed quantum barrier heights. It is found that the THz QCL device with novel design employing variable barrier heights achieved the terahertz emission of about 1.45 THz at room‐temperature (300 K), and has improved laser performance due to the suppression of thermally activated carrier leakage via higher‐energy parasitic levels. Thus, THz QCL devices employing the design with variable barrier heights may lead to future improvements of the operating temperature and performance of THz QCL lasers. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Integrated injection seeded terahertz source and amplifier for time-domain spectroscopy

We used a terahertz (THz) quantum cascade laser (QCL) as an integrated injection seeded source and amplifier for THz time-domain spectroscopy. A THz input pulse is generated inside a QCL by illuminating the laser facet with a near-IR pulse from a femtosecond laser and amplified using gain switching. The THz output from the QCL is found to saturate upon increasing the amplitude of the THz input power, which indicates that the QCL is operating in an injection seeded regime.     

Terahertz Quantum Cascade Laser at 3.39THz

We demonstrate the growth of terahertz quantum cascade laser （THz QCL） by gas source molecular beam epitaxy. X-ray diffraction and cross-sectional transmission electron microscopic measurements show the high crystalline quality of the THz QCL active region, From the cross-sectional transmission electron microscopy image, sharp interfaces are observed and the deduced cascade period thickness is consistent with the result of x-ray diffraction. The test device is lasing at 3.39THz and operating up to lOOK in pulsed mode. At IOK, the maximum output power is greater than 1 mW with a threshold current density of 738 A/cm^2.     

2.9THz束缚态向连续态跃迁量子级联激光器研制

采用气源分子束外延技术生长了GaAs/AlGaAs束缚态向连续 态跃迁的太赫兹量子级联激光器材料, 基于半绝缘等离子体波导工艺制作了太赫兹量子级联激光器. 测量了激光器的发射光谱和功率-电流-电压关系曲线, 研究了器件的激光特性. 器件激射频率约2.95 THz, 脉冲模式下, 最高工作温度为67 K. 连续波模式下, 阈值电流密度最低为230 A/cm², 最大光输出功率1.2 mW, 最高工作温度为30 K. 关键词： 太赫兹 量子级联激光器 分子束外延 波导     

Performance optimization for terahertz quantum cascade laser at higher temperature using genetic algorithm

The aim of this work is to establish an approach for obtaining improved design parameters for high temperature operation of terahertz quantum cascade lasers using a multi-objective evolutionary algorithm. For studying the lasing conditions of a quantum cascade laser, a self-consistent model is adopted. This model uses standard wave function approximation and effective mass approximation with relevant scattering mechanisms to solve Schrodinger’s equation for the cascaded quantum wells. Fermi’s Golden Rule is then used to calculate the corresponding lifetime of each eigen states. To describe the coherent evolution of wave functions and phase breaking, density matrix formalism is employed. Subsequently, laser rate equations are used for calculating the parameters related to electronic transport in the device. These parameters are then utilized for investigating the temperature dependence of existing terahertz quantum cascade lasers. Finally, using an optimization technique based on Genetic algorithm, design parameters for resonant-phonon quantum cascade laser are obtained within the terahertz frequency range. The results illustrate that this optimization process can offer improvement in the performance of quantum cascade lasers in terahertz region at an elevated temperature. Moreover, the results also reveal that significant increase in operating temperature of a resonant phonon terahertz QCL is unlikely and hence novel design approaches should be considered for operating THz QCLs at room temperature.     

Terahertz dual-wavelength quantum cascade laser based on GaN active region

In this paper a novel terahertz (THz) quantum cascade laser (QCL) based on GaN/AlGaN quantum wells has been proposed, which emits at two widely separated wavelengths 33 and 52 μm simultaneously in a single active region. The large LO-phonon energy (～90 meV), the ultrafast resonant phonon depopulation of the lower radiative levels, suppression of the electrons that escape to the continuum states and selective carrier injection and extraction all together lead to a considerable enhancement in the operating temperature of the structure. All calculations have been done at a temperature of 265 K. Moreover, similar behavior of the output optical powers is another remarkable feature, which makes both wavelengths useful for special applications.     

Terahertz imaging through self-mixing in a quantum cascade laser

We demonstrate terahertz (THz) frequency imaging using a single quantum cascade laser (QCL) device for both generation and sensing of THz radiation. Detection is achieved by utilizing the effect of self-mixing in the THz QCL, and, specifically, by monitoring perturbations to the voltage across the QCL, induced by light reflected from an external object back into the laser cavity. Self-mixing imaging offers high sensitivity, a potentially fast response, and a simple, compact optical design, and we show that it can be used to obtain high-resolution reflection images of exemplar structures.     

Phase-locking of a 2.5 THz quantum cascade laser to a frequency comb using a GaAs photomixer

We report the heterodyne detection and phase locking of a 2.5?THz quantum cascade laser (QCL) using a terahertz frequency comb generated in a GaAs photomixer using a femtosecond fiber laser. With 10?mW emitted by the QCL, the phase-locked signal at the intermediate frequency yields 80?dB of signal-to-noise ratio in a bandwidth of 1?Hz.     

Frequency and phase-lock control of a 3 THz quantum cascade laser

We have locked the frequency of a 3 THz quantum cascade laser (QCL) to that of a far-infrared gas laser with a tunable microwave offset frequency. The locked QCL line shape is essentially Gaussian, with linewidths of 65 and 141 kHz at the -3 and -10 dB levels, respectively. The lock condition can be maintained indefinitely, without requiring temperature or bias current regulation of the QCL other than that provided by the lock error signal. The result demonstrates that a terahertz QCL can be frequency controlled with 1-part-in-10(8) accuracy, which is a factor of 100 better than that needed for a local oscillator in a heterodyne receiver for atmospheric and astronomic spectroscopy.