太赫兹量子级联激光器有源区有限元模拟

采用有限元分析法解决了太赫兹量子级联激光器(THz QCL)有源区模拟问题。由于InP基差频THz QCL有源区为千层纳米结构,无法拆分实验探索,因此模拟分析显得尤为必要。首先列出有源区量子结构的薛定谔方程,而后采用Galerkin有限元法改写薛定谔方程,再根据连续性和边界条件,得到本征值矩阵方程,最后采用Matlab写出运算程序求解本征值矩阵方程,求出波函数。针对不同有源区量子结构,设定材料、组分、厚度和周期数及外加偏压等参数,即可得到波函数模方、能级、频率和波长等模拟结果。选取InP基差频THz QCL结构进行验证,结果表明此模型切实可行,其拓展应用也可以解决GaAs THz QCL模拟问题。     

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.     

Optical Properties of Active Regions in Terahertz Quantum Cascade Lasers

In this work, AlGaAs/GaAs superlattice, with layers’ sequence and compositions imitating the active and injector regions of a quantum cascade laser designed for emission in the terahertz spectral range, was investigated. Three independent absorption-like optical spectroscopy techniques were employed in order to study the band structure of the minibands formed within the conduction band. Photoreflectance measurements provided information about interband transitions in the investigated system. Common transmission spectra revealed, in the target range of intraband transitions, mainly a number of lines associated with the phonon-related processes, including two-phonon absorption. In contrast, differential transmittance realized by means of Fourier-transform spectroscopy was utilized to probe the confined states of the conduction band. The obtained energy separation between the second and third confined electron levels, expected to be predominantly contributing to the lasing, was found to be ~9 meV. The optical spectroscopy measurements were supported by numerical calculations performed in the effective mass approximation and XRD measurements for layers’ width verification. The calculated energy spacings are in a good agreement with the experimental values.     

Low-Loss Surface-Mode Waveguides for Terahertz Si–SiGe Quantum Cascade Lasers

A new design of low-loss terahertz waveguide for Si-SiGe quantum-cascade lasers (QCLs) is presented. Periodic surface gratings are used to define waveguides without the requirement of cleaved or etched end facets. As Si cleaves along the (111) planes and not in the vertical direction for standard Si (100) substrates, this significantly aids the fabrication of waveguides. Losses down to 2 cm^-1 with modal overlap of 0.4 can be achieved for shallow gratings with etched depths of only 0.56 mum for an active material layer thickness of 8 mum. Such low loss and high modal overlap is key to any Si-SiGe QCL being realized     

共振声子THz QCL有源区结构设计

利用Airy函数代换与传输矩阵方法精确计算了有外加偏压下电子在共振声子太赫兹量子级联激光器有源区单个周期内的透射系数与波函数,得到了不同偏压下的电子波函数分布以及准束缚态能级位置与外加偏压的关系曲线.在仿真计算的基础上设计了一种共振声子太赫兹量子级联激光器的有源区结构.计算结果表明,对于设计的结构,当单个周期两端的外加...     

太赫兹量子级联激光器

太赫兹技术近年来发展迅速,应用越来越广泛,是当前的热门研究领域。太赫兹量子级联激光器是产生太赫兹辐射的重要器件,对太赫兹量子级联激光器的发展,以及有源区和波导层的设计等进行了详细讨论。     

Terahertz LC Microcavities: From Quantum Cascade Lasers to Ultrastrong Light-Matter Coupling

We review research on the physics of intersubband transitions in the THz range in a sub wavelength microcavity environment. Laser action was achieved at 1.5 THz by inserting quantum cascade gain material between the capacitor plates of a new resonant LC cavity, achieving a normalized mode volume ratio of only $V_{eff}/(\lambda /2n)^{3}=0.12$ of the cavity mode $V_{eff}$ and the normalized optical volume $(\lambda /2n)^{3}$ . By using the same cavity as the constituting meta-atom of a THz metamaterial, strong and ultra strong light matter coupling was observed up to room temperature. Finally, the same metamaterial coupled to parabolic semiconductor quantum wells was investigated in the regime of electrical in-plane pumping, showing THz emission in the ultra strong coupling regime.     

Voltage Tunability of Quantum Cascade Lasers

The voltage tunability of three types of quantum cascade laser designs is investigated. The tuning coefficients and tuning ranges of electroluminescence and laser emission from all designs are measured and compared with the calculated results. A reduced tunability was observed in all lasers above threshold. This is attributed to the decrease of resistance across the laser active region (AR) as the photon density increases. A resumed tunability high above threshold occurs in all lasers with anticrossed injector ground and upper laser states. Lasers based on the anticrossed diagonal transition are tunable above threshold, with a tuning range of about 30 ${hbox {cm}}^{-1}$ ($sim$ 3% of the laser emission wavenumber), i.e., a tuning rate of 750 ${hbox {cm}}^{-1} hbox{V}^{-1}cdot hbox{period}^{-1}$ of the AR and the injector.      

量子级联激光器的发展及其应用

量子级联激光器作为新近出现的全固化小型理想中远红外激光源,引起了人们极大的兴趣,本文介绍了量子级联激光器的发展、应用状况及一些可能的应用范围。     

Hot Electrons in THz Quantum Cascade Lasers

We compare the electrical power dependence of the lattice temperature and the electronic temperature of GaAs/Al_xGa_1-xAs THz quantum cascade lasers (QCLs) with different active region schemes, as extracted by the analysis of microprobe band-to-band photoluminescence experiments. Thermalized non-equilibrium distributions are found in all classes of QCLs. While in the case of bound-to-continuum structures all subbands share the same temperature, the upper laser level of active regions based on the resonant-phonon scheme heats up by ΔT ~ 100 K with respect to lower energy levels. The comparison among samples with different Al mole fractions show that the use of smaller x values leads to larger electronic temperatures.     

An Equivalent Circuit for Quantum Cascade Lasers

A new simpler equivalent circuit model of a quantum cascade laser based on two level rate equations is presented. The model is valid for small and large signals. A realistic current voltage model based on experimental results is included in the circuit model. Incorporation of the current voltage characteristic makes the circuit model fully compatible with parasitics and drive electronics. The model is validated by comparison of simulated results with analytica results and large signal numerical results reported earlier.     

中红外量子级联激光器的发射光谱测量

基于FTIR光谱仪建立了中红外半导体激光器发射光谱测量系统,并引入双调制技术改善了系统的性能。用此系统对中红外波段量子级联激光器的激射特性进行了测量,对有关测量结果进行了分析,并对系统应用中的有关问题进行了讨论。     

Optical Mode Control of Surface-Plasmon Quantum Cascade Lasers

Surface-plasmon waveguides based on metallic strips can provide a two-dimensional optical confinement. This concept has been successfully applied to midinfrared quantum cascade lasers, processed as ridge waveguides, to demonstrate that the lateral extension of the optical mode can be influenced solely by the width of the device top contact. In this configuration, the waveguide mode has a reduced interaction with the top metal and the ridge sidewalls. This results in lower propagation losses and higher performances. For devices operating at a wavelength of lambdaap7.5 mum, the room-temperature threshold current density was reduced from 6.3 to 4.4 kA/cm² with respect to larger devices with full top metallization     

Single Mode Operation of Short-Cavity Quantum Cascade Lasers

报道了激射波长为5.4和7.84μm的应变补偿In1-xGaxAs/In1-yAlyAs量子级联激光器的单模激射.以高质量的应变补偿量子级联激光器材料为支撑,通过减小FP腔长,开辟实现单模器件的新途径.首次实现阈值电流仅为50mA、腔长为145μm的激射波长在λ≈5.4μm的单模激射和阈值电流仅为80mA、腔长为170μm的激射波长在λ≈7.84μm的单模激射.这是目前InGaAs/InAlAs材料体系最短腔长的边发射量子级联激光器.     

High-Performance Growth of Terahertz Quantum Cascade Laser Structures by Solid Source MBE

Semiconductors - High performance growth of terahertz quantum cascade lasers (THz QCLs) based on hybrid bound-to-continuum transition and resonant phonon extraction is presented by solid source...     

Intersubband Absorption in Terahertz Lasers Based on Optically Pumped Quantum Well Structures

We study the effects of microscopic dynamics of electrons on the intersubband optical absorption in terahertz lasers based on optically pumped quantum wells (THz-OPQW). The ensemble Monte Carlo method is used to include different electron scattering mechanisms in the calculation, so that the dependence of intersubband absorption lineshape on microscopic dynamics of electrons can be easily investigated. We find that electron-electron scattering is the dominant factor to determine the absorption linewidth. The real distributions of hot electrons are included to study the temporal changes of the spectra lineshape. Our findings show that the dependence of spectral lineshape on electron population essentially results from the electron scattering and the non-Fermi electron energy distribution.     

基于发射光谱测量的中红外量子级联激光器热特性分析

基于不同脉冲工作条件下的激射光谱测量可以对激光器的一系列特性进行分析表征 ,为此建立了中红外激光器测量表征系统 ,其中包括引入双调制技术的 FTIR发射光谱测量系统和具有甚宽脉冲参数调节范围的 I-V、I-P测量系统 ,并通过计算机经由 GPIB总线进行控制 ,同时开发了相应的测量软件。利用此系统对采用气态源分子束外延技术生长的中红外波段 In Al As/In Ga As/In P量子级联激光器的热特性进行了测量分析 ,得出了器件的热阻参数 ,同时也对器件的激射温度范围、激射波长的温度特性、激射时的最高脉冲占空比、激射谱线宽度及其模式特征等一系列参数进行了测量 ,获得了有意义的结果。此测量系统在其他种类的中红外激光器测量上也有广泛用途     

On the Fabrication and Study of Lattice-Matched Heterostructures for Quantum Cascade Lasers

Semiconductors - The fabrication and study of the characteristics of a lattice-matched quantum cascade laser structure on an indium-phosphide substrate, designed for a wavelength of ~4.8 μm...     

共振声子太赫兹量子级联激光器研究

针对四阱有源区、一阱注入区及三阱有源设计,采用蒙特卡洛模拟方法研究了共振声子太赫兹量子级联激光器的性能差异。采用傅里叶变换光谱仪及远红外探测器测量了四阱共振声子太赫兹量子级联激光器的低温电光特性。详细讨论了提高太赫兹量子级联激光器发射功率的方案。