半导体GaAs—Ga0.65Al0.35As多量子阱的光谱性质及实现激光制冷的可能

我们利用光致发光(PL)和激发光谱(PLE)技术研究了GaAs量子阱的光谱性质,在GaAs量子阱的光致发光中观察到上转换发光,首次提出GaAs量子阱结构可能实现激光制冷,探索了GaAs量子阱结构的发光机理。     

半导体GaAs—Ga0.65Al0.35As多量子阱的光谱性质及实现激光制冷的可能

我们利用光致发光（PL）和激发光谱（PLE）技术研究了GaAs量子阱的光谱性质,在GaAs量子阱的光致发光中观察到上转换发光,首闪提出GaAs量子阱结构可能实现激光制冷,探索了GaAs量子阱结构的发光机理。     

MOCVD生长GaAsP/InGa(Al)P/GaAs大功率808nm张应变量子阱激光器材料

设计了808 nm高功率GaAsP/InGaAlP/GaAs半导体激光器,采用无铝张应变量子阱和非对称宽波导结构,通过优化金属有机物气相沉积(LP-MOCVD)生长条件,提高了外延材料的生长质量,有效提升了激光器转化效率和输出功率。制作了200μm条宽、1500μm腔长的激光器器件,室温连续条件(CW)测试其阈值电流为650 mA,斜率效率高达到1.35 W/A,输出功率在11 W以上,激射波长808.5 nm@5A,水平和垂直发散角分别为8°和30°,较小的发散角有效的提高了输出光功率密度。     

GaN基蓝绿光激光器发展现状与未来发展趋势

氮化镓(GaN)基蓝光和绿光激光器在投影显示、激光加工、激光照明、存储等领域具有重要的应用前景与广泛的市场需求.本文着重介绍了GaN基蓝光和绿光边发射激光器的技术难点和相应的解决方案.在GaN基蓝光与绿光激光器中,就制备高质量InGaN/GaN多量子阱、减少内部光学损耗、增加空穴注入效率等方面分别介绍了一些结构与工艺方面的优化方法.简要介绍了垂直腔面发射激光器(VCSEL)、分布式反馈激光器(DFB)的研究现状.     

AlGaN量子结构及其紫外光源应用

AlGaN量子结构是实现高光效、高稳定紫外固态光源的核心.近年来,AlGaN半导体材料及其紫外光源应用研究取得了较大的进展.然而,AlGaN材料的生长制备只能在非平衡条件下完成,涉及的生长动力学问题十分复杂,制约了量子阱等结构品质的提高;材料带隙宽,p型掺杂难度大,激活效率低,限制了载流子注入;光学各向异性显著,不利于光从器件正面出射.因此,AlGaN基紫外、特别是深紫外波段器件性能还有待提高.本文梳理了AlGaN量子结构与紫外光源效率之间的关系,详细阐述和总结了有源区量子结构、p型掺杂量子结构以及光学各向异性调控等方面所面临的挑战及近年来的重要研究进展.     

量子点激光器和量子点能态的计算

本文首先从态密度的角度,分析了半导体激光器从三维到零维发展的内因;介绍了实现量子点的工艺和量子点激光器的研究进程;评述了影响量子点激光器发展的"瓶颈"问题.在文章的后半部分,介绍了量子点电子态的计算,其中着重介绍了k·p微扰法.     

基于AlInGaAsP材料的应变平衡量子阱太阳能电池

近年来,基于晶格匹配的多结太阳能电池光电转换效率已经接近30;[1,2],中国电子科技集团公司第十八研究所三结GaInP/GaAs/Ge电池技术已经达到小批量生产水平.为了进一步提高多结太阳电池的转换效率,可以采用增加pn结的数量和优化三结电池子电池带宽组合等办法,但上述途径受到材料晶格匹配的限制,目前同时实现晶格匹配和最佳带宽的材料生长还存在一些问题.为此,我们采用与多结电池技术兼容的设备和材料,开展了基于AlInGaAsP材料的应变平衡量子阱太阳能电池的研究.本文给出GaAs单结量子阱电池的实验过程及结果,证实了量子阱结构的引入确实能够提高电池的输出电流.随着研究的深入,我们希望用此结构作为中间电池,以提高三结电池的效率.     

MOCVD生长低阈值电流GaInP/AlGaInP650nm激光器

通过MOCVD外延实现了限制层高铝组分及高掺杂,制作出低阈值电流密度的压应变多量子阱激光器材料,后工艺制备了低阈值电流基横模弱折射率脊形波导激光器.该激光器阈值电流最低达到6.2mA,这是我们所见报道的650nm AlGaInP红光激光器的最低阈值电流. 在25mA 工作电流下,基横模连续输出功率达到18mW.     

Mg掺杂AlInP限制层窗口结构高功率(3.7 W) 660 nm AlGaInP宽面半导体激光器

本文采用低压金属有机化学气相沉积系统(LP-MOCVD)生长出Mg掺杂压应变分别限制多量子阱结构的AlGaInP/GaInP 660 nm LD外延材料,制作出腔长1000 μm、条宽150 μm的宽面半导体激光器.采用选择性Zn扩散在管芯两端面区制作出透明窗口结构来提高器件的腔面光灾变阈值(COD).透明窗口结构激光器最大连续输出功率为3.7 W,是正常结构的激光器COD饱和功率的4.4倍.激光器的特征温度T0为68 K,热阻为4.6 K/W.在热沉温度为20 ℃时进行了500 mW恒功率老化,老化时间为1000 h.     

Yb:CaGdAlO4晶体及其超快激光技术研究进展

Yb∶CaGdAlO₄(简写为Yb∶CALGO)晶体具有部分无序的结构、优秀的热学和光谱性质、吸收发射带宽，适合采用商用高功率InGaAs二极管泵浦以实现高功率超快激光运转，其较高的非线性折射率系数有利于对锁模激光器的优化。该晶体还具有能级结构简单、本征量子缺陷低、辐射量子效率高等优点，是近年来新一代紧凑型、高效率、低成本激光二极管(LD)泵浦飞秒激光增益介质。本文简要介绍Yb∶CALGO的晶体结构、晶体生长、缺陷分析、热学性质和光谱性质等，并综合国内外学者近期的一些研究成果，重点综述了Yb∶CALGO晶体在半导体可饱和吸收镜、克尔透镜锁模的超快激光器及再生放大器超快激光技术中的最新研究进展。     

Microscopic modeling of the optical properties of semiconductor nanostructures

A brief overview of a consistent microscopic approach to model the optical and electronic properties of semiconductor nanostructures is presented. Coupled semiconductor Bloch and Maxwell equations are used to investigate the performance of semiconductor microcavity structures, photonic band gap systems, and lasers. The predictive potential of the microscopic theory is demonstrated for several examples of practical importance. Optical gain and output characteristics are computed for modern vertical external cavity surface emitting laser structures. It is shown how design flexibilities can be used to optimize the device performance. Nanostructures are proposed where semiconductor quantum wells are embedded in one-dimensional photonic crystals. For field modes spectrally below the photonic band edge it is shown that the optical gain and absorption can be enhanced by more than one order of magnitude over the value of the homogeneous medium. The increased gain can be used for laser action by placing quantum wells and a suitably designed photonic crystal structure inside a microcavity.     

高功率激光与“超热导”激光晶体

高功率固体激光技术的发展史就是一部与“废热”的斗争史,为抑制热效应对光束质量的不利影响,先后出现了热容激光器、薄片激光器、板条激光器以及光纤激光器,新的增益介质形态结合先进的散热技术将激光输出功率提升至百千瓦量级。固体激光增益介质的热学性能是限制激光功率进一步取得突破的重要瓶颈。因此,寻找具备超高热导率的激光晶体材料意义重大。本文介绍了上述四种激光器的基本原理及其在高功率激光方面取得的研究进展,从提高增益介质材料热导率的角度出发,对目前已有的方法和研究成果进行了分析与总结,对超热导激光晶体研究和高功率激光技术的发展进行了展望。     

GaAs/AlGaAs quantum wire lasers fabricated by cleaved edge overgrowth

We have used the molecular beam growth technique which we call "cleaved edge overgrowth" to fabricate quantum wire lasers, in which 1D quantum confinement is entirely defined by the growth process. The active region of our lasers consists of atomically precise quantum wires that form at the T-shaped intersections of 7 nm wide GaAs quantum wells grown along the [001] crystal axis and after an in situ cleave along the [110] crystal axis. The origin of the quantum mechanical bound state is the relaxation of quantum well confinement at this intersection. The high degree of structural perfection achievable in this way allows the observation of stimulated optical emission from the lowest exciton state in optically as well as in electrically pumped devices. The formation of a linear p-n junction in which the quantum wires are embedded is achieved by doping with Be and Si in the two orthogonal growth directions. Efficient current injection into the wires is demonstrated by the almost complete suppression of optical emission from the quantum well states as well as by threshold currents as low as 0.4 mA for uncoated devices at 1.7 K.     

Growth of strain-compensated GaInNAs/GaAsP quantum wells for 1.3 μm lasers

Strain-compensated GaInNAs/GaAsP quantum well structures and lasers were grown by gas source molecular beam epitaxy using a RF-plasma nitrogen radical beam source. The optimal growth condition for the quantum well structure was determined based on room-temperature photoluminescence measurements. Effects of rapid thermal annealing (RTA) on the optical properties of GaInNAs/GaAsP quantum well structures as well as laser diodes are examined. It was found to significantly increase the photoluminescence from the quantum wells and reduce the threshold current density of the lasers, due to a removal of N induced nonradiative centers from GaInNAs wells.     

Growing of bulk crystals and structuring waveguides of fluoride materials for laser applications

We report on recent progress in the synthesis, the crystal growth and the epitaxial growth of fluoride and other laser materials. Results on the fabrication of single crystalline waveguides for dielectric down - and upconversion lasers pumped by semiconductor diode lasers are summarized. Epitaxial growth (molecular beam epitaxy (MBE), liquid phase epitaxy (LPE), pulsed laser deposition (PLD)) and surface modifying techniques (high energy ion implantation, ion diffusion) have been applied in several laboratories. Progress in techniques fabricating optical waveguides from glassy media is addressed as well. Particular emphasis is given on the structuring (wet etching, chemical polishing, ion beam etching) of fluoride crystals for the purpose of obtaining 2-D and 1-D optical waveguides. Results on the structuring of LiYF₄ by wet and ion beam etching are reported. With respect to laser action, the generation of short wavelength light by upconversion (UC) processes, stimulated Raman scattering (SRS) and second harmonic generation (SHG) is discussed. Reports on the first crystalline waveguide lasers of fluoride crystals LiYF₄ and LaF₃, both doped with neodymium, are presented.     

无序激光晶体及其超快激光研究进展

激光是受激辐射的光放大,所辐射的波长取决于增益介质中关键电子的能级结构,特别是其最外层电子的状态决定了可能实现的激光特性。激光发展60年来,激光晶体作为激光的重要激活材料,推动了激光技术的进步和普及,是一个研究历史长而又异常活跃的研究领域。当前,超短超强脉冲激光在加工、医疗、国防等关系国计民生的领域有重要需求,适合超短超强激光的激光晶体成为了本领域的研究热点,其关键是揭示最外层电子的影响因素及设计和生长具有宽波段发射性能的激光晶体。本论文从探讨影响激活离子光谱性能的关键因素出发,综述了以本课题组十余年研究的10余种无序激光晶体为主要部分的研究结果和进展,涉及晶体生长、晶体物理、激光器件设计及应用等工作,包含了高级、中级和低级对称性晶体及其获得的最短脉冲激光结果,希望能为本领域的后续研究提供一定的参考和借鉴。     

Double heterostructure lasers prepared by LPE on medium-quality GaAs substrates under controlled as vapour conditions

The fact that defect formation in (Ga, Al)As LPE layers can be suppressed by the presence of arsenic vapour is employed to improve properties of double heterostructure (DH) lasers. The controlled vapour pressure (CVP) method is implemented using a modified LPE horizontal carbon boat. Growth kinetics study under near-equilibrium conditions shows that the presence of arsenic vapour diminishes the growth rate of aluminium-containing layers; no such influence has been observed with the GaAs layers. The CVP method, compared with the customary LPE, has a beneficial effect on the DH surface and cross sections perfection, as well as on the lasing characteristics (differential quantum efficiency, threshold current). Observed values of the parameter T₀, characterizing temperature dependence of the laser threshold current, fall into the vicinty of 200 K. The results have been obtained on medium-quality GaAs substrates.     

CBE growth of low threshold 1.5 μm InGaAs/InGaAsP MQW lasers

This paper reports on low-threshold InGaAs/InGaAsP multiple quantum well (MQW) lasers emitting at a wavelength of 1.52 μm. Separate confinement heterostructure (SCH) lasers were grown using chemical beam epitaxy (CBE) with source material pressure-control systems. A continuous wave threshold current of 12 mA and internal quantum efficiency of 73% (both facets) are observed in uncoated double-channel planar buried heterostructure (DCPBH) lasers. The internal loss is 15 cm^-1. More than 90% of 50 laser chips have a threshold current of 15±3 mA.     

Metamorphic InAs(Sb)/InGaAs/InAlAs nanoheterostructures grown on GaAs for efficient mid-IR emitters

High-efficiency semiconductor lasers and light-emitting diodes operating in the 3–5?μm mid-infrared (mid-IR) spectral range are currently of great demand for a wide variety of applications, in particular, gas sensing, noninvasive medical tests, IR spectroscopy etc. III-V compounds with a lattice constant of about 6.1?Å are traditionally used for this spectral range. The attractive idea to fabricate such emitters on GaAs substrates by using In(Ga,Al)As compounds is restricted by either the minimum operating wavelength of ～8?μm in case of pseudomorphic AlGaAs-based quantum cascade lasers or requires utilization of thick metamorphic In_xAl_1-xAs buffer layers (MBLs) playing a key role in reducing the density of threading dislocations (TDs) in an active region, which otherwise result in a strong decay of the quantum efficiency of such mid-IR emitters. In this review we present the results of careful investigations of employing the convex-graded In_xAl_1-xAs MBLs for fabrication by molecular beam epitaxy on GaAs (001) substrates of In(Ga,Al)As heterostructures with a combined type-II/type-I InSb/InAs/InGaAs quantum well (QW) for efficient mid-IR emitters (3–3.6?μm). The issues of strain relaxation, elastic stress balance, efficiency of radiative and non-radiative recombination at T?=?10–300?K are discussed in relation to molecular beam epitaxy (MBE) growth conditions and designs of the structures. A wide complex of techniques including in-situ reflection high-energy electron diffraction, atomic force microscopy (AFM), scanning and transmission electron microscopies, X-ray diffractometry, reciprocal space mapping, selective area electron diffraction, as well as photoluminescence (PL) and Fourier-transformed infrared spectroscopy was used to study in detail structural and optical properties of the metamorphic QW structures. Optimization of the growth conditions (the substrate temperature, the As₄/III ratio) and elastic strain profiles governed by variation of an inverse step in the In content profile between the MBL and the InAlAs virtual substrate results in decrease in the TD density (down to 3?×?10⁷ cm^?2), increase of the thickness of the low-TD-density near-surface MBL region to 250–300?nm, the extremely low surface roughness with the RMS value of 1.6–2.4?nm, measured by AFM, as well as rather high 3.5?μm-PL intensity at temperatures up to 300?K in such structures. The obtained results indicate that the metamorphic InSb/In(Ga,Al)As QW heterostructures of proper design, grown under the optimum MBE conditions, are very promising for fabricating the efficient mid-IR emitters on a GaAs platform.