Isolation spectra for InGaAs/GaAs strained single quantum well laser diode optical switches

The spectral dependence of gain and loss for an InGaAs/GaAs strained single quantum well laser diode were measured. High gain and high isolation at the second quantized transition wavelength can be obtained with a low injection current. A strained single quantum well structure is suitable for construction of an integrated optical matrix switch with low power consumption.     

超晶格中GaAs/InGaAs界面与InGaAs/GaAs界面的特性差异

In_xGa_1-xAs缓冲层上生长In_yGa_1-yAs/GaAs超晶格（x＜y）．阱层处于压缩应变，垒层处于伸张应变，其厚度均小于Mathews-Blakeslee（M-B）平衡理论计算的临界厚度．透射电子显微镜及俄歇电子能谱、二级离子质谱测试发现，GaAs/In_yGa_1-yAs界面铟组分过渡区比In_yGa_1-yAs/GaAs界面铟组 关键词：     

Cyclotron masses in InGaAs/GaAs superlattices and InGaAs/AlAs superlattices

Cyclotron resonance (CR) measurements have been carried out to evaluate the effective mass of electron in (InGaAs)_n/(GaAs)_nsuperlattices (SLs) and (InGaAs)_n/(AlAs)_nSLs. To clarify the dependence of cyclotron mass on the monolayer numbern , we measured CR signals using pulsed high-magnetic fields up to 150 T and a far-infrared laser. We found clear cyclotron resonances in the transmission of 10.6 μ m at 75 T at room temperature in (InGaAs)_n/(GaAs)_nSLs and little dependence on the monolayer number n in the SLs. However, for (InGaAs)_n/(AlAs)_nSLs, a large dependence of cyclotron mass on the monolayer number n was observed. We consider that these dependencies are related to the difference between the barrier height in the SLs and the influence of nonparabolicity on the conduction subbands in the SLs.     

Impurity cyclotron resonance in InGaAs/GaAs superlattice and InGaAs/AlAs superlattice grown on GaAs substrates

Various temperature measurements of cyclotron resonance (CR) under pulsed ultra-high magnetic field up to 160 T were carried out in InGaAs/GaAs superlattice (SL) and InGaAs/AlAs SL samples grown by molecular beam epitaxy on GaAs substrates. Clear free-electron CR and impurity CR signals were observed in transmission of CO₂ laser with wavelength of 10.6 μm. A binding energy of impurities in these SLs was roughly estimated based on the experiment as result, and we found it was smaller than the previous experimental result of GaAs/AlAs SLs and theoretical calculation with a simple model.     

High-gain and oscillatory transconductance by InGaAs/InAlAs multiple-quantum-well emitter bipolar transistor

We report an InGaAs/InAlAs multiple-quantum-well (MQW) emitter bipolar transistor prepared by molecular beam epitaxy. There are three distinct operating regimes to be observed in the studied structure. At small input base currents, low field band-type conduction provides the output current. The device exhibits a small gain and works as a normal transistor. With further increase in the base current, the high field starts appearing in the MQW superlattice. We observe that both the output current and transconductance exhibit an oscillatory behaviour in terms of sequential resonant-tunnelling through an expanding high field MQW domain. Beyond the condition of expansion of high field domain, the electron current increases rapidly by tunnelling through the triangular barrier and emitting over the base layer. The MQW superlattice now works as a barrier to hole minority carriers within this region. We obtain a common-emitter current gain as high as 240 with a small offset voltage of about 80 mV.     

Semiconductor waveguide optical switches and modulators

Semiconductor waveguide optical switches and modulators are reviewed from the view point of material and structure. As material for switches and modulators, effects of both variations of refractive index and absorption are considered. As for the structure of switches and modulators, basic characteristics of devices, including length, speed, and consumption power, are investigated, and recent experimental performances are shown. For further improvement of switches and modulators, the importance of low-dimensional quantum-well structures and strained quantum-well structures are pointed out.     

金辅助催化方法制备GaAs和GaAs/InGaAs纳米线结构的形貌表征及生长机理研究

利用金（Au）辅助催化的方法,通过金属有机化学气相沉积技术制备了GaAs纳米线及GaAs/InGaAs纳米线异质结构.通过对扫描电子显微镜（SEM）测试结果分析,发现温度会改变纳米线的生长机理,进而影响形貌特征.在GaAs纳米线的基础上制备了高质量的纳米线轴、径向异质结构,并对生长机理进行分析.SEM测试显示,GaAs/InGaAs异质结构呈现明显的“柱状”形貌与衬底垂直,InGaAs与GaAs段之间的界面清晰可见.通过X射线能谱对异质结样品进行了线分析,结果表明在GaAs/InGaAs轴向纳米线异质结构样品中,未发现明显的径向生长.从生长机理出发分析了在GaAs/InGaAs径向纳米线结构制备过程中伴随有少许轴向生长的现象.     

InGaAs/GaAs量子链的光学特性研究

研究了InGaAs/GaAs量子链的稳态和瞬态光谱特性,特别是载流子的动力学过程.实验发现荧光寿命有很强的探测能量依赖关系,荧光寿命随发光能量的增加而减小;实验还发现,当激发功率较小时,荧光寿命随激发功率增大而增大,当激发功率足够大时,荧光寿命趋于饱和.这些结果清楚地表明,在量子链结构中,参与发光的载流子之间存在明显的耦合和输运现象,进一步分析表明,这种输运主要是由于载流子沿量子链方向的耦合造成的.发光的偏振特性研究进一步证实了载流子沿量子链方向输运过程. 关键词： InGaAs/GaAs 量子点 量子链     

Asymmetric Fabry-Perot modulators with an InGaAs/AlGaAs active region

Strained layer superlattices have been used as the active region in asymmetric Fabry-Perot cavity optical modulators. The active layer of the Fabry-Perot modulator consisted of a 50 period In_0.15 Ga_0.85As/Al_0.30Ga_0.70As (10nm/10nm) superlattice. These quantum wells operate at typical wavelength of around 960 nm. By varying the length of the Fabry-Perot cavity in the modulator by including AlGaAs space layers of different thicknesses in the cavity, it is shown experimentally that both normally on and normally off devices can be obtained using the same stack of quantum wells. For the first type of device operation, a maximum contrast ratio of 8.3 dB could be measured for a reverse voltage of 7 V at 969 nm, while for the second type, a maximum of 8.9 dB at 957 nm was obtained for a 20 V reverse voltage. Using the same structure with an extra Bragg reflector on top of the quantum well layers to increase the surface reflection, a device with a higher finesse of the cavity was obtained. A maximum contrast ratio of 11.5 dB was measured for a reverse bias voltage of 30 V at 978 nm, with an insertion loss of –4.2dB.     

Lock-in holography using optically addressed multiple-quantum-well spatial light modulators

Perpendicular-field multiple-quantum-well optically addressed spatial light modulators have a response that saturates at high writing intensity. This limits the diffraction efficiency of low-fringe-visibility holograms. This effect is suppressed by use of the ability of these structures to subtract images rapidly. The modulator is exposed to a hologram with a spatially uniform beam, which is incoherent with the hologram, superimposed on top of it. Pulsing the hologram synchronously with the device drive voltage but leaving the uniform beam constant in time can build up the diffraction to large values even when the fringe visibility is low.     

Lateral and vertical ordered one-dimensional InGaAs/GaAs quantum structures

Lateral and vertical ordered one-dimensional quantum structures, i.e. InGaAs/GaAs(001) quantum dot chains and quantum wires, have been obtained using molecular beam epitaxy. It was found that the InGaAs wires or dot chains sit on two-dimensional wetting layers and run along the [-110] direction, as the result of anisotropic strain and in-plane adatom diffusion. This anisotropic nature produces a model system for studying the electronic properties of one-, two-, and three-dimensional quantum confinements and related optical responses. The strain anisotropy is of importance in determining the electronic states of the quantum structures and the surrounding strained barrier. The strain-induced effects, such as change of band-gap and splitting of heavy–light hole states, were studied experimentally and theoretically. Optical anisotropy of these quantum structures is also discussed.     

Numerical study on InGaAsN/GaAs multiple-quantum-well laser with GaAsP and GaAsN barriers

In this work, the multiple-quantum-well InGaAsN laser structures with indirect-GaAsP and direct-GaAsN barriers are investigated by using LASTIP simulation program. We vary the quantum-well number, from 1 to 5, to find appropriate barrier material for InGaAsN laser structures. The simulation results show that InGaAsN laser structure has higher characteristic temperature regardless of what quantum-well number is if the indirect-GaAsP barrier is utilized. Furthermore, for InGaAsN laser structure, the usage of indirect-GaAsP barrier is beneficial for reducing the threshold current when the quantum-well number is from 1 to 2 and the usage of direct-GaAsN barrier is beneficial for reducing the threshold current when the quantum-well number is from 3 to 5.     

Electron spin beats in InGaAs/GaAs quantum dots

Time-resolved picosecond spectroscopy is used for the first time to study optical orientation and spin dynamics of carriers in self-organized In(Ga)As/GaAs quantum-dot (QD) arrays. Optical orientation of carriers created by 1.2 ps light pulses, both in the GaAs matrix and wetting layer, and captured by QDs is found to last a few hundreds of picosecond. The saturation of electron ground state at high-excitation-light intensity leads to electron polarization in excited states close to 100% and to its vanishing in ground state. Electron-spin quantum beats in a transverse magnetic field are observed for the first time in semiconductor QDs. We thus determine the quasi-zero-dimensional electron g factor in In_0.5Ga_0.5As/GaAs QDs to be: |g _⊥|=0.27±0.03. Fiz. Tverd. Tela (St. Petersburg) 41, 871–874 (May 1999) Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor.     

InGaAs/GaAs应变量子阱的光谱研究

分别用光致发光谱（PL），光伏谱（PV）及时间分辨谱（TRPL）的方法，测量了应变InGaAs/GaAs单量子阱和多量子阱在不同温度下的光谱，发现单量子阱与多量子阱有不同的光学4性质。多量子阱PL谱发光峰和PV谱激子峰的强度与半高宽都比单量子阱的大，但单量子阱的半高宽随着温度的升高增大很快，这是由激子－声子耦合引起的，通过时间分辨谱研究发现了量子阱子能级之间的跃迁，多量子阱的发光寿命明显比单量子阱的长，我们利用形变势模型对量子阱的能带进行了计算，很好地解释了实验结果。     

Photoluminescence saturation in InGaAs/GaAs single quantum wells

Saturation of the photoluminescence associated with the 11H transition in the InGaAs single quantum wells is observed under high intensity optical excitation. At the onset of saturation, a spill-over of the photoluminescence occurs into the GaAs cladding layers as the excitation intensity is increased. The measurements are used to determine a limiting value of the quantum efficiency of the quantum-well associated photoluminescence.     

Selective polarization mode excitation in InGaAs/GaAs microtubes

We report on selective polarization mode excitation in InGaAs/GaAs rolled-up microtubes. The microtubes are fabricated by selectively releasing a coherently strained InGaAs/GaAs quantum dot layer from its host GaAs substrate. An optical fiber abrupt taper is used to pick up the microtube, while an adiabatically tapered optical fiber is used to couple light into the resonant optical modes of the microtube. By varying the polarization of the light in the adiabatically tapered fiber both transverse electric and transverse magnetic modes are observed in the microtube. We also show that the microtube can be used as a red (0.6?μm) to infrared light (1.5?μm) optical-optical modulator taking advantage of the thermal-optical effect.     

亚单层InGaAs量子点-量子阱异质结构的时间分辨光致发光谱

测定了亚单层InGaAs/GaAs量子点-量子阱异质结构在5K下的时间分辨光致发光谱.亚单层量 子点的辐射寿命在500 ps 至 800 ps之间，随量子点尺寸的增大而增大，与量子点中激子的 较小的横向限制能以及激子从小量子点向大量子点的隧穿转移有关.光致发光上升时间强烈 依赖于激发强度密度.在弱激发强度密度下，上升时间为 35 ps，纵光学声子发射为主要的 载流子俘获机理.在强激发强度密度下，上升时间随激发强度密度的增加而减小，俄歇过程 为主要的载流子俘获机理.该结果对理解亚单层量子点器件的工作特性非常有用. 关键词： 亚单层 量子点-量子阱 时间分辨光致发光谱     

Partial intermixing of strained InGaAs/GaAs quantum wells

Shallow ion implantation and rapid thermal annealing (RTA) was used to modify the optical properties of strained InGaAs/GaAs quantum wells (QWs). After RTA, QW exciton energies, determined from peak positions of the photoluminescence spectra, shifted significantly to higher energies in the implanted areas, whereas they remained basically unaffected in the unimplanted regions. The magnitudes of the energy shifts depend on the well width, RTA temperature and ion implantation fluence. The shifts were interpreted as arising from modification of the shapes of the as-grown QWs due to diffusion of In out of the well material. This process is enhanced by diffusion of vacancies generated near the sample surface by ion implantation. QWs with compositions near the critical thickness exhibit different behaviour from that of fully pseudomorphic layers, due to the presence of dislocations in these layers.     

High-strain InGaAs/GaAs quantum well grown by MOCVD

High-strain InGaAs/GaAs quantum wells （QWs） are grown by low-pressure metal-organic chemical vapor deposition （LP-MOCVD）. Photoluminescence （PL） at room temperature is applied for evaluation of the optical property. The influence of growth temperature, V/III ratio, and growth rate on PL characteristic are investigated. It is found that the growth temperature and V/III ratio have strong effects on the peak wavelength and PL intensity. The full-width at half-maximum （FWHM） of PL peak increases with higher growth rate of InGaAs layer. The FWHM of the PL peak located at 1039 nm is 20.1 meV, which grows at 600 ℃ with V/ III ratio of 42.7 and growth rate of 0.96 μm/h.