Photovoltaic spectroscopy of InGaAsP/InP multiple quantum wells

Photovoltaic Spectroscopy is used to study lattice matched Au/InGaAsP/InP multiple quantum wells at 4.2 < T < 300 K. Four quantum transitions are clearly identified in the spectra and their temperature shift mapped. The Au/InGaAsP Schottky barrier is found to be nearly temperature independent at φ_B ≃ 0.68 eV, and the binding energy of the 11H associated exciton estimated at E_b ≃ 11 meV. The 11H exciton displays a small electric field shift, to the red at low T, changing over to a blue shift at higher temperatures.     

Manganese-related luminescence in GaInAs/AlInAs multiple quantum wells grown on InP by molecular beam epitaxy

Two Mn-related luminescence peaks have been observed in a series of nominally undoped Ga_0.47In_0.53As/Al_0.48In_0.52As multiple quantum wells (MQW) grown lattice-matched on InP substrates by molecular beam epitaxy. These two peaks correspond to on-center and on-edge impurity states, respectively. The origin of the Mn impurities is outdiffusion from the Fe-doped semiinsulating InP substrate into the epitaxial layer. The binding energy of Mn acceptors, determined to be 53±3 meV in bulk-like Ga_0.47In_0.53As, increases to 80±5 meV for the on-center Mn state in a 58 Å MQW. The strong well-width dependence of the binding energy is explained in terms of the unique behavior of the Mn impurity in III–V semiconductors. The Mn in Ga_0.47In_0.53As and Ga_0.47In_0.53As/Al_0.48In_0.52As MQWs behaves predominantly as a deep impurity.On leave from: A. F. Ioffe Physicotechnical Institute, Leningrad, USSR     

离子注入诱导量子阱界面混合效应的光致荧光谱研究

采用多元芯片方法获得了一系列不同离子注入剂量的GaAsAlGaAs非对称耦合量子阱单元,通过光致荧光谱测量,研究了单纯的离子注入导致的界面混合效应.荧光光谱行为与有效质量理论计算研究表明,Al原子在异质结界面的扩散在离子注入过程中已基本完成,而热退火作用主要是去除无辐射复合中心. 关键词： 量子阱 离子注入 光致荧光谱 界面混合     

Advantages of InGaN/GaN multiple quantum well solar cells with stepped-thickness quantum wells

InGaN/GaN multiple quantum well (MQW) solar cells with stepped-thickness quantum wells (SQW) are designed and grown by metal-organic chemical vapor deposition. The stepped-thickness quantum wells structure, in which the well thickness becomes smaller and smaller along the growth direction, reveals better crystalline quality and better spectral overlap with the solar spectrum. Consequently, the short-circuit current density (Jsc) and conversion efficiency of the solar cell are enhanced by 27.12% and 56.41% compared with the conventional structure under illumination of AM1.5G (100 mW/cm2). In addition, approaches to further promote the performance of InGaN/GaN multiple quantum well solar cells are discussed and presented.     

Growth and characterization of strain-compensated InGaAs/GaAsSb type II multiple quantum wells on InP substrate

Strain-compensated InGaAs/GaAsSb type II multiple quantum wells (MQWs) were grown by molecular beam epitaxy (MBE) and their optical and electrical properties were studied. High-quality strain-compensated type II MQWs were successfully grown, which have longer emission wavelength than that of lattice-matched type II MQWs. PL peak energy at 300 K of the strain-compensated type II MQWs, where the InGaAs layer has 0.6% tensile strain and GaAsSb layer has 0.6% compressive strain, shows a red-shift of 43 meV, which is 12 meV larger than the calculated energy shift of 31 meV. In addition, the PL intensity and the electron mobility of the strain-compensated MQWs are comparable to those of the lattice-matched MQWs, suggesting that the crystal quality of the strain-compensated MQWs is good and are very promising for low dark current photodiodes in the 2 μm wavelength region.     

Erbium-doped fiber laser passively Q-switched by an InGaAs/InP multiple quantum well saturable absorber

We report on the behavior of an erbium-doped fiber laser passively Q-switched by an InGaAs/InP multiple quantum well semiconductor saturable absorber. The fiber is moderately doped in erbium ions. The saturable absorber consists of 40 periods of InGaAs (8.5 nm)/InP (10 nm) grown on an InP substrate. The laser efficiency is nonlinear under Q-switch regime and unusual temporal pulse shapes with rising times lower than decay times are observed around threshold. Pulse duration is around the microsecond range. Simple arguments based on a rate-equations approach are proposed in order to explain our results. They are justified a posteriori via numerical integration of the equations. The variation of threshold level versus spectroscopic parameters has been determined and that makes a guideline for generalizing our discussion.     

Fabrication of quantum wires by selective intermixing induced in GaAs/AlGaAs quantum well heterostructures by SiO2 capping and subsequent annealing

Results are presented demonstrating that selective intermixing of GaAs/AlGaAs quantum well heterostructures by SiO₂ capping and subsequent annealing can be spatially localized with a length scale compatible with the observation of lateral quantum confinement effects. Patterning of a 400 nm-thick SiO₂ encapsulation layer deposited by rapid thermal chemical vapor deposition into arrays of wires was performed using high resolution electron beam lithography and subsequent reactive ion etching. After high temperature (850°C) annealing, photoluminescence experiments indicate the creation of double barrier quantum wires when small trenches (< 100 nm) are etched in the SiO₂ film at a period greater than 800 nm. Signatures of the formation of one-dimensional subbands are observed both in photoluminescence excitation spectroscopy and linear polarization anisotropy analysis. A mechanism involving the ability of the stress field generated during annealing at the SiO₂ film edges to pilot the diffusion of the excess gallium vacancies which are responsible for the enhanced interdiffusion under SiO₂ is suggested to account for the high lateral selectivity achievable with this novel process.     

Crystallinity and interdiffusion in InP/InGaAs quantum wells grown by Hydride VPE

This paper reports the results of a study on interfacial quality and thermal interdiffusion for InP/InGaAs Quantum Wells (QW) grown by hydride VPE. By controlling well layer as thin as 25 Å, it was estimated that island and valley, whose height was one monolayer and whose lateral size was one third of exciton radius, existed at the interface. For the first time, interdiffusion coefficients for InP/InGaAs QW were obtained from 77K PL peak energy shift. Typical values were 2.5×10⁻¹⁹ cm²/sec and 1.5×10⁻¹⁸ cm²/sec for the annealing temperature of 700°C and 750°C, respectively. These values are over 10² times larger than that in AlGaAs/GaAs QW, and less 10⁻² times smaller than that in InAlAs/InGaAs QW.     

Computer simulation of the bombardment of a copper film on graphene with argon clusters

The process of graphene cleaning of a copper film by bombarding it with Ar_(13) clusters is investigated by the molecular dynamics method.The kinetic energies of the clusters are 5,10,20,and 30 eV and the incident angles are θ= 90°,75°,60°,45°,and 0°.It is obtained that the cluster energy should be in the interval 20 eV-30 eV for effective graphene cleaning.There is no cleaning effect at vertical incidence(θ =0°) of Ar_(13) clusters.The bombardments at 45° and 90° incident angles are the most effective on a moderate and large amount of deposited copper,respectively.     

Carrier transport and its effect on the turn-on delay time in strained GalnAsP/InP multiple quantum well lasers

The effects of carrier transport on turn-on delay time in multiple quantum well lasers were investigated both theoretically and experimentally. By using rate equation analysis with two components of the carrier density inside and outside of the quantum wells, we found that carrier transport caused two important effects: one is the stationary effect of a significant reduction in carrier density in quantum wells; the other is an increase in differential carrier lifetime.As an experimental investigation, compressively strained 1.3 m GalnAsP/InP multiple quantum well (MQW) lasers were fabricated and their turn-on delay times were measured and investigated. The short-cavity buried-heterostructure lasers showed low-threshold current (2 to 3 mA) and small turn-on delay time (<200 ps) at biasless 30 mA pulse current. Although these performances are suitable for high-speed digital transmission, it was found that the carrier lifetimes derived from the turn-on delay measurement were larger for strained quantum well lasers than for conventional quantum well lasers and double heterostructure lasers. These phenomena are explained using the carrier transport model and are discussed. The solutions for further reduction in carrier lifetime and turn-on delay are discussed.     

Temperature tuning of the Bragg resonance of InAsP/InP Bragg-spaced quantum wells grown by MOCVD

In this article, we presented a study of InAs_0.04P_0.96/InP Bragg-spaced quantum wells (BSQWs), which were grown by metal organic chemical vapor deposition (MOCVD). The quantum wells were characterized by photoluminescence (PL), double-crystal x-ray diffraction (DC-XRD), and reflection spectra. We found that the BSQWs structure grown at 580 °C appears to be extremely abrupt, uniform, free of misfit dislocations, and of narrow PL line width. From the reflection spectra at different temperatures, we presented a theoretical analysis of the changes in band structure for resonant and near-resonant wells, and proposed a new scheme of using the temperature to tune the Bragg resonance of Bragg spaced quantum wells.     

渐变掩蔽图形超低压选择区域生长法制备高质量InGaAsP多量子阱材料

采用超低压(22 mbar)选择区域生长(Selective Area Growth, SAG)金属有机化学汽相沉积(Metal-organic Chemical Vapor Deposition, MOCVD)技术成功制备了高质量InGaAsP/InGaAsP多量子阱(Multiple Quantum Well, MQW)材料. 在较小的掩蔽宽度变化范围内(15—30μm)，得到了46nm的光荧光(Photoluminescence, PL)波长偏移量，PL半高宽(Full-Width-at-Half- 关键词： 超低压 选择区域生长 渐变掩蔽图形     

Fabrication of an electro-absorption modulated distributed feedback laser by quantum well intermixing with etching ion-implantation buffer layer

We report the fabrication details of a monolithically integrated electro-absorption modulated distributed feedback laser(EML) based on the ion-implantation induced quantum well intermixing(QWI) technique.To well-preserve material quality in the laser region, thermal-oxide Si O2 is deposited before implantation and the ion-implantation buffer layer is etched before annealing. Thirteen pairs quantum well and barrier are employed to compensate deterioration of the modulator's extinction ratio(ER) caused by the QWI process.The fabricated EML exhibits an 18 d B static ER at 5 V reverse bias. The 3 d B small signal modulation bandwidth of modulator is over 13.5 GHz indicating that this EML is a suitable light source for over 16 Gb/s optical transmission links.     

Monolithic integration of electroabsorption modulators and tunnel injection distributed feedback lasers using quantum well intermixing

Electroabsorption modulators combining Franz-Keldysh effect and quantum confined Stark effect have been monolithically integrated with tunnel-injection quantum-well distributed feedback lasers using a quantum well intermixing method.Superior characteristics such as extinction ratio and temperature insensitivity have been demonstrated at wide temperature ranges.     

Growth of strain-compensated InGaAs/GaAsP multiple quantum wells by MOVPE

InGaAs/GaAsP strain-compensated multiple quantum wells (SCMQWs) and strained InGaAs/GaAsmultiple quantum wells (MQWs) were grown on GaAs substrates by metal organic vapor phase epitaxy(MOVPE). The results of double crystal X-ray diffraction (DCXRD) revealed that strain relief had beenpartly accommodated by the misfit dislocation formation in the strained MQW material. It led to thatthe full width half maximums (FWHMs) of superlattice satellite peaks are broader than those of SCMQWstructures, and there was no detectable room temperature photoluminecence(RT-PL)for the strained     

a-Si ∶H/SiO2多量子阱材料制备及其光学性能和微结构研究

利用等离子体增强化学气相沉积技术制备了a-Si ∶H/SiO₂多量子阱结构材料.对a-Si ∶H/SiO₂多量子阱样品分别进行了3种不同的热处理,其中样品经1100 ℃高温退火可获得尺寸可控的nc-Si:H/SiO₂量子点超晶格结构,其尺寸与非晶硅子层厚度相当.比较了a-Si ∶H/SiO₂多量子阱材料与相同制备工艺条件下a-Si ∶H材料的吸收系数,在紫外/可见短波段前者的吸收系数明显增大,光学吸收边蓝移,说明该材料 关键词： 多量子阱 量子限制效应 光学吸收 能带结构     

Second-harmonic spectroscopy of electronic structure of Si/SiO2 multiple quantum wells

Size effects in the resonant nonlinear optical response of amorphous Si/SiO₂ multiple quantum wells (MQW) are studied by second-harmonic generation (SHG) spectroscopy in a spectral interval of second-harmonic photon energies from 2.5 to 3.4 eV. The sensitivity of SHG spectroscopy to thickness-dependent electronic structure (sub-band energy position and density of states line shape) of MQW is demonstrated. A monotonic red shift of central energies of SHG resonances by 120 m eV upon increase of the well thickness from 2.5 to 10 ? is observed. This is interpreted as a size dependence of the position of singularities in the combined density of states for a 2D gas of electrons moving in an effective potential well. It is shown that, for agreement with experiment, the simplest (rectangular) shape of the well should be modified in order to take into account the lattice-potential distortion at the interfaces. Received: 16 October 2001 / Revised version: 16 April 2002 / Published online: 6 June 2002