Confinement Layer Research Articles

Theory of operating characteristics of a semiconductor quantum well laser: Inclusion of global electroneutrality in the structure

A model for calculating the operating characteristics of semiconductor quantum well (QW) lasers is presented. The model exploits the condition of global electroneutrality, which includes the charge carriers both in the two-dimensional (2D) active region (QW) and bulk waveguide region (optical confinement layer - OCL). The charge of each sign in the OCL is shown to be significantly larger than that in the QW. As a result of this, (i) the global electroneutrality condition reduces to the condition of electroneutrality in the OCL and (ii) the local electroneutrality in the QW can be strongly violated, i.e., the 2D electron and hole densities in the QW can significantly differ from each other.

Surface Modification of Red Brass Alloy by Using Laser Technique

Laser shock processing technique was performed on red brass alloy type C83300 specimens for the purpose ofstudy its effect on the mechanical properties such as micro-hardness and surface roughness. LSP experimental setup system involved Q-switched Nd:YaG laser of wavelength of 1064nm and 10 ns laser pulse . Double distilled deionized water (DDDW) is used as the transparent confining layer. The effects of the LSP parameters as laser pulse energy, number of laser pulses and thickness of confinement layer on the surface micro-hardness, and surface roughness were investigated. The experimental results show that, the surface roughness and micro-hardness values increased when the laser parameters (mentioned above) have been increased and the maximum value of micro-hardness generated near the surface due to LSP. The optimum thickness of DDDW layer was 4mm. After this thickness (4mm) ,the results of microhardness and surface roughness are reduced due to the absorption of laser pulse energy by the confinement layer .

A GaAs-based self-aligned stripe distributed feedback laser

We demonstrate operation of a GaAs-based self-aligned stripe (SAS) distributed feedback (DFB) laser. In this structure, a first order GaInP/GaAs index-coupled DFB grating is built within the p-doped AlGaAs layer between the active region and the n-doped GaInP opto-electronic confinement layer of a SAS laser structure. In this process no Al-containing layers are exposed to atmosphere prior to overgrowth. The use of AlGaAs cladding affords the luxury of full flexibility in upper cladding design, which proved necessary due to limitations imposed by the grating infill and overgrowth with the GaInP current block layer. Resultant devices exhibit single-mode lasing with high side-mode-suppression of >40 dB over the temperature range 20 °C–70 °C. The experimentally determined optical profile and grating confinement correlate well with those simulated using Fimmwave.

Uniform fuel target implosion in heavy ion inertial fusion

For a steady operation of a fusion power plant the target implosion should be robust against the implosion non-uniformities. In this paper the non-uniformity mitigation mechanisms in the heavy ion beam (HIB) illumination are discussed in heavy ion inertial fusion (HIF). A density valley appears in the energy absorber, and the large-scale density valley also works as a radiation energy confinement layer, which contributes to the radiation energy smoothing for the HIB illumination non-uniformity. The large density-gradient scale, which is typically ∼500μm in HIF targets, also contributes to a reduction of the Rayleigh- Taylor instability growth rate. In HIF a wobbling HIBs illumination would also reduce the Rayleigh-Taylor instability growth and to realize a uniform implosion.

Research status and development of laser shock peening

Laser shock peening (LSP) is a noncontact surface strengthening technology. It has been widely used because of its advantages in applied scope and strengthening effects. LSP has made considerable progress during the past four decades, but some technical issues affecting their applications remain to be resolved, for instance, the utilization rate of laser shock energy is only about 50%, the processing adaptability of rigid confinement layer is poor, and the thickness of the flexible confinement layer represented by a water layer is difficult to control. In this paper, the current research status of LSP technology was reviewed, and an outlook was given toward further development of this technology. On this basis, a method to form composite shock waves by designing a cavity to confine the water layer is presented in this paper, which is expected to address the issues mentioned above. A preliminary simulation for analyzing the relationship between the strengthening effect and the characteristic parameters of the composite shock wave was carried out, and the simulated results were discussed. The results show that the time interval between the adjacent waves and the wave attenuation factor have significant influence on the strengthening effects, which is helpful to the cavity design.

Tin nanoparticles encapsulated in graphene backboned carbonaceous foams as high-performance anodes for lithium-ion and sodium-ion storage

A new type of hierarchical tin@carbon composite composed of graphene carbonaceous matrix and well-confined tin nanoparticles with a typical size of ~15nm (denoted as F-G/Sn@C) is developed and investigated as anode material for Li-ion and Na-ion storage. The two dimensional graphene backboned matrix not only acts as a confinement layer preventing the tin nanoparticles from aggregating during the material preparation, but also functions as a physical barrier to buffer the volume change effect during charge/discharge processes. As a consequence, the composite demonstrates excellent rate performance and cycling stability for both Li-ion and Na-ion storage. In particular, the F-G/Sn@C anode exhibits an impressive reversible capacity of 506mAh g−1 even after 500 cycles and a high-rate capacity of 270mAh g−1 even at 3200mAg−1 for Li-ion storage. Moreover, a reversible Na-ion storage capacity of 413 mAh g−1 with negligible fading is also achieved. The remarkable electrochemical performance, together with the facile synthetic approach for large scale production, enables such material as a highly attractive tin-based anode for next generation rechargeable batteries.

Effect of Confinement Layer on Laser Ablation and Cavitation Bubble during Laser Shock Peening

Laser shock peening (LSP) is one of surface treatments to induce residual compressive stresses near metal surface to improve the resistance of materials to surface-related failures, such as fatigue and stress corrosion cracking. In LSP process, short pulsed laser is focused and irradiated to the material covered by transparent overlay such as glass or water. This transparent overlay is also known as a confinement layer and has an important role to increase impact pressure during LSP process. When confinement layer is liquid, the characteristics of the layer such as temperature, viscosity, etc. affect the phenomena occurring during the peening process and undoubtedly influence the induced residual stress. In the present study, Acoustic Emission (AE) technique coupling with high speed camera was applied to study the effect of confinement layer on LSP process. The results were discussed using the impact force calculated by inverse analysis of detected AE waveforms and bubble parameters observed by high speed camera. The results showed that temperature, thickness and viscosity of confinement layer had strong influence on the generation and collapse of cavitation bubble. The optimization of process parameters could be obtained by AE technique.

LP-MOVPE growth and properties of high Si-doped InGaAs contact layer for quantum cascade laser applications

AbstractThe work presents doping characteristics and properties of high Si−doped InGaAs epilayers lattice−matched to InP grown by low pressure metal−organic vapour phase epitaxy. Silane and disilane were used as dopant sources. The main task of investigations was to obtain heavily doped InGaAs epilayers suitable for usage as plasmon−confinement layers in the construction of mid−infrared InAlAs/InGaAs/InP quantum−cascade lasers (QCLs). It requires the doping concentration of 1×10

Insights into charge balance and its limitations in simplified phosphorescent organic light-emitting devices

Simplified phosphorescent organic light-emitting device (PHOLED), which utilizes only two organic layers, showed record-high efficiency when first introduced. It is quite surprising that this device can have such high efficiency without the use of complex carrier and exciton confinement layers that are common in the state-of-the-art PHOLEDs nowadays. Therefore, it is important to understand how good charge balance is in simplified PHOLED and why. In this work, we study the effects of altering charge balance in simplified PHOLED through means of changing layer thickness in the hole transport layer (HTL) and electron transport layer (ETL) as well as intentionally doping hole and electron traps in the HTL and ETL, respectively, on device efficiency. The results show that when using high carrier mobility charge transport materials, changing layer thickness does not impact charge balance appreciably. On the other hand, introducing charge traps in a thin layer within the HTL or ETL can, in comparison, influence charge balance more significantly, and proves to be a more effective approach for studying the factors limiting charge balance in these devices. The results reveal that simplified PHOLEDs are generally hole-rich, and that the leakage of electrons to the counter electrode is also a major mechanism behind the poor charge balance and efficiency loss in these devices. In order to optimize charge balance in simplified PHOLED, it is important to reduce hole transport in the device so that e-h ratio can be brought closer to unity, as well as eliminate electron leakage. Finally, we show that by simply using an electron blocking HTL, the efficiency of the device can be enhanced by as much as 25%, representing the highest reported for simplified PHOLEDs.

Output power of a quantum dot laser: Effects of excited states

A theory of operating characteristics of quantum dot (QD) lasers is discussed in the presence of excited states in QDs. We consider three possible situations for lasing: (i) ground-state lasing only; (ii) ground-state lasing at first and then the onset of also excited-state lasing with increasing injection current; (iii) excited-state lasing only. The following characteristics are studied: occupancies of the ground-state and excited-state in QDs, free carrier density in the optical confinement layer, threshold currents for ground- and excited-state lasing, densities of photons emitted via ground- and excited-state stimulated transitions, output power, internal and external differential quantum efficiencies. Under the conditions of ground-state lasing only, the output power saturates with injection current. Under the conditions of both ground- and excited-state lasing, the output power of ground-state lasing remains pinned above the excited-state lasing threshold while the power of excited-state lasing increases. There is a kink in the light-current curve at the excited-state lasing threshold. The case of excited-state lasing only is qualitatively similar to that for single-state QDs—the role of ground-state transitions is simply reduced to increasing the threshold current.

Fundamental transverse mode selection and self-stabilization in large optical cavity diode lasers under high injection current densities

It is shown that in high-power, large optical cavity laser diodes at high injection currents, the optical losses due to nonuniform carrier accumulation in the optical confinement layer can ensure the laser operation in the fundamental transverse mode. An experimental demonstration of switching from second order mode to fundamental mode in large optical cavity lasers with current and/or temperature increase is reported and explained, with the calculated values for the switching current and temperature in good agreement with the measurements. The results experimentally prove the nonuniform nature of carrier accumulation in the confinement layer and may aid laser design for optimizing the output.

InAs-Based Single-Mode Distributed Feedback Interband Cascade Lasers

InAs-based single-mode distributed feedback (DFB) interband cascade (IC) lasers were investigated. The DFB grating was patterned using interference lithography to etch the cladding-free upper separate confinement layer of the IC laser structure. Single-mode emission with a side mode suppression ratio of $\sim 30$ dB was obtained in continuous wave operation at temperatures up to 180 K near 4.5 $\mu \text{m}$ . A total tuning range of 16 nm could be achieved for a single device, with typical temperature- and current-tuning rates of 0.4 nm/K and 0.016 nm/mA, respectively. The impact of the DFB grating on device performance was evaluated and discussed in comparison with Fabry–Perot lasers.

Fabrication and optimization of 1.55-μm InGaAsP/InP high-power semiconductor diode laser**Project supported by the National Natural Science Foundation of China (Nos. 61274046, 61201103) and the National High Technology Research and Development Program of China (No. 2013AA014202).

A comprehensive design optimization of 1.55-μm high power InGaAsP/InP board area lasers is performed aiming at increasing the internal quantum efficiency (ηi) while maintaining the low internal loss (αi) of the device, thereby achieving high power operation. Four different waveguide structures of broad area lasers were fabricated and characterized in depth. Through theoretical analysis and experiment verifications, we show that laser structures with stepped waveguide and thin upper separate confinement layer will result in high ηi and overall slope efficiency. A continuous wave (CW) single side output power of 160 mW was obtained for an uncoated laser with a 50-μm active area width and 1 mm cavity length.

Luminous efficiency enhancement in blue phosphorescent organic light-emitting diodes with an electron confinement layers

This study reports the results of blue phosphorescent organic light emitting diodes (PHOLEDs) employing an electron confinement layer (ECL), tris-(phenylpyrazole)iridium (Ir(ppz)3) and a hole confinement layer (HCl), 1,3,5-tris(N-phenylbenzimiazole-2-yl)benzene (TPBi). The electrical and optical characteristics of PHOLEDs with different emissive layers, including current density, luminance, and luminous efficiency, were analyzed. The thickness of the individual emissive layer was optimized, however, and the total thickness of the emitting region was kept constant at 300Å. This work reveals that the effective electron confinement, due to a large energy level offset between the electron confinement and emitting layers, helps to improve hole–electron current balance in the emitting region. The maximum external quantum efficiency of 23.40% at 1500cd/m2 was achieved for PHOLEDs with an ECL, which is 60% higher than the structural identical control device without ECL.

Uniformity of fuel target implosion in heavy ion fusion

AbstractIn inertial confinement fusion the target implosion non-uniformity is introduced by a driver beams’ illumination non-uniformity, a fuel target alignment error in a fusion reactor, the target fabrication defect, etc. For a steady operation of a fusion power plant the target implosion should be robust against the implosion non-uniformities. In this paper the requirement for the implosion uniformity is first discussed. The implosion uniformity should be less than a few percent. A study on the fuel hotspot dynamics is also presented and shows that the stagnating plasma fluid provides a significant enhancement of vorticity at the final stage of the fuel stagnation. Then non-uniformity mitigation mechanisms of the heavy-ion beam (HIB) illumination are also briefly discussed in heavy ion inertial fusion (HIF). A density valley appears in the energy absorber, and the large-scale density valley also works as a radiation energy confinement layer, which contributes to a radiation energy smoothing. In HIF a wobbling HIB illumination was also introduced to realize a uniform implosion. In the wobbling HIBs illumination, the illumination non-uniformity oscillates in time and space on a HIF target. The oscillating-HIB energy deposition may contribute to the reduction of the HIBs’ illumination non-uniformity by its smoothing effect on the HIB illumination non-uniformity and also by a growth mitigation effect on the Rayleigh–Taylor instability.

Suppression of sublinearity of light–current curve in 850 nm quantum well laser with asymmetric barrier layers

An AlGaAs/GaAs quantum well (QW) laser is fabricated with GaInP and AlGaInAs asymmetric barrier layers (ABLs) and its light–current characteristic (LCC) is compared with that of a reference conventional QW laser without ABLs. It was found that the use of the ABLs suppresses the sublinearity of the LCC at high current densities. As a result, the maximum lasing power of 9.2 W, being limited by catastrophic optical mirror damage, is achieved at a considerably lower operating current in the laser with ABLs as compared to the reference laser (12.5 against 20.2 A). The ABL effect is associated with the suppression of the parasitic recombination in the optical confinement layer, as confirmed by a decrease of the intensity of the spontaneous emission from the layer.

Interfacial structure of water/methanol mixture in contact with graphene surface using molecular dynamics simulation

The interaction of an interfacial water/methanol binary mixture with a graphene surface at the atomic scale was investigated by means of molecular dynamics simulation. The contact angle of a pure water droplet and three different concentrations of a water/methanol binary mixture were investigated on the charged and neutral forms of the graphene surface at room temperature. The mass density distribution functions of water, methanol and their binary mixtures were calculated, representing the microscopic structural properties. The novel effects of confinement and charged graphene layers on the interfacial structure of water/methanol system were investigated. The surface tension of mixtures was also calculated and the results were compared to the experimental data.

Optimization of High Power 1.55-μm Single Lateral Mode Fabry—Perot Ridge Waveguide Lasers**Supported by the National Natural Science Foundation of China under Grant Nos 61274046 and 61474111, and the National Basic Research Program of China under Grant No 2013AA014202.

Optimization of the high power single-lateral-mode double-trench ridge waveguide semiconductor laser based on InGaAsP/InP quantum-well heterostructures with a separate confinement layer is reported. Two different waveguide structures of Fabry—Perot lasers emitting at a wavelength of 1.55 μm are fabricated. The influence of an effective lateral refractive index step on the maximum output power is investigated. A cw single mode output power of 165 mW is obtained for a 1-mm-long uncoated laser.

Large Area Silica Nano Grids by Homogeneous High Resolution Laser Patterning of SiOx-Films

Structured excimer laser back side irradiation of thin SiOx-films on fused silica substrates is used for the formation of complex micro- and nano-patterns. A polymeric superstrate serving as a confinement layer on top of the SiOx-film allows the formation of very smooth and regular patterns. Depending on laser processing parameters, either arrays of blisters or cups, or grids with free standing wires below 100 nm in diameter can be fabricated. To obtain these nano-features with high structure resolution on a comparatively large area with a single KrF-laser pulse (wavelength 248 nm), an optical system combining a beam homogenizer with a high resolution mask imaging optical system has been established. At fluences in the range of 300 to 400 mJ/cm² very regular grid patterns with wires detached from the substrate and nodes attached to the substrate are obtained. The free standing wires have diameters down to less than 100 nm. The patterned SiOx-material can be oxidized to SiO2 by thermal or laser treatment.

Observation of Room Temperature Photoluminescence from Asymmetric CuGaO2/ZnO/ZnMgO Multiple Quantum Well Structures.

Asymmetric (CuGaO2/ZnO/ZnMgO) and symmetric (ZnMgO/ZnO/ZnMgO) multiple quantum well (MQW) structures were successfully fabricated using pulsed laser deposition (PLD) and their comparison were made. Efficient room temperature photoluminescent (PL) emission was observed from these MQWs and temperature dependent luminescence of asymmetric and symmetric MQWs can be explained using the existing theories. A systematic blue shift was observed in both MQWs with decrease in the confinement layer thickness which could be attributed to the quantum confinement effects. The PL emission from asymmetric and symmetric MQW structures were blue shifted compared to 150 nm thick ZnO thin film grown by PLD due to quantum confinement effects.