Influence Of Barrier Materials Research Articles

Enhancement of photoluminescence of GaAsBi quantum wells by parabolic design of AlGaAs barriers

Influence of barrier material and structure on carrier quantum confinement in GaAsBi quantum wells (QWs) is studied comprehensively. Single- and multi-QW structures were grown using solid-state molecular beam epitaxy with conventional rectangular, step-like and parabolically graded AlGaAs barrier designs. It was discovered that room temperature photoluminescence is increased by more than 50 times in the GaAsBi QWs with parabolically graded barriers (PGBs) if compared to standard rectangular and step-like structures. The enhancement of photoluminescence was reproducible within the range of growth parameters. The carrier localization and increase of trapping efficiency in GaAsBi QWs is responsible for observed enhancement in radiative properties of PGB structures. The random potential field fluctuations for carriers were increased up to 44 meV due to the blurred well-barrier interface causing the conditions for Bi content and/or well width variations. Due to the impact of self-organizing effects on the reproducibility of optical properties, the GaAsBi QWs with AlGaAs PGBs open the window for fabrication of 1.0–1.55 μm wavelength emission lasers based on GaAsBi quantum structures.

Influence of barrier material and barrier shape on blast wave mitigation

This paper investigates means for increasing the effectiveness of a blast barrier using various types of surfacing. It builds on previous research on the blast effect mitigation properties of rigid concrete blast barriers. Previous research has studied barriers with a smooth surface. The effectiveness of rigid smooth barriers in reducing shock wave overpressure has been proven to be low. Their main contribution is in absorbing flying debris or shrapnel created by an explosion, and thereby reducing the risk of injury to the occupants of a building. This paper suggests ways to achieve greater safety by increasing the blast mitigation properties of barriers. It studies the influence of various materials and shapes on the effectiveness of a barrier, and proposes methods for providing increased overpressure reduction while keeping the same overall dimensions. A barrier of this kind provides additional security for the occupants of a building without disrupting the functionality of the interior with a massive obstacle. The use of a deformable porous material is compared with the use of rigid durable ultra-high performance fibre-reinforced self-compacting concrete (UHPFRSCC), developed by the authors especially for application in blast-resistant structures. The results of an original experimental program are used to determine the influence of barrier shape and barrier material on blast wave mitigation. The effect of uneven barrier surfacing on a shock wave is demonstrated on a finite element numerical model calculated using LS-DYNA. Results of the analysis proved that the use of uneven surface has a positive effect on blast mitigation properties of a barrier without affecting its shrapnel absorption capabilities. All experiments and FEM models consistently proved that a barrier has significant overpressure reduction effect in the area directly behind the barrier. The comparison of experimental measurements of rigid and deformable barrier material showed no drastic increase in mitigation properties of deformable barrier.

Spin-polarization in InAs/AlSb double barrier resonant tunneling structures: influence of barrier material and interface structure

We present a study on the atomistic simulation of the spin-polarized transmissions through InAs/AlSb double barrier resonant tunneling heterostructures. By making use of the atomistic sp3s* tight binding Hamiltonian including the intra-atomic spin-orbit interaction and the recursive Green’s function method, we obtain the significant anisotropic zero-magnetic-field spinsplitting of the resonant transmission peak in the absence of the external electric field, demonstrating the importance of the barrier material and the atomic scale detail of the hetero interfaces on the spin-splitting.

Experimental study on the transition of the discharge modes in air dielectric barrier discharge

Dielectric barrier discharge (DBD) usually manifests as a filamentary streamer discharge in atmospheric air, which limits its industrial application prospect, and the homogeneous DBD with homogeneity and stability has a wider application prospect in the field of material surface treatment, thin film deposition and plasma sterilization than the filamentary one. In order to study the generation condition for the homogeneous DBD in atmospheric air, the characteristics of DBD in the pressure range from 10 Pa to atmospheric pressure are experimentally studied by measuring their electrical discharge parameters and observing their light emission phenomena. The transition of the discharge mode with a change in pressure is observed, and a critical pressure value for generating the homogeneous DBD is obtained, with the influence of barrier materials, their thickness and surface roughness and the air gap distance on the critical pressure values being investigated experimentally. The experimental results show that three characteristic types of discharge modes, including the homogeneous mode, the mixed mode and the filamentary mode, are observed with an increase in pressure. The dielectric barrier plays an important role in the generation of the homogeneous DBD, and the critical pressure values will be larger if the barrier thickness is smaller and the air gap distance is smaller. The critical pd values (the product of gas pressure p and gas gap width d) are almost constant with the change in the air gap distance, which can be improved by reducing the thickness of the dielectric barrier and by selecting appropriate barrier materials, as is validated by the experimental results.

Influence of barrier material on spin splitting due to inversion asymmetry in heterostructures

Influence of barrier material on the spin splitting of conduction subbands in heterostructures because of structure inversion asymmetry (Bychkov–Rashba splitting) is studied. The spin splitting at a vanishing magnetic field is calculated for two heterostructures: InAs/SiO2 and InAs/In0.8Al0.2As, having the same well material InAs but very different barrier materials. It is demonstrated that the barrier material strongly influences the spin splitting of the ground conduction subband in InAs. The spin splittings for both heterostructures are computed as functions of electron density, we obtain the splitting in InAs/SiO2 almost twice larger than that in InAs/In0.8Al0.2As. The influence of spin-dependent part of the boundary conditions on the spin spin splitting is studied and it is shown that for considered heterostructures it changes the splitting up to 25% of its value. It is emphasized that the Bychkov–Rashba spin splitting is not proportional to the average electric field in heterostructure.

Investigation of indium segregation in InGaAs/(Al)GaAs quantum wells grown by MOCVD

Indium segregation in InGaAs/(Al)GaAs quantum wells (QWs) grown by low-pressure metal organic chemical vapor deposition (MOCVD) was studied. The QW heterostructures were grown at different substrate temperatures ( T=650–800°C) with and without growth interruption at specified interfaces. The influence of barrier materials (GaAs or AlGaAs) on indium distribution in QWs was investigated. Surface segregation of indium atoms during MOCVD was systematically studied using grazing sputter angle Auger electron spectroscopy and photoluminescence measurements. The increase of indium concentration in growth direction in single QWs and relative shift of composition in close-spaced double QWs were found. Optimization of the interruption time at specified interfaces, the increase of AlAs mole fraction in AlGaAs barrier and reduction of growth temperature resulted in the decrease of indium surface segregation. Indium segregation ratio R=0.91–0.94 was determined.