292 research outputs found
Effects of annealing on self-organized InAs quantum islands on GaAs (100)
No full textSelf-organized InAs islands on (001) GaAs grown by molecular beam epitaxy were annealed and characterized with photoluminescence (PL) and transmission electron microscopy (TEM). The PL spectra from the InAs islands demonstrated that annealing resulted in a blueshift in peak energy, a reduction in intensity, and a narrower linewidth in the PL peak. In addition, the TEM analysis revealed the relaxation of strain in some InAs islands with the introduction of the network of 90 degrees dislocations. The correlation between the changes in the PL spectra and the relaxation of strain in InAs islands was discussed. (C) 1998 American Institute of Physics. [S0003-6951(98)01850-6]
An operational analysis of shell planting strategies for improving the survival of oyster larvae in the Chesapeake Bay
No full textMaryland's oyster fishery has declined dramatically since 1930. Meanwhile, recent studies have shown that careful management of the shell planting process can lead to increased oyster yields. This is due to the fact that oyster larvae that attach to fossil shells at the bottom of the Chesapeake Bay have a greatly enhanced likelihood of survival. In this paper, we indicate how linear programming and a rule-based heuristic can be used in tandem to determine effective sites and schedules for shell planting. In particular, linear programming is used to address the macro problem of deciding where to plant the shells, subject to high-level constraints. The rule-based heuristic addresses the micro problem of scheduling tugboats, barges, and the planting crew, subject to more detailed constraints.Computer Science, Information SystemsOperations Research & Management ScienceSCI(E)0ARTICLE3181-1963
Design of 1.55 um InGaAsNBi/GaAs quantum well laser
No full textThe use of InGaAs/GaAs quantum well (QW) lasers has started to become prevalent in fiber communications. It is found that by operating at 1.55um minimal optical loss can be achieved. Bismide has been added so as to achieve the ideal 1.55um wavelength for the QW laser. Simulations with varying bismide compositions have been run so as to find which bismide composition would achieve the desired 1.55um wavelength. A graph depicting the relationship between various QW widths (WW) versus the bandgap energy has been plotted.Bachelor of Engineerin
Orientation dependence of electronic structure and optical gain of (11N)-oriented III-V-N quantum wells
No full textA ten-band k ∙p Hamiltonian for III-V-N dilute nitride semiconductor quantum wells (QWs) grown
on the (11N)-oriented substrates is presented. The energy dispersion curves, optical transition
matrix elements, internal piezoelectric field, and optical gain of InGaAsN/GaAs on the (110),
(111), (113), and (11∞)-oriented substrates are investigated including band-anti-crossing, strain,
and piezoelectric field effects. The band structures and optical gain are sensitive to the substrate
orientation. The fundamental transition energy is the largest for the (111)-oriented QW and the
smallest for (11∞)-oriented QW. The absolute values of internal piezoelectric field in the well and
barrier layers reach the maximum for the (111)-QW, and zero for the (110) and (11∞)-oriented
QWs. There exists an injection current density turning point. When the injection current density is
below the turning point, the (111)-oriented QW has the largest peak gain. At the larger injection
current density, the (11∞)-oriented QW has the largest peak gain.Published versio
Arsenic clusters on the surface of vertically aligned InAs islands on GaAs substrate by annealing
No full textThe formation of arsenic clusters in a system of vertically aligned InAs quantum islands on GaAs during thermal annealing under As overpressure has been investigated by transmission electron microscopy (TEM) and Raman scattering. Semicoherent arsenic clusters, identified by TEM examination, have been formed on the surface of the GaAs capping layer. The existence of arsenic precipitates is also confirmed by Raman spectra, showing new peaks from the annealed specimen at 256 and 199 cm(-1). These peaks have been ascribed to A(1g) and E-g Raman active phonons of crystalline arsenic. The phenomenon can be understood by a model of strain-induced selected growth under As overpressure. (C) 1999 American Institute of Physics. [S0003-6951(99)02045-8]
Tensile strained ge pseudo-heterostructure quantum wells
No full textGe semiconductor has received great attention recently due to its potential application in optoelectronic devices, such as Laser and LED diodes. Ge is an indirect band gap semiconductor, which results in a poor optical transition probability. However, the laser emission from the direct band transition at room temperature was observed and reported in heavy n-type doped tensile strained Ge-on-Si material recently.[1] Band structures of tensile strained and n+ doped Ge/Ge0.986Si0.014 quantum wells (QWs) are calculated by multiple-band k·p method[7]. In this work, we propose a Ge quantum well (QW) caused by the uniaxial tensile strain, which may be realized by the micro-bridge technique.[2,3] Because the QW is formed by Ge only, it is called as the Ge pseudo-heterostructure QW (PQW).Bachelor of Engineering (Electrical and Electronic Engineering
Tensile strained ge pseudo-heterostructure quantum wells
No full textGe semiconductor has received great attention recently due to its potential application in optoelectronic devices, such as Laser and LED diodes. Ge is an indirect band gap semiconductor, which results in a poor optical transition probability. However, the laser emission from the direct band transition at room temperature was observed and reported in heavy n-type doped tensile strained Ge-on-Si material recently.[1] Band structures of tensile strained and n+ doped Ge/Ge0.986Si0.014 quantum wells (QWs) are calculated by multiple-band k·p method[7]. In this work, we propose a Ge quantum well (QW) caused by the uniaxial tensile strain, which may be realized by the micro-bridge technique.[2,3] Because the QW is formed by Ge only, it is called as the Ge pseudo-heterostructure QW (PQW).Bachelor of Engineering (Electrical and Electronic Engineering
Spectral and Transient Luminescence Measurements on GaSb/AlGaSb Quantum Wells Grown on GaSb/GaAs Heterojunctions with and without Interfacial Misfit Arrays
No full textGrowth of 90° interfacial-misfit-dislocation (IMF) array at heterointerfaces offers low dislocation densities in highly mismatched heterostructures such as GaSb/GaAs. We investigated time-integrated and time-resolved photoluminescence (PL) properties of a GaSb/AlGaSb quantum well (QW) structure grown on (001) GaAs substrate with and without IMF array at the GaSb-buffer/GaAs interface. Our observation reveals that the low-temperature PL from the QW with IMF is twice more intense than that of the QW without IMF, indicating higher quantum efficiency with IMF. The QW with IMF also exhibited the band filling effect at higher excitation power revealed from the spectrally resolved PL decay measurements. These results are the indication of subdued dislocation density with the IMF growth mode. Our PL measurement results along with supportive band-structure calculation of the GaSb/AlGaSb QW show that the luminescence efficiency of the present QW structure is limited by the hole leakage at elevated temperature. Therefore the IMF effect will be more clearly demonstrated by replacing the heterostructure with the one with higher band-offsets
Carrier lifetime and recombination in long-wavelength quantum-well lasers
No full textWe present a novel analysis for correcting the measured differential carrier lifetime to account for carrier population in both the barrier and separate confinement heterostructure (SCH) regions of quantum-well (QW) lasers. This analysis uses information obtained from the measured spontaneous emission spectra to correct the measured lifetime and obtain the intrinsic well lifetime. Once the intrinsic well lifetime is obtained, the intrinsic well recombination coefficients can also be obtained. We show that the carrier population in the barrier/SCH layers can significantly affect the measured carrier lifetime and the extracted recombination coefficients. We also show that this analysis yields transparency carrier density and differential gain numbers which are very different from those obtained with the traditional analysis and much closer to what is predicted for highly strained QW lasers. These differences indicate the importance of accounting for barrier/SCH carriers on the measurement of basic QW laser material properties.This work was supported by the National Science Foundation under Grants ECS 9408321 and DMR 9803066
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