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ABSTRACT: We examine the electronic structure and optical properties of 1.5-μm InAs/InGaAsP/InP quantum dash-in-a-well (DWELL) and dash-in-a-barrier (DBAR) lasers. Using 1-D and 3-D k.p calculations, we show that the electron states are not confined to the dash layer in the DWELL structures and are poorly confined in the DBAR case, due to the small conduction band offset in InGaAsP systems. The built-in strain induces a large HH-LH splitting, resulting in a significant reduction in the calculated valence band density of states (DOS). Coupled together, these properties can be engineered to give a nearly symmetric conduction and valence band DOS within 0.1 eV of the band edge. The calculated gain due to light polarized along the TE(110) and TE(1-10) directions is anisotropic, with the degree of anisotropy dependent on the dash height and the area density of the dashes. We conclude that the dashes can provide a high modal gain with reduced transparency and threshold carrier density but similar threshold current density compared to equivalent quantum well devices.
IEEE Journal of Quantum Electronics 06/2010; · 1.88 Impact Factor
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ABSTRACT: In this work, we explore the use of strained InGaAs/AlGaAs QWs and benchmark the performance against conventional GaAs/AlGaAs QWs.VCSELs with an optimized InGaAs/AlGaAs QW active region have a modulation bandwidth of 20 GHz at 25degC and 15 GHz at 85degC and have enabled error-free transmission over 50 (100) m multimode fiber up to 32 (25) Gb/s at a bias current density as low as 11 kA/cm<sup>2</sup> under direct current modulation.
Lasers and Electro-Optics 2009 and the European Quantum Electronics Conference. CLEO Europe - EQEC 2009. European Conference on; 07/2009
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ABSTRACT: There remains controversy surrounding the cause of the magnitude and temperature sensitivity of the threshold current density of 1.3-μm GaInNAs quantum-well (QW) lasers, with several authors attributing the strong temperature sensitivity to hole leakage, due to the relatively low valence band offset in GaInNAs/ GaAs QW structures. We use a Poisson solver along with a ten-band k.p Hamiltonian to calculate self-consistently the influence of electrostatic confinement on the optical gain in such lasers. We find that the inclusion of such effects significantly reduces the hole leakage effect, with the electrostatic attraction of the electrons significantly increasing the binding of heavy holes in the QW region. We conclude by comparison with previous theoretical and experimental studies that the room temperature threshold current is generally dominated by monomolecular recombination, while the temperature sensitivity can be explained as predominantly due to Auger recombination.
IEEE Journal of Quantum Electronics 07/2006; · 1.88 Impact Factor
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ABSTRACT: Conventionally finite difference methods are used to solve a multi-band k.p Hamiltonian in quantum well and heterostructure systems where a self consistent solution of Poisson's equation is important, due e.g. to the presence of a Type II band line-up, with electrons and holes confined in separate layers. Following similar methods to density functional theory we describe a plane wave expansion method to efficiently solve a multi-band k.p Hamiltonian self consistently, including a fast Fourier space solution of Poisson's equation. We demonstrate the efficiency of the method by considering the potential in an InGaAs/InGaAsP/InP 1.5 μm laser.
Numerical Simulation of Optoelectronic Devices, 2005. NUSOD '05. Proceedings of the 5th International Conference on; 10/2005
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ABSTRACT: The band-anti-crossing (BAC) model successfully describes many of the electronic properties of GaN<sub>x</sub>As<sub>1-x</sub>. Experimental and theoretical studies show a range of resonant defect levels close to the conduction band edge in GaN<sub>x</sub>As<sub>1-x</sub>, due to the formation of N complexes which are ignored in the conventional BAC model. The consequences of these resonant levels for the band dispersion are investigated. The rapid increase in N-N pairs with N composition (∝x<sup>2</sup>) is shown to have little effect on the calculated room-temperature band-edge dispersion, but modifies the low-temperature band dispersion with increasing x. For low temperatures, it is shown that at low N composition (0.001≤x≤0.01) the band dispersion is best described using a modified BAC model, which explicitly includes the effects of N-N pairs, while at higher compositions (x>0.01) the effects of longer-range N-N interactions need also to be considered. The consequences of this are analysed for the predicted evolution of band dispersion with x in magneto-tunnelling experiments.
IEE Proceedings - Optoelectronics 11/2004; · 0.71 Impact Factor
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ABSTRACT: This work analyzes the influence of Coulomb effects with increasing degree of complexity, starting with the Hartree-Fock limit, and evolving to the screened Hartree-Fock case and further on to beyond Hartree-Fock corrections, including non-diagonal dephasing contributions to both interband and intersubband transitions. Electron-electron, hole-hole and electron-hole transitions, correlation and scattering mechanisms are systematically included in our many body Greens functions formalism that consistently includes the nonparabolic electron and hole dispersion relations as well as independent transition dipole elements obtained from a rigorous solution of an 8 × 8 k.p Hamiltonian. The carrier-induced absorption/gain coefficient and refractive index change are directly calculated from the imaginary, χ" and real, χ' parts of the optical susceptibility function.
Numerical Simulation of Optoelectronic Devices, 2004. NUSOD '04. Proceedings of the 4th International Conference on; 09/2004
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ABSTRACT: Recent low-temperature scanning tunneling experiments have questioned the generally accepted picture of buckled silicon dimers as the ground state reconstruction of the Si(100) surface, undermining the ability of density functional theory to accurately describe electronic correlations at surfaces. We present quantum Monte Carlo calculations on large cluster models of the surface, and conclude that buckling remains energetically favorable even when the present-day best treatment of electronic correlation is employed. The implications for experimental interpretation are discussed.
Physical Review Letters 08/2001; 87(1):016105. · 7.37 Impact Factor
