Density matrix theory of transport and gain in quantum cascade lasers in a magnetic field

Savić, Ivana; Vukmirović, Nenad; Ikonić, Z.; Indjin, D.; Kelsall, R. W.; Harrison, P.; Milanović, V.

doi:10.1103/physrevb.76.165310

Cited by 41 publications

(26 citation statements)

References 42 publications

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“…This is an approximation often applied within the Born-Markov approximation. 25,38 Since the renormalizations, like the scattering rates, are temperature-dependent, this could explain why the convergence problems only appear for certain temperatures. On the other hand, since the resonances depend on the specific energy structure, and thus on the barrier width b, problems are expected to appear only for certain barrier widths, as witnessed in the results.…”

Section: Shortcomings Of the Modelmentioning

confidence: 99%

“…The stationary properties of QCLs were studied by a rate equation 10,11 and a Boltzmann-type approach 12,13,14,15,16,17 as well as a quantum theory employing both nonequilibrium Green's functions 18,19,20,21,22 and density-matrix theory. 23,24,25 Here, the gain, the current-voltage characteristics, and the stationary charge distributions have been established. First results regarding the nonlinear optical properties such as optically induced subband population dynamics have been presented by us within a density-matrix theory.…”

Section: Quantum Cascade Lasers (Qcls)mentioning

confidence: 99%

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Density-matrix theory of the optical dynamics and transport in quantum cascade structures: The role of coherence

2009

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The impact of coherence on the nonlinear optical response and stationary transport is studied in quantum cascade laser structures. Nonequilibrium effects such as pump-probe signals, the spatio-temporally resolved electron density evolution, and the subband population dynamics (Rabi flopping) as well as the stationary current characteristics are investigated within a microscopic density-matrix approach. Focusing on the stationary current and the recently observed gain oscillations, it is found that the inclusion of coherence leads to observable coherent effects in opposite parameter regimes regarding the relation between the level broadening and the tunnel coupling across the main injection barrier. This shows that coherence plays a complementary role in stationary transport and nonlinear optical dynamics in the sense that it leads to measurable effects in opposite regimes. For this reason, a fully coherent consideration of such nonequilibrium structures is necessary to describe the combined optical and transport properties.

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Section: Shortcomings Of the Modelmentioning

confidence: 99%

Section: Quantum Cascade Lasers (Qcls)mentioning

confidence: 99%

Density-matrix theory of the optical dynamics and transport in quantum cascade structures: The role of coherence

2009

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“…21,22 Also a quantum-dash cascade structure was proposed. 23 Another possibility is to use self-assembled quantum dots (QDs).…”

Section: -20mentioning

confidence: 99%

Microscopic model for intersubband gain from electrically pumped quantum-dot structures

2014

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We study theoretically the performance of electrically pumped self-organized quantum dots as a gain material in the mid-IR range at room temperature. We analyze an AlGaAs/InGaAs based structure composed of dots-in-a-well sandwiched between two quantum wells. We numerically analyze a comprehensive model by combining a many-particle approach for electronic dynamics with a realistic modeling of the electronic states in the whole structure. We investigate the gain both for quasi-equilibrium conditions and current injection. Comparing different structures we find that steady-state gain can only be realized by an efficient extraction process, which prevents an accumulation of electrons in continuum states, that make the available scattering pathways through the quantum dot active region too fast to sustain inversion. The tradeoff between different extraction/injection pathways is discussed. Comparing the modal gain to a standard quantum-well structure as used in quantum cascade lasers, our calculations predict reduced threshold current densities of the quantum dot structure for comparable modal gain. Such a comparable modal gain can, however, only be achieved for an inhomogeneous broadening of a quantum-dot ensemble that is close to the lower limit achievable today using self-organized growth.

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“…The highest operating temperature of 225K is reported for resonant-phonon design scheme assisted by external magnetic field for additional carrier confinement [3]. The role of the magnetic field is to suppress non-radiative intersubband relaxation processes and thus increase the optical gain [1,3,[8][9][10][11][12][13][14][15][16][17][18]. Hence, detailed understanding of various scattering mechanisms, * corresponding author; e-mail: radovanovic@etf.bg.ac.rs relevant for laser operation, may be an important factor in improving its performance.…”

Section: Introductionmentioning

confidence: 99%

“…However, the impressive performances obtained by quantum cascade lasers (QCL)s in the mid-infrared spectral region, in terms of operating temperature, output power and tunability, cannot easily be transferred to longer wavelengths. The performances of THz QCLs deteriorate rapidly with temperature due to detrimental thermal activation of nonradiative losses [8], so cryogenic cooling is still required for their operation. The highest operating temperature of 225K is reported for resonant-phonon design scheme assisted by external magnetic field for additional carrier confinement [3].…”

Section: Introductionmentioning

confidence: 99%

Inter-Landau Level Scattering Processes in Magnetic Field Assisted THz Quantum Cascade Laser

et al. 2011

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We present a detailed analysis of GaAs/AlGaAs terahertz quantum cascade laser in the presence of an intense external magnetic field. One of the objectives in further development of THz quantum cascade laser is the realization of structures operating at higher temperatures. This is difficult to obtain as the operating photon emission energy is smaller than the longitudinal-optical phonon energy in the semiconductor material. With increased temperature, electrons in the upper radiative state gain sufficient in-plane energy to emit an longitudinal-optical phonon, which represents a non-radiative scattering and reduces the optical gain. By applying strong magnetic field, two-dimensional continuous energy subbands become split into series of discrete Landau levels, and at particular values of B it is possible to quench these non-radiative channels. Numerical simulations are performed on two-well design quantum cascade laser operating at 4.6 THz, implemented in GaAs/Al0.15Ga0.85As, and the magnetic field is perpendicular to the epitaxial layers. Strong oscillations of carrier lifetimes for the upper state of the laser transition, as a function of magnetic field are observed, which can be attributed to interface roughness scattering and longitudinal-optical phonon scattering between Landau levels.

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Density matrix theory of transport and gain in quantum cascade lasers in a magnetic field

Cited by 41 publications

References 42 publications

Density-matrix theory of the optical dynamics and transport in quantum cascade structures: The role of coherence

Density-matrix theory of the optical dynamics and transport in quantum cascade structures: The role of coherence

Microscopic model for intersubband gain from electrically pumped quantum-dot structures

Inter-Landau Level Scattering Processes in Magnetic Field Assisted THz Quantum Cascade Laser

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