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

Abstract

Article:Savić, I., Vukmirović, N., Ikonić, Z. et A density matrix theory of electron transport and optical gain in quantum cascade lasers in an external magnetic field is formulated. Starting from a general quantum kinetic treatment, we describe the intraperiod and interperiod electron dynamics at the non-Markovian, Markovian, and Boltzmann approximation levels. Interactions of electrons with longitudinal optical phonons and classical light fields are included in the present description. The non-Markovian calculation for a prototype structure reveals a significantly different gain spectra in terms of linewidth and additional polaronic features in comparison to the Markovian and Boltzmann ones. Despite strongly controversial interpretations of the origin of the transport processes in the nonMarkovian or Markovian and the Boltzmann approaches, they yield comparable values of the current densities.

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

“…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.…”

“…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.…”

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

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

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

“…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.…”

“…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].…”