Regensburg 2007 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 9: Semiconductor Laser II

HL 9.2: Vortrag

Montag, 26. März 2007, 15:00–15:15, H13

Non-equilibrium quantum transport theory for quantum cascade lasers — •Tillmann Kubis and Peter Vogl — Walter Schottky Institut, Technische Universität München, Am Coulombwall 3, 85748 Garching

We present fully self-consistent non-equilibrium Green's function (NEGF) calculations of various quantum cascade laser structures (QCL) including all relevant coherent and incoherent scattering mechanisms. We have developed an implementation of the NEGF formalism that takes into account acoustic and polar-optical phonon scattering as well as impurity and interface roughness scattering within the self-consistent Born approximation. The complete momentum and energy dependence of all scattering mechanisms is accounted for. This is known to have a significant influence on all QCL device characteristics yet has been neglected in previous work. The electron-electron scattering is incorporated self-consistently within the Hartree approximation. The coupling between the lesser and the retarded Green's function is fully taken into account. In this way, all scattering states, transition probabilities between them, and their occupancies are calculated self-consistently instead of semi-classically. Our calculations yield I-V characteristics and optical gain that agree nicely with experiment. In spite of realistic dephasing, we observe multi-barrier tunneling and coherent formation of occupation inversion. Incoherent scattering mechanisms appear to assist tunneling but reduce the optical gain significantly.