Carrier dynamics in quantum-dot tunnel-injection structures: microscopic theory and experiment

TL;DR

This paper combines microscopic theory and experiments to analyze carrier dynamics in quantum-dot tunnel-injection structures, providing insights for optimizing tunnel-injection lasers by examining phonon-assisted tunneling and state confinement effects.

Contribution

It offers a detailed theoretical and experimental study of carrier tunneling and phonon interactions in quantum-dot structures, guiding laser optimization.

Findings

Quantum dots near the quantum well bottom benefit most from tunnel coupling.

Inhomogeneous broadening causes different coupling efficiencies among ensemble members.

Excited states become more confined with increased quantum dot depth, affecting phonon scattering.

Abstract

Tunneling-injection structures are incorporated in semiconductor lasers in order to overcome the fundamental dynamical limitation due to hot carrier injection by providing a carrier transport path from a cold carrier reservoir. The tunneling process itself depends on band alignment between quantum-dot levels and the injector quantum well, especially as in these devices LO-phonon scattering is dominant. Quantum dots with their first excited state near the quantum well bottom profit most from tunnel coupling. As inhomogeneous broadening is omnipresent in quantum dot structures, this implies that individual members of the ensemble couple differently to the injector quantum well. Quantum dots with higher energy profit less, as the phonon couples to higher, less occupied states. Likewise, if the energy difference between ground state and quantum well exceeds the LO phonon energy, scattering becomes increasingly inefficient. Therefore, within 20-30meV we find Quantum Dots that benefit substantially different from the tunnel coupling. Furthermore, in quantum dots with increasing confinement depth, excited states become sucessively confined. Here, scattering gets more efficient again, as subsequent excited states reach the phonon resonance with the quantum well bottom. Our results provide guidelines for the optimization of tunnel-injection lasers. Theoretical results for electronic state caluluations in connection with carrier-phonon and carrier-carrier scattering are compared to experimental results of the temporal gain recovery after a short pulse perturbation.