Interplay of structural design and interaction processes in tunnel-injection semiconductor lasers

Abstract

Tunnel-injection lasers promise various advantages in comparison to conventional laser designs. In this paper, the physics of the tunnel injection process is studied within a microscopic theory in order to clarify design requirements for laser structures based on quantum dots as active material and an injector quantum well providing excited charge carriers. We analyze how the electronic states of the injector quantum well and quantum dot levels should be aligned and in which way their coupling through the tunnel-injection barrier should be adjusted for optimal carrier injection rates into the quantum-dot ground state used for the laser transition. Our description of the tunnel-injection process combines two main ingredients: the tunnel coupling of the wave functions as well as the phonon-and Coulomb-assisted transition rates. For this purpose, material-realistic electronic state calculations for the coupled system of injector quantum well, tunnel barrier, and quantum dots are combined with a many-body theory for the carrier scattering processes. We find that the often assumed longitudinal-optical-phonon resonance condition for the level alignment has practically no influence on the injection rate of carriers into the quantum dot states. The structural design should provide optimal hybridization of the injector quantum well states with excited quantum dot states.

Performance of quantum-dot-based tunnel-injection lasers: A theoretical analysis

“…5 in Ref. 9 ), but not to a tuning to the LO-phonon energy as suggested previously 3 . The optimum of the modulation speed (for a particular device) is reached if the carrier scattering is fast enough to sustain a quasi-equilibrium situation.…”

“…To assess the advantages of TI lasers, we perform a comparison to a conventional QD-based laser design in the form of a dot-in-a-well (DWELL) structure. As shown in previous work 9 , the design of the QDs can affect the hybridization strength and hence the efficiency of carrier scattering. Therefore two different QD geometries for the TI devices are considered, one with moderate (16x24nm) and one with near-optimal (16x32nm) hybridization strength.…”

“…In an earlier publication 9 , we discussed the physics of carrier scattering in tunnel injection structures. When the design leads to hybridized states between IW and QD, this significantly enhances the carrier capture into the laser levels.…”

Morphology of wetting-layer states in a simple quantum-dot wetting-layer model

“…8 shows a remarkable agreement with the number variance of the Semi-Poisson statistics in Eq. (19). For L > 6 we observe deviations which might be the generic saturation behavior due to a finite number of energy levels used, see, e.g.…”

“…However, the resulting WL states are still approximated by plane waves, but with local modifications at the position of the QDs. Calculations without the above approximations exist for single QDs [17][18][19], but the considered spatial domain around the QD is small, so the WL states are treated only locally and their properties are not in the focus.…”