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

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.