Strategies for the Alignment of Electronic States in Quantum-Dot Tunnel-Injection Lasers and Their Influence on the Emission Dynamics

Tunnel injection (TI) lasers are an appealing concept for the next generation of
semiconductor lasers, as they promise improved modulation rates and better temperature stability.
Moreover, they eliminate a major detrimental effect of quantum dot (QDs) lasers,
which is the gain nonlinearity caused by hot carriers.
In QD-TI lasers, the excited charge carriers are efficiently
captured from the bulk states via an injector quantum well and then transferred
into the QDs via a tunnel barrier.
The introduction of a tunnel barrier for controlling
the coupling of QDs to an injector quantum well (QW) introduces significant
design changes in comparison to conventional QD or QW lasers. As a result,
nanoscale physics and quantum mechanical interaction processes take a more important
role in the device properties.
The alignment of the electronic levels
is crucial for the high efficiency of these processes and especially for the fast
modulation dynamics of these lasers. In particular, the quantum mechanical nature
of the tunneling process must be taken into account in the transition from two-dimensional
quantum well states to zero-dimensional quantum dot states. This results in hybrid states,
from which the scattering into the QD ground states takes place. We combine
electronic state calculations of the tunnel-injection structures with many-body
calculations of the scattering processes and insert this into a complete laser simulator.
This allows us to study the influence of the level alignment and limitations due to
inhomogeneous quantum-dot distributions. We find that the optimal alignment deviates
from a simple picture in which the of the quantum-dot ground state energies are one
LO-phonon energy below the injector quantum well ground state.

We present [1] a theoretical study
of dynamical laser properties inclusing the transport within the device and show the
impact of alignment between the injector quantum well and the QDs on the laser switch-on
process and modulation properties. These are important for the use of these laser
systems in novel telecommunication applications.

[1] arXiv:2402.18165