Impact of size, shape and composition on piezoelectric effects and the electronic properties of InGaAs/GaAs quantum dots

The strain fields in and around self-organized In(Ga)As/GaAs quantum dots (QD) sensitively depend on QD geometry, average InGaAs composition and the In/Ga distribution profile. Piezoelectric fields of varying size are one result of these strain fields. We study systematically a large variety of realistic QD geometries and composition profiles, and calculate the linear and quadratic parts of the piezoelectric field. The balance of the two orders depends strongly on the QD shape and composition. For pyramidal InAs QDs with sharp interfaces a strong dominance of the second order fields is found. Upon annealing the first order terms become dominant, resulting in a reordering of the electron p- and d-states and a reorientation of the hole wavefunctions

Twofold gain enhancement by elongation of QDs in polarization preserving QD-SOAs

The impact of quantum dot (QD) elongation on key parameters of QD-based semiconductor optical amplifiers (SOAs) is investigated using a combination of 8-band k·p-theory including strain and piezoelectricity up to second order and a rate equation model describing the population of QD ground, excited and wetting layer states. By considering columnar QDs of selected aspect ratios, we show that chip gain and saturation gain can be enhanced by up to +3.6 dB via an increased elongation of the individual QDs while retaining polarization preserving amplification and gain recovery times below 700 fs. Our results enable the optimization of polarization preserving QD-SOA devices which combine ultrafast gain recovery with high gain and low power consumption.DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, Bauelement

Modeling electronic and optical properties of III-V quantum dots – selected recent developments

Electronic properties of selected quantum dot (QD) systems are surveyed based on the multi-band k·p method, which we benchmark by direct comparison to the empirical tight-binding algorithm, and we also discuss the newly developed “linear combination of quantum dot orbitals” method. Furthermore, we focus on two major complexes: First, the role of antimony incorporation in InGaAs/GaAs submonolayer QDs and In1−xGax AsySb1−y/GaP QDs, and second, the theory of QD-based quantum cascade lasers and the related prospect of room temperature lasing.TU Berlin, Open-Access-Mittel - 2022EC/H2020/956548/EU/Quantum Semiconductor Technologies Exploiting Antimony/QUANTIMONYEC/H2020/731473/EU/QuantERA ERA-NET Cofund in Quantum Technologies/QuantER

Electron localization by self-assembled GaSb/GaAs quantum dots.

We have studied the photoluminescence from type-II GaSb/GaAs self-assembled quantum dots in magnetic fields up to 50 T. Our results show that at low laser power, electrons are more weakly bound to the dots than to the wetting layer, but that at high laser power, the situation is reversed. We attribute this effect to an enhanced Coulomb interaction between a single electron and dots that are multiply charged with holes

From k·p to atomic calculations applied to semiconductor heterostructures

International audienceWe present a brief overview of the main results obtained in our group for the simulation of electronic and optical properties of semiconductor heterostructures. A short introduction is given on InAs quantum dots, grown on InP, GaAs and GaP substrates. It is shown that 1-band k·p calculations can be used in the reciprocal space, in order to get a simulation of perfectly ordered array of quantum dots. A semianalytical modeling is also presented, including an axial approximation of the 8*8 band k·p calculations. Linear and nonlinear contributions to piezoelectricity are discussed. A complete 8*8 band k·p approach is then used to show the properties of InAs/InP quantum dots, with different substrate orientations. Finally, a study of the highly strained InAs/GaP interface is performed with a first principle modeling using ABINIT packages. Band lineups and evolution of gap energies are calculated, and compared to those found by Chuang et al. [1

Tuning the Emission Directionality of Stacked Quantum Dots

The emission directionality of stacks of coupled quantum dots (QDs) is investigated within the framework of 8-band k·p-theory including strain and strain-induced piezoelectricity up to second order. Using an artificial cuboidal QD, we show that the degree of radiation anisotropy can be tuned from −33% to nearly +60% via the structure’s vertical aspect ratio. We then demonstrate that these findings can be transferred to stacked InGaAs QDs whose emission directionality is tailored (i) via the interdot coupling strength given by the separating barrier width and (ii) the number of stacked QDs. Our results enable the design and optimization of top and edge emitters based on stacked QDs.DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, Bauelement