The electronic structure of InAs quantum dots covered with the GaAs 1−y Sb y strain reducing layer has been studied using the k · p theory. We explain previous experimental observations of the red shift of the photoluminescence emission with increasing y and its blue shift with increasing excitation power. For y > 0.19 type-II dots are formed with holes localized in the GaAsSb close to the dot base; two segments at opposite sides of the dot, forming molecular-like states, result from the piezoelectric field. We also propose an experiment that could be used to identify the hole localization using a vertical electric field.

In this work we study theoretically and experimentally the multi-particle structure of the so-called type-II quantum dots with spatially separated electrons and holes. Our calculations based on customarily developed full configuration interaction ap- proach reveal that exciton complexes containing holes interacting with two or more electrons exhibit fairly large antibinding energies. This effect is found to be the hallmark of the type-II confinement. In addition, an approximate self-consistent solution of the multi-exciton problem allows us to explain two pronounced phenomena: the blue-shift of the emission with pumping and the large inhomogeneous spectral broadening, both of those eluding explanation so far. The results are confirmed by detailed intensity and polarization resolved photoluminescence measurements on a number of type-II samples.

The optical response of (InGa)(AsSb)/GaAs quantum dots (QDs) grown on GaP (001) substrates is studied by means of excitation and temperature-dependent photoluminescence (PL), and it is related to their complex electronic structure. Such QDs exhibit concurrently direct and indirect transitions, which allows the swapping of Γ and L quantum confined states in energy, depending on details of their stoichiometry. Based on realistic data on QD structure and composition, derived from high-resolution transmission electron microscopy (HRTEM) measurements, simulations by means of k · p theory are performed. The theoretical prediction of both momentum direct and indirect type-I optical transitions are confirmed by the experiments presented here. Additional investigations by a combination of Raman and photoreflectance spectroscopy show modifications of the hydrostatic strain in the QD layer, depending on the sequential addition of QDs and capping layer. A variation of the excitation density across four orders of magnitude reveals a 50 meV energy blueshift of the QD emission. Our findings suggest that the assignment of the type of transition, based solely by the observation of a blueshift with increased pumping, is insufficient. We propose therefore a more consistent approach based on the analysis of the character of the blueshift evolution with optical pumping, which employs a numerical model based on a semi-self-consistent configuration interaction method.

Detailed theoretical studies of the electronic structure of (InGa)(AsSb)/GaAs/GaP quantum dots are presented. This system is unique since it exhibits concurrently direct and indirect transitions both in real and momentum space and is attractive for applications in quantum information technology, showing advantages as compared to the widely studied (In,Ga)As/GaAs dots. We proceed from the inspection of the confinement potentials for k = 0 and k = 0 conduction and k = 0 valence bands, through the formulation of k · p calculations for k-indirect transitions, up to the excitonic structure of Γ-transitions. Throughout this process we compare the results obtained for dots on both GaP and GaAs substrates, enabling us to make a direct comparison to the (In,Ga)As/GaAs quantum dot system. We also discuss the realization of quantum gates.

We present a detailed investigation of different excitonic states weakly confined in single GaAs/AlGaAs quantum dots obtained by the Al droplet-etching method. For our analysis we make use of temperature-, polarization-and magnetic field-dependent µ-photoluminescence measurements, which allow us to identify different excited states of the quantum dot system. Besides that, we present a comprehensive analysis of g-factors and diamagnetic coefficients of charged and neutral excitonic states in Voigt and Faraday configuration. Supported by theoretical calculations by the Configuration interaction method, we show that the widely used single-particle Zeeman Hamiltonian cannot be used to extract reliable values of the g-factors of the constituent particles from excitonic transition measurements. arXiv:1909.04906v1 [cond-mat.mes-hall]

We show that anisotropic biaxial stress can be used to tune the built-in dipole moment of excitons confined in In(Ga)As quantum dots up to complete erasure of its magnitude and inversion of its sign. We demonstrate that this phenomenon is due to piezoelectricity. We present a model to calculate the applied stress, taking advantage of the so-called piezotronic effect, which produces significant changes in the current-voltage characteristics of the strained diode-membranes containing the quantum dots. Finally, self-consistent k·p calculations reveal that the experimental findings can be only accounted for by the nonlinear piezoelectric effect, whose importance in quantum dot physics has been theoretically recognized although it has proven difficult to single out experimentally.

No abstract