Dependence of the electronic structure of self-assembled InGaAs/GaAs quantum dots on height and composition

While electronic and spectroscopic properties of self-assembled In_{1-x}Ga_{x}As/GaAs dots depend on their shape, height and alloy compositions, these characteristics are often not known accurately from experiment. This creates a difficulty in comparing measured electronic and spectroscopic properties with calculated ones. Since simplified theoretical models (effective mass, k.p, parabolic models) do not fully convey the effects of shape, size and composition on the electronic and spectroscopic properties, we offer to bridge the gap by providing accurately calculated results as a function of the dot height and composition. Prominent results are the following. (i) Regardless of height and composition, the electron levels form shells of nearly degenerate states. In contrast, the hole levels form shells only in flat dots and near the highest hole level (HOMO). (ii) In alloy dots, the electrons' ``s-p'' splitting depends weakly on height, while the ``p-p'' splitting depends non-monotonically. In non-alloyed InAs/GaAs dots, both these splittings depend weakly on height. For holes in alloy dots, the ``s-p'' splitting decreases with increasing height, whereas the ``p-p'' splitting remains nearly unchaged. Shallow, non-alloyed dots have a ``s-p'' splitting of nearly the same magnitude, whereas the ``p-p'' splitting is larger. (iii) As height increases, the ``s'' and ``p'' character of the wavefunction of the HOMO becomes mixed, and so does the heavy- and light-hole character. (iv) In alloy dots, low-lying hole states are localized inside the dot. Remarkably, in non-alloyed InAs/GaAs dots these states become localized at the interface as height increases. This localization is driven by the biaxial strain present in the nanostructure.Comment: 14 pages, 12 figure

Electronic phase diagrams of carriers in self-assembled InAs/GaAs quantum dots: violation of Hund's rule and the Aufbau principle for holes

We study the orbital and spin configurations of up to six electrons or holes charged into self-assembled InAs/GaAs quantum dots via single-particle pseudopotential and many-particle configuration interaction method. We find that while the charging of {\it electrons} follows both Hund's rule and the Aufbau principle, the charging of {\it holes} follows a non-trivial charging pattern which violates both the Aufbau principle and Hund's rule, and is robust against the details of the quantum dot size. The predicted hole charging sequence offers a new interpretation of recent charging experiments

Electric field control and optical signature of entanglement in quantum dot molecules

The degree of entanglement of an electron with a hole in a vertically coupled self-assembled dot molecule is shown to be tunable by an external electric field. Using atomistic pseudopotential calculations followed by a configuration interaction many-body treatment of correlations, we calculate the electronic states, degree of entanglement and optical absorption. We offer a novel way to spectroscopically detect the magnitude of electric field needed to maximize the entanglement.Comment: 4 pages, 6 figure

Trans-arterial embolisation therapies for unresectable intrahepatic cholangiocarcinoma: A systematic review

Background: Unresectable intrahepatic cholangiocarcinoma (ICC) portends a poor prognosis despite standard systemic treatments which confer minimal survival benefits and significant adverse effects. This study aimed to assess clinical outcomes, complications and prognostic factors of TAE therapies using chemotherapeutic agents or radiation. Methods: A literature search and article acquisition was conducted on PubMed (MEDLINE), OVID (MEDLINE) and EBSCOhost (EMBASE). Original articles published after January 2000 on trans-arterial therapies for unresectable ICC were selected using strict eligibility criteria. Radiological response, overall survival, progression-free survival, safety profile, and prognostic factors for overall survival were assessed. Quality appraisal and data tabulation were performed using pre-determined forms. Results were synthesized by narrative review and quantitative analysis. Results: Twenty articles were included (n=929 patients). Thirty three percent of patients presented with extrahepatic metastases. After treatment, the average rate of complete and partial radiological response was 10% and 22.2%, respectively. Overall median survival time was 12.4 months with a median 30-day mortality and 1-year survival rate of 0.6% and 53%, respectively. Acute treatment toxicity (within 30 days) was reported in 34.9% of patients, of which 64.3% were mild to moderate in severity. The most common clinical toxicities were abdominal pain, nausea and vomiting, and fatigue. Multiplicity, localization and vascularity of the tumor may predict worse overall survival. Conclusions: Trans-arterial therapies are safe and effective treatment options which should be considered routinely for unresectable ICC. Consistent and standardized methodology and data collection is required to facilitate a meta-analysis. Randomized controlled trials will be valuable in the future

Influence of the charge carrier tunneling processes on the recombination dynamics in single lateral quantum dot molecules

We report on the charge carrier dynamics in single lateral quantum dot molecules and the effect of an applied electric field on the molecular states. Controllable electron tunneling manifests itself in a deviation from the typical excitonic decay behavior which is strongly influenced by the tuning electric field and inter-molecular Coulomb energies. A rate equation model is developed to gain more insight into the charge transfer and tunneling mechanisms. Non-resonant (phonon-mediated) electron tunneling which changes the molecular exciton character from direct to indirect, and vice versa, is found to be the dominant tunable decay mechanism of excitons besides radiative recombination.Comment: 4 pages, 4 figure

Carrier relaxation mechanisms in self-assembled (In,Ga)As/GaAs quantum dots: Efficient P -> S Auger relaxation of electrons

We calculate the P-shell--to-S-shell decay lifetime \tau(P->S) of electrons in lens-shaped self-assembled (In,Ga)As/GaAs dots due to Auger electron-hole scattering within an atomistic pseudopotential-based approach. We find that this relaxation mechanism leads to fast decay of \tau(P->S)~1-7 ps for dots of different sizes. Our calculated Auger-type P-shell--to-S-shell decay lifetimes \tau(P->S) compare well to data in (In,Ga)As/GaAs dots, showing that as long as holes are present there is no need for an alternative polaron mechanism.Comment: Version published in Phys. Rev.