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Identifier

000435921

Title

Πειραματική και θεωρητική διερεύνηση των δομικών και οπτικών ιδιοτήτων των κβαντικών τελειών αρσενικούχου ινδίου ανεπτυγμένων σε υπόστρωμα αρσενικούχου γαλλίου κατά τη (211) κρυσταλλογραφική διεύθυνση

Alternative Title

Experimental and theoretical investigation of structural and optical properties of InAs Quantum Dots grown on (211) gaas substrate

Author

Διαλυνάς, Γεώργιος Εμμ

Thesis advisor

Πελεκάνος, Νικόλαος

Reviewer

Σαββίδης, Παύλος
Χατζόπουλος, Ζαχαρίας
Γεωργακίλας, Αλέξανδρος
Ηλιόπουλος, Ελευθέριος
Κιοσέογλου, Γεώργιος
Κωνσταντινίδης, Γεώργιος

Abstract

Semiconductor Quantum Dots (QDs), based on arsenide (As) heterostructures, are an ideal artificial system to study fundamental properties of matter and the ultimate component of novel promising devices. In case of nanostructures grown on high crystallographic index GaAs substrates, large internal piezoelectric field is expected to exhibit in the nanostructure area. This field is expected to dominate the optical and dynamic properties of nanonstructures. In this work, we present a research concerning the properties of InAs QDs, grown on (211)B GaAs substrate. The structural and morphological properties of (211) InAs dots have been studied in AFM measurements. InAs dots grown on (211)B GaAs substrates have truncated pyramidal shape. The influence of various growth parameters on the size and shape of grown nanostructures has been investigated. With increasing growth temperature the InAs nanostructures increase in size. Similar behaviour is observed with decreasing growth rate as well. AFM measurements also allow the definition of 2-D wetting layer (WL) layer thickness with great accuracy in the range of 1.0 – 1.3 monolayers (MLs) of InAs. The composition of QDs has been investigated in TEM measurements and the variation of In mole fraction throughout QD has been defined. The In mole fraction varies from 30% at the basis of dot to 90% on their top side. In addition to their structural characterization, the optical properties of (211)B InAs QD samples as well as of individual QDs have been studied in photoluminescence (PL) and microphotoluminescence (μ-PL) experiments respectively. The study of PL emission spectra reveal that only a small portion of InAs QDs with height of 2-3nm contribute to the emission spectrum. Study of the emission of individual QDs in μ-PL experiments reveals two prominent features of (211)B InAs QDs. Firstly, having studied the polarization of exciton (X) and biexciton (XX) emission lines in μ-PL experiments, we conclude that the large majority of dots exhibits negligible fine structure splitting (FSS). This fact is attributed to the presence of strong PZ field which increases the symmetry of confinement potential and makes these structures ideal candidates for use in entangled photon applications. Additionally, in contrary to their (100) grown counterparts, (211)Β InAs QDs exhibit large biexciton antibinding energy ΔΕ^bind_XX ( > 10meV). For the interpretation of the experimental results, a theoretical model has been developed that allows the calculation of Χ energies, taking into account many-body effects through the configuration interaction method. The results of these calculations reveal that the antibinding energy of biexcitons is a clear result of the existence of PZ field, predicting that the value of ΔΕ^bind_XX increases with the rise of QD height and of In mole fraction in the dot area and can reach 25meV for InAs/GaAs QDs with 4nm height. The great difference between X and XX emission energies renders these structures as the ideal system for the fabrication of individual photons emitters at high temperatures.

Language

Greek

Subject

Excitons

Fine structure splitting

Indium arsenide(InAs)

Piezoelectric field

Αρσενικούχο Ίνδιο

Διαχωρισμός λεπτής υφής

Εξιτόνια

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