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Identifier

000416931

Title

Μικροκοιλότητες νιτριδίων για πολαριτονικές διατάξεις

Alternative Title

Nitride microcavities for polariton devices

Author

Μίζιου, Φωτεινή Γ.

Thesis advisor

Γεωργακίλας, Αλέξανδρος

Reviewer

Πελεκάνος, Νικόλαος
Χατζόπουλος, Ζαχαρίας

Abstract

In recent years, group III nitride semiconductors have increasingly attracted the attention of the research community in the field of optoelectronics due to their unique properties. More specifically, regarding the fabrication of microcavities that operate in the strong coupling regime, GaN has been found to allow the operation of high‐performance polariton devices at room temperature. In the context of this paper, a series of samples with a different number of GaN/AlGaN polar quantum wells over a c‐axis grown InGaN/GaN layer was designed and grown. In parallel, with a view to restrict the spontaneous and piezoelectric polarization fields which are found in polar structures and affect the performance of c‐plane photonic devices, a nonpolar (m‐plane) sample with the same structure was fabricated. Before any sample treatment is initiated, photoluminescence and reflectance measurements were carried out in order to examine the excitonic properties and crystal quality of polar and non‐polar quantum wells. The ultimate goal was to fabricate free‐standing GaN/AlGaN membranes, having a thickness of ~200nm, corresponding to a 3λ_ο/2n_c structure with λ_ο=360nm and n_c the effective refractive index of the cavity. This was achieved using the method of selective photo‐electrochemical etching for the lateral removal of the InGaN layer. The most important part of this wotk was that non polar membranes were fabricated by this technique. Next, the membranes created were transferred onto dielectric mirrors known as Distributed Bragg Reflectors (DBR), thus forming a half‐microcavity which was completed by placing the dielectric top mirror. In general, rather uniform membranes, properly incorporated into the dielectric mirrors, were observed, despite the fact that, in several cases, the membranes appeared to be strained (curved) upon placement of the dielectric top mirror. In our first effort to understand this behavior, we examined whether the mismatch in coefficients of thermal expansion between GaN and DBR materials affects the membrane curvature. Consequently, in SiO₂/Ta₂O₅ mirror that has been used until recently, SiO₂, with the lowest thermal expansion coefficient compared to other materials, was replaced by Al₂O₃, without any particular improvement achieved. On the other hand, by reducing the temperature of mirror deposition from 300°C to 150°C and the number of periods, the membrane curvature was minimized.

Language

Greek

Subject

Etching

Excitons

Gan

Membranes

Non-polar

Pec

Polaritons

Quantum wells

Εγχάραξη