Development of Nanostructured Light Emitters in Gallium Nitride

Nanostructured light emitters in gallium nitride (GaN), including quantum wells (QWs) and quantum dots (QDs), are of widespread importance as the key technology enabling high- brightness blue light-emitting diodes (LEDs) and lasers. GaN-based QDs also show promise as novel polarised single-photon sources that can operate at room temperature. This thesis explores methods of structural and optical characterisation of such nanostructures using electron microscopy and in-situ cathodoluminescence, resolving structural features that correlate with cathodoluminescence images, and providing insight into the differences between QD samples grown by quasi-two-temperature and modified droplet epitaxy methods. Refractive index engineering of GaN via the manufacture of porous structures is explored, and the integration of InGaN QWs with porous distributed Bragg reflectors (DBRs) is reported, with a corresponding increase in LED efficiency owing to improved light extraction. Porous DBRs are also integrated with InGaN QDs to create prototype optical cavity structures, combined with a vertical etching process to create nano- and micropillar cavities. Improved light extraction and background suppression from InGaN QDs embedded in such structures is seen, giving a single-photon emission purity of 96%, a record for these QDs. The integration of InGaN QDs into vertical and planar contact geometries also enables the investigation of the behaviour of these QDs under applied electric fields. Finally, the engineering of a full LED structure containing InGaN QDs is reported, leading to the first measurement of electroluminescence from InGaN QDs and the demonstration of electrically- excited single photon emission from this system.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2022

Author dc:creator

• Jarman, John

Advisor dc:contributor.advisor

• Oliver, Rachel

• GaN
• InGaN
• LED
• single photon sources
• optical microcavities
• cathodoluminescence

Licence

• https://creativecommons.org/licenses/by/4.0/

Language dc:language

eng

DOI dc:identifier.doi

https://doi.org/10.17863/CAM.92494

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/345068