Towards a GaN-on-sapphire photonic integrated circuit via micro-transfer printing

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dc.contributor.advisorCorbett, Brian
dc.contributor.advisorPeters, Frank H.
dc.contributor.authorO'Brien, Meganen
dc.contributor.funderScience Foundation Irelanden
dc.date.accessioned2024-09-17T11:05:23Z
dc.date.available2024-09-17T11:05:23Z
dc.date.issued2024en
dc.date.submitted2024
dc.description.abstractPhotonic integrated circuits (PICs) can alleviate the pressure on existing infrastructure for increasing bandwidth requirements by potentially offering faster data transmission with low energy consumption all on the same chip. The ability to integrate active lasing sources to waveguide platforms while also maintaining low-loss coupling is key for efficient PICs.This research focuses on the development of an AlGaN/GaN-on-sapphire platform and the integration of 1.3 µm edge-emitting InP-based multi-quantum well (MQW) and GaAs-based quantum dot (QD) lasing devices to the platform via micro transfer printing (µTP). Gallium nitride (GaN) can be used alternatively to traditional Si-based photonics due to its broad spectral transmission, birefringence, refractive index suitable for fiber coupling, and the possession of both the linear electro-optic effect and non-linear properties. First, we design an AlGaN/GaN structure that creates a single-mode, broad passive spot size for relaxed alignment tolerance of the transfer-printable laser-to-waveguide. Coupling losses as low as 0.6 dB were calculated for the optimal positioning of the laser. We also outline a double-tapered mode adapter that converts the dimensions to more suitable structures for light-routing. The integration of LiNbO3 coupon to the AlGaN/GaN platform is explored through simulations in order to enhance the electro-optic property, and a Mach-Zehnder modulator (MZM) design is proposed. Additionally, the simulations of (i) directional couplers, (ii) polarization converters and (iii) grating couplers on an AlGaN/GaN platform are presented in this work. Next, the fabrication of AlGaN/GaN waveguides devices through BCl3-based etching recipes, along with the challenges of achieving smooth and vertical waveguide sidewalls, are discussed. A BCl3 dry etch for forming a trench into sapphire is also developed for µTP alignment purposes. The AlGaN/GaN waveguides were then characterized, and we distinguish the differences in propagation losses between the TE and TM polarizations.The average propagation losses ranged between 2.4-14.7 dB/cm for both polarizations. Following on from this, both the InP-based MQW and the GaAs-based QD laser coupons were characterized and transfer-printed and coupled to the fabricated GaN waveguides. A coupling output of 2.3 mW at 80 mA was achieved for the QD laser, giving a coupling efficiency of 10.3 %. The results show promise for GaN to be a suitable platform for integrated photonics.en
dc.description.statusNot peer revieweden
dc.description.versionAccepted Versionen
dc.format.mimetypeapplication/pdfen
dc.identifier.citationO'Brien, M. R. 2024. Towards a GaN-on-sapphire photonic integrated circuit via micro-transfer printing. PhD Thesis, University College Cork.
dc.identifier.endpage150
dc.identifier.urihttps://hdl.handle.net/10468/16377
dc.language.isoenen
dc.publisherUniversity College Corken
dc.rights© 2024, Megan O'Brien.
dc.rights.urihttps://creativecommons.org/licenses/by/4.0/
dc.subjectPhotonics
dc.subjectIntegrated photonics
dc.subjectHeterogenenous integration
dc.subjectMicro-transfer printing
dc.subjectGallium nitride
dc.subjectSapphire
dc.subjectPhotonic integrated circuits
dc.subjectQuantum dot lasers
dc.titleTowards a GaN-on-sapphire photonic integrated circuit via micro-transfer printingen
dc.typeDoctoral thesisen
dc.type.qualificationlevelDoctoral
dc.type.qualificationnamePhD - Doctor of Philosophyen
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