Type-II GaAs/GaSb Quantum-Ring Light Emitting Diodes for Telecom-Band Emission

Acar Tekin, Gizem and Hayne, Manus (2026) Type-II GaAs/GaSb Quantum-Ring Light Emitting Diodes for Telecom-Band Emission. PhD thesis, Lancaster University.

Text (GAcarTekin_PhD_2025)
GAcarTekin_PhD_2025.pdf - Published Version
Download (5MB)

Abstract

This thesis presents the design, fabrication and experimental characterisation of type-II GaSb/GaAs quantum-ring (QR) light-emitting diode (LED) architectures aimed at enabling future electrically driven single-photon operation at telecommunication wavelengths. Generating high-purity quantum light in the telecom O-band (1260-1360 nm) remains a major challenge for practical quantum communication technologies, and type-II GaSb/GaAs heterostructures offer a promising route due to their reduced strain, strong hole confinement and naturally long-wavelength emission. A series of GaSb/GaAs QR-LEDs were grown by molecular beam epitaxy (MBE), fabricated in multiple geometries, and characterised electrically and optically. Electroluminescence measurements revealed broadband type-II emission between 1.18 and 1.28 μm, current-induced blue-shifts, temperature-induced red-shifts and activation energies of 110-125 meV, consistent with expectations for strongly confined type-II heterostructures. To address the intrinsic extraction bottleneck of semiconductor LEDs, a distributed Bragg transmitter (DBT) was designed by transfer-matrix modelling, grown monolithically as a seven-period GaAs/AlGaAs multilayer, and verified structurally by transmission electron microscopy and ellipsometry. DBT-integrated QR-LEDs exhibited a characteristic spectral modulation consistent with measured and simulated DBT transmission, together with enhanced collected electroluminescence. The strongest relative improvement occurred at low injection, where DBT devices showed up to an order-of-magnitude increase in collected output compared with reference devices, although device-to-device variation prevents this from being interpreted as a definitive absolute extraction-efficiency gain. A cavity-integrated QR-SPLED architecture incorporating a GaAs quantum-dot electron-filter layer and a DBR-defined optical cavity was then realised. Across the full mesa series, these devices exhibited a single cavity-selected O-band line centred near 1.24-1.25 μm, with linewidths remaining stable in the ~10-12 nm range. Under fixed-current operation, the cavity mode remained spectrally robust from 20 °C to 80 °C, while the off-resonant background was systematically suppressed, yielding improved spectral cleanliness at low-to-moderate drive and particularly favourable operation in the 40-80 °C range. Although single-photon statistics were beyond the scope of this thesis, the demonstrated long-wavelength electrical injection, enhanced collected output, cavity-selected emission and thermal stability establish a wafer-scalable platform and define a practical operating window for future telecom-band SPLED implementation. Overall, this work establishes a wafer-scalable platform for long-wavelength, electrically injected quantum-ring emitters and provides the methodology and experimental foundations required for future demonstration of single-photon performance. The insights obtained extend more broadly to type-II semiconductor optoelectronics and cavity-engineered light-emitting devices.