Improved telecom laser photonics : investigating confinement effects within InxGa1-xAs/GaSb/GaAs quantum ring-in-well structures

Redman, Christopher and Young, Robert (2025) Improved telecom laser photonics : investigating confinement effects within InxGa1-xAs/GaSb/GaAs quantum ring-in-well structures. PhD thesis, Lancaster University.

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Abstract

This project aims to develop high performance III-V gain media used for siliconintegrated near-infra-red (NIR) lasers with efficient light coupling. Molecular beam epitaxy (MBE) was used to successfully create advanced GaSb quantum ring (QR) materials operating in the telecommunication O-band near room temperature (RT). These structures were the focus of an opto-thermal study and were complimented with simulations to probe and understand the underlying carrier recombination mechanisms. A series of GaSb/GaAs quantum ring-in-well (RWELL) structures were grown, with a change in width of the dilute In0.06Ga0.94As quantum wells (QWs), using a novel QR formation technique involving in-situ annealing. The structures were characterised with atomic force microscopy (AFM) and photoluminescence (PL) measurements. Power sweeps were performed on each sample within a range of 0.07 mW to 260 mW. Temperature sweeps were performed from 4.2 K to almost RT. Both temperature and power varied linewidth, emission energy and intensity were studied as a function of QW width. The temperature-dependent analysis, simulations, and study of electron confinement are to the best of our knowledge, performed for the first time. The RWELL gain media were found to have higher activation energies, and therefore greater thermal efficiencies at low temperature (LT), than standard GaSb/GaAs QRs. The activation energies reduce with QW width to a value no less than standard GaSb/GaAs QRs. It was concluded that the wavefunction overlap of the carriers plays a big role in the quenching of PL at 4 K. Strong confinement of the electrons increases the Coulomb energy, oscillator strengths and binding energies, hence expected to provide stable PL at RT. Further optimisations of the growth parameters are still required for the RWELL structures to outperform the reference sample at high temperature (HT). The samples characteristically blueshift with excitation power, demonstrating their type-II band alignment. The rate of blueshift is found to have a dependence on the QW width, and therefore the electron localisation.