Efficiency limiting processes in epitaxially grown mid-infrared lasers on silicon

Ellis, Aneirin (2025) Efficiency limiting processes in epitaxially grown mid-infrared lasers on silicon. PhD thesis, University of Glasgow.

Abstract

The field of Si photonics is concerned with the development of photonic components that are compatible with highly mature complimentary metal-oxide (CMOS) fabrication processes. Recently, optoelectronic integrated circuits (OEICs) operating in the mid-infrared (mid-IR) have garnered interest, driven by their suitability for lab-on-a-chip spectroscopy. Despite significant progress in passive components, the lack of high-quality CMOS compatible light sources is bottlenecking the production of fully integrated circuits. Various methods of incorporating lasers onto Si exist, however, long-term, monolithic epitaxial growth is preferential for scalable, low-cost manufacturing. In this thesis, two different approaches for epitaxial integration of mid-IR light-sources on Si are investigated.

The first approach is to move away III-V lasers, instead utilising direct bandgap group IV materials. The performance of first-generation electrically injected bulk GeSn lasers were probed using high hydrostatic pressure at low temperature. The devices exhibited threshold current densities of 1.2 kA/cm2 at 85 K which rose with increasing pressure. 93% of the threshold is attributable to large defect related losses in the buffer layer, but even at low temperatures over 1% of carriers are found to occupy states in the L-valley. Temperature-dependent modelling of the carrier distribution was then used to assess the feasibility of GeSn as a bulk active region material. This showed that Sn contents in excess of 20% were required to ensure over 90% of carriers occupy the Γ valley at room temperature (RT). As such, it is likely that the upper operational temperature is limited by indirect carrier losses and a change of heterostructure design is required to achieve electrically injected devices close to RT.

The second approach involves heteroepitaxial growth of mature Sb-based lasers on Si. In this study, devices on Si operating at 2.3 μm are compared to those on native GaSb emitting at a similar wavelength. Temperature-dependent measurements were used to confirm heightened defect related recombination in the devices on Si, and illustrated the onset of a highly temperature dependent process above 150 K. A combination of high hydrostatic pressure measurements and modelling suggest that hole leakage and leakage of carriers to confined L-valley states were likely contributing to the observed temperature dependence in the lasers on Si. Adaptations to the active region and waveguiding layers are proposed to improve the performance of future devices.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: Funding for the project and conference travel provided by the University of Glasgow, the University of Surrey and the Engineering and Physical Sciences Research Council (EPSRC).
• Subjects: T Technology > T Technology (General)
• Colleges/Schools: College of Science and Engineering > School of Engineering > Electronics and Nanoscale Engineering
• Funder's Name: Physical Sciences Research Council (EPSRC)
• Supervisor's Name: Sweeney, Professor Stephen and Georgiev, Professor Vihar
• Date of Award: 2025
• Depositing User: Theses Team
• Unique ID: glathesis:2025-85153
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 05 Jun 2025 07:54
• Last Modified: 05 Jun 2025 07:58
• Thesis DOI: 10.5525/gla.thesis.85153
• URI: https://theses.gla.ac.uk/id/eprint/85153

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