Yang, Junjie;
(2021)
Monolithic Growth of InAs/GaAs Quantum Dot lasers on Silicon Substrates by Molecular Beam Epitaxy.
Doctoral thesis (Ph.D), UCL (University College London).
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Abstract
Monolithic integration of direct-bandgap III-V materials onto Si is an attractive approach to realise on-chip light sources for Si-based photonic integrated circuits (PICs). However, the direct epitaxy of III-V materials onto Si substrates introduces a high density of crystalline defects such as threading dislocations (TDs), antiphase boundaries (APBs) and micro-cracks, which serve as non-radiative recombination centres and hence significantly degrade the performance of laser devices. This thesis aims to reduce the impact of these critical defects on molecular beam epitaxy (MBE) grown, high-performance InAs/GaAs quantum dot (QD) lasers on Si substrates, and hence to provide practical on-chip light sources for Si-based PICs. A thin Ge buffer layer is first proposed to replace a part of thick GaAs to solve the micro-crack issue while keeping the laser performance unaffected. Ge buffer layers are optimised in terms of annealing methods, thickness and doping materials to obtain low TD density. Based on the optimised Ge/Si virtual substrate, an all-MBE grown InAs/GaAs QD laser device has been demonstrated with an overall thickness (5.4 µm) close to the cracking threshold (~5 µm). Lasing up to 130 °C is obtained for this laser. A novel method has been developed in Chapter 4 to suppress the formation of APBs during the epitaxy of polar III-V on non-polar Si. It enables the monolithic integration of InAs/GaAs QD lasers on microelectronic standard nominal Si (001) substrates. The parallel Si single-atomic-height (S) steps formed on the Si buffer layer reorganise the nucleation of APBs into an ordered distribution and promote sufficient self-annihilation of APBs in the subsequent GaAs growth. Finally, a 1 µm-thick APB-free GaAs grown on Si (001) substrate has been demonstrated. Based on this APB-free GaAs/Si (001) platform, an all-MBE grown high-performance InAs/GaAs QD laser has been fabricated with a low threshold current density (80 A/cm2 ) and a high operating temperature (120 °C). Moreover, studies related to APB nucleation, propagation, and interaction with TDs are presented in Chapter 5, which provides insights for further optimising high-performance InAs/GaAs QD lasers grown on Si (001) substrates.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | Monolithic Growth of InAs/GaAs Quantum Dot lasers on Silicon Substrates by Molecular Beam Epitaxy |
| Event: | UCL (University College London) |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Copyright © The Author 2021. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request. |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Electronic and Electrical Eng |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10136483 |
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