PhD Thesis Proposal: Shangda Li

Optional ZOOM LINK

"Defect and Phase Engineering towards Integrated Group-IV Quantum and Photonic Materials on Si"

Abstract

Group-IV alloys have emerged as a compelling material platform for short-to-mid-infrared photonics and advanced CMOS-compatible electronics. Among group-IV materials, germanium-tin (GeSn) semiconductors offer the unique combination of tunable bandgap, high carrier mobility, and compatibility with silicon (Si)-based fabrication processes. These attributes make GeSn a promising candidate for realizing monolithically integrated photodetectors, light sources and modulators on Si. Additionally, Sn-rich GeSn can transform into unique topological phases, exhibiting excellent characteristics such as large magnetoresistance and high quantum mobility, which makes it a promising material for spintronics application. However, realizing high-quality GeSn layers on Si remains challenging due to lattice mismatch, low Sn solubility in Ge, and sensitivity to thermal processing. Moreover, growing α-Sn, a rare elemental material that shows multiple topological phases, on Si, has been limited by exotic substrates or minimal thickness, hindered by even larger lattice mismatch and thermodynamic constraints. This thesis is proposed to address these material challenges using novel synthesis and integration strategies in defect engineering and phase control.

Herein, I propose a systematic investigation into the growth, crystallization, and characterization of semiconductor phase GeSn and topological phase α-Sn on Si. I will first explore novel approaches to achieving high-quality direct epitaxy of Ge and GeSn on Si. The dislocation density is expected to be reduced for Ge-on-Si heteroepitaxy by a nanodot templating method. Second, I will investigate the crystallization dynamics of ion-implanted GeSn layers, combining rapid thermal and laser annealing with spectroscopic and diffraction techniques to assess strain, crystallinity, and Sn diffusion pathways. I will also examine the crystallization of polycrystalline GeSn on Si. Towards the integration of topological materials on Si, the thickness dependence of α-Sn purity and the achievement of phase-pure α-Sn will be described, followed by the preliminary study and outlook of scalability of α-Sn integration on Si.

The proposed work aims to advance CMOS-compatible fabrication of high-performance group-IV optoelectronic and quantum materials. The outcomes would support scalable integration of GeSn-based transistors and light detecting and emitting devices, as well as enable experimental access to topological properties in α-Sn, potentially paving the way for novel quantum device applications.

Thesis Committee

• Jifeng Liu (Chair)
• Eric R. Fossum
• William Scheideler

Contact

For more information, contact Thayer Registrar at thayer.registrar@dartmouth.edu.