Date of Graduation

12-2025

Document Type

Thesis

Degree Name

Master of Science in Materials Engineering (MS)

Degree Level

Graduate

Department

Materials Science & Engineering

Advisor/Mentor

Yu, Shui-Qing

Committee Member

Hu, Jin

Second Committee Member

Kohanek, Julia

Keywords

Aspect Ratio Trapping; CMOS; GeSn; Optoelectronics; Photonics; Semiconductor

Abstract

Silicon (Si) began dominating the electronics industry since 1960s, the dominance came due to its affordability and well developed fabrication processes. But when it comes to light emitting devices and photonics devices in general, the indirect bandgap of Si has caused many scientists to search for alternative semiconductor materials that can deliver better light emission, materials that can also improve wavelengths detection which is also very limited when it comes to Si, reduce losses and greater light amplification, all this while still being affordable. Despite these limitations, Si has been widely used in Complementary Metal Oxide Semiconductor (CMOS) manufacturing and provided low cost and high volume production. Many researchers have opted to go with III-V materials like GaAs and InP as an alternative and more efficient materials to replace Si due to their direct bandgap nature. These III-V materials have proved to be more efficient light emitters. Apart from being more efficient than Si, III-V materials also have drawbacks, they are expensive to fabricate, complicate to integrate with Silicon based ecosystem and they surfer with defects that arise from lattice mismatch. Overtime, these problems have made researchers to actively continuing to search for other alternative materials that can overcome these drawbacks. GeSn was found to be promising candidate to replace III-V, this is because Si, Ge and Sn are all group IV materials in the periodic table which means there is huge possibility that GeSn can be directly and more easily integrated into Si based platform. Since then, GeSn has become more popular among researchers, its bandgap tunability makes it a better candidate to rebuild photonic technology. GeSn alloys is capable to transition from indirect to direct bandgap depends on how much Sn composition, if we have around 8% Sn content, these alloys can transition to direct bandgap materials which is more efficient for light emitting devices. In addition to that, it improves its capabilities across infrared spectrum about 2 microns to 12 microns. This mentioned behavior made researchers to believe GeSn alloy is more favorable for a wide range of modern and future photonics and opto-electronics applications like lasers, detectors and LEDs. The Monolithic integration of Ge₁ₓSnₓ (GeSn) alloys on Si(100) substrates can pave the way for a better, cheaper and more efficient CMOS mid-infrared optoelectronics devices. As always, nothing comes with no cost, since GeSn has different thermal coefficient and larger lattice mismatch of around 4-8% with that of Si, this introduces high dislocations densities and strain relaxation during the epitaxial growth. There are various ways that can be used to address these issues. In this work, the focus turns towards one method which has been very promising and widely used with other materials to address defect problems, this method is called Aspect Ratio Trapping (ART). This method use geometrical defect filtering where a SiO2 layered is deposited on Si substrate and tiny holes are open within the SiO2 layer, these narrow vertical openings are then can be used to confine and essentially block dislocations from continuing to the surface and avoid them from infiltrating the regions where active device functionality is expected to occur. This aims at demonstrating how aspect ratio trapping (ART) can be used to solve one of the biggest problems in materials science, epitaxial growth in GeSn films. This thesis will also focus on building optical setups for aspect ratio trapping (ART) structures characterization and fabrication techniques. Photoluminescence and mirco Photoluminescence were built and used to characterize the performance of GeSn materials grown on aspect ratio trapping structures to study how the material behaves under light excitation with different Sn composition. A laser beam profiling was also used with methods like knife-edge technique to improve the alignment accuracy and power. In Addition to that, this thesis dives deeps into study and explains how dislocation trapping works, and how bandgap properties can be tuned and affect GeSn alloys. Adjusting the materials its techniques used to grow is very important to achieve the needs of specific applications, and can provide useful contributions to both materials and device side of modern and future semiconductor.

Download

Share

COinS