Date of Graduation

8-2024

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Materials Science & Engineering (PhD)

Degree Level

Graduate

Department

Materials Science & Engineering

Advisor/Mentor

Salamo, Gregory J.

Committee Member

Yu, Shui-Qing "Fisher"

Second Committee Member

El-Ghazaly, Samir M.

Third Committee Member

Naseem, Hameed A.

Fourth Committee Member

Ware, Morgan E.

Keywords

Algorithm-based GeSn growth; GeSn; Logarithmic-based GeSn growth

Abstract

This dissertation explores the advancement of germanium-tin (GeSn) as a tuneable narrow bandgap material, crucial for the development of high-efficiency photodetectors and laser devices in near- and mid-infrared technologies. We investigate the synthesis challenges, particularly the lattice mismatch between GeSn alloys and substrates, which significantly affects their crystalline and optical qualities. Through molecular beam epitaxy, we examine the growth of Ge and GeSn on GaAs (001) substrates, employing Ge/GaAs and Ge/AlAs buffer layers to investigate these challenges. Our findings, characterized by X-ray diffraction, atomic force microscopy, reflection high-energy electron diffraction, and photoluminescence, demonstrate the production of high-quality Ge layers, achieving atomic steps and photoluminescence comparable to bulk Ge at growth temperatures between 500–600 °C. Subsequently, we grew GeSn films using a Sn compositional exponentially changing gradients and a substrate gradient approach to achieve films with 8 to 10 % Sn composition. Additionally, we introduce a novel algorithmic approach to control the Sn cell temperature logarithmically, allowing us to target and achieve linearly graded Ge1-xSnx compositions. One of such linear Ge1-xSnx gradient growths achieved a pseudomorphic graded composition up to 10 % before a partial relaxation gradient up to 16 %. The combination of experimental and algorithm-driven methodologies not only advances the understanding of GeSn film growth but also marks a major step forward in the synthesis of high-composition, and high-quality GeSn films. This work signifies the first demonstration of algorithmically driven, linearly graded GeSn films in the world, showcasing an advancement in the field of semiconductor technology.

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