Tensile-strained Germanium via III-V Heterostructures for Emerging Electronic and Photonic Applications

dc.contributor.authorBhattacharya, Shuvodipen
dc.contributor.committeechairHudait, Mantu K.en
dc.contributor.committeememberOrlowski, Mariusz Kriysztofen
dc.contributor.committeememberHeremans, Jean Josephen
dc.contributor.committeememberAsryan, Levon Volodyaen
dc.contributor.committeememberJia, Xiaotingen
dc.contributor.departmentElectrical Engineeringen
dc.date.accessioned2025-06-03T08:00:55Zen
dc.date.available2025-06-03T08:00:55Zen
dc.date.issued2025-06-02en
dc.description.abstractThe relentless scaling down of feature dimensions in silicon (Si)-based complementary metal-oxide-semiconductor (CMOS) architectures has been the primary catalyst for the enhancement of technological functionalities within portable electronic systems and computational infrastructures. Concurrently, advancements in condensed matter physics, materials science, and state-of-the-art fabrication methodologies have collectively facilitated continued improvements in device performance metrics. Nonetheless, as Si and strained-Si-based platforms approach phenomenological saturation thresholds, the pursuit of alternative channel semiconductor materials becomes imperative. Simultaneously, the escalating integration of Si photonics aims to mitigate the performance bottleneck imposed by copper-based electrical interconnects at nanoscale dimensions. In this context, band-engineered germanium (Ge) emerges as a pivotal candidate for propelling next-generation electronic and photonic device paradigms. This study systematically examines unintentionally doped and heavily boron (B)-doped, tensile-strained germanium (ε-Ge), synthesized via III-V metamorphic buffer layers comprising InGaAs and InAlAs. The structural quality and carrier dynamics of such Ge epilayers is characterized with a comprehensive suite of advanced techniques, including transmission electron microscopy (TEM) for defect analysis, high-resolution x-ray diffractometry (HR-XRD) for strain and lattice parameter determination, microwave-reflectance photoconductive decay (μ-PCD) to quantify effective carrier lifetimes τeff, and atomic force microscopy (AFM) for surface morphology assessment. Through iterative refinement of epitaxial growth parameters, defect-limited τeff >100 ns is achieved in unstrained Ge and ε-Ge, with strain levels surpassing the indirect-to-direct bandgap crossover threshold. These findings position ε-Ge as a viable material for photonic device integration. Furthermore, detailed comparative analyses reveal that heteroepitaxial growth on InGaAs templates yields superior crystalline quality compared to InAlAs counterparts, establishing InGaAs as the preferred buffer for ε-Ge integration. The feasibility of integrating overlayers on ε-Ge to mimic quantum well separate confinement heterostructure configurations is demonstrated, enabling the fabrication of Ge-based active optical sources. Notably, for the first time, combined experimental validation and atomistic modeling elucidate that high boron incorporation within highly ε-Ge layers induces an additive tensile strain, which dynamically alters the defect landscape during epitaxial growth. This comprehensive investigation thus advances the fundamental understanding of ε-Ge/III-V heterostructures, equipping device engineers with vital insights for engineering next-generation electronic and photonic systems optimized for scalability, performance, and integration.en
dc.description.abstractgeneralTransistors are essential components in a wide range of electronic devices and computing systems used in modern technology. The ongoing miniaturization of silicon-based complementary metal-oxide-semiconductor (CMOS) transistors over recent decades has played a vital role in achieving significant enhancements in computational performance, supported by parallel developments in solid-state physics, materials science, and manufacturing processes. Furthermore, improved fabrication methods have enabled high-volume, cost-effective production, increasing accessibility for consumers and industries alike. As a result, micro- and nano-electronic devices are now widespread across various sectors, interconnected within the Internet of Things ecosystem, with vast amounts of data being shared and managed by data centers and related infrastructure. However, the continued downscaling of transistors is approaching fundamental physical limitations. As device dimensions shrink, challenges such as increased power density, leakage currents, and heat dissipation become more prominent. Similarly, copper interconnects used for circuitry communication are experiencing performance constraints, with increased signal delay and potential reliability concerns. To sustain the trajectory of ongoing performance improvements, research into alternative materials and innovative solutions is essential. This study systematically examines the material properties and carrier dynamics of epitaxially grown Germanium and tensile strained Germanium using III-V buffers, aiming to advance applications in emerging electronic and photonic devices. Through a comprehensive suite of analytical and modeling methods, the work explores various approaches to fabricating high-quality Germanium epitaxial layers. Additionally, the research demonstrates the potential of heterostructures for developing Germanium-based optical sources, which could serve as viable alternatives to copper interconnects nearing their performance limits. Overall, this work provides valuable insights into these material systems, equipping device engineers with knowledge necessary to continue the advancement of semiconductor device performance.en
dc.description.degreeDoctor of Philosophyen
dc.format.mediumETDen
dc.identifier.othervt_gsexam:44090en
dc.identifier.urihttps://hdl.handle.net/10919/134976en
dc.language.isoenen
dc.publisherVirginia Techen
dc.rightsCreative Commons Attribution 4.0 Internationalen
dc.rights.urihttp://creativecommons.org/licenses/by/4.0/en
dc.subjectMolecular Beam Epitaxyen
dc.subjectGermaniumen
dc.subjectTensile Strainen
dc.subjectHeterogeneous Integrationen
dc.subjectMetamorphic Buffersen
dc.subjectEffective Carrier Lifetimeen
dc.subjectCarrier Dynamicsen
dc.subjectDopingen
dc.subjectMicrowave Reflectance Photoconductance Decayen
dc.titleTensile-strained Germanium via III-V Heterostructures for Emerging Electronic and Photonic Applicationsen
dc.typeDissertationen
thesis.degree.disciplineElectrical Engineeringen
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen
thesis.degree.leveldoctoralen
thesis.degree.nameDoctor of Philosophyen

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