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

Abstract

The 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.