Limiting behaviors in molecular beam epitaxy: from source cell non-idealities to growth condition sensitivity of dilute bismuthides
Date
2025
Authors
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Publisher
University of Delaware
Abstract
The advancement of semiconductor technology increasingly depends on materials with precisely controlled properties and compositions. Among these, dilute bismuthides represent a promising yet challenging class of materials, where small amounts of bismuth dramatically modify the electronic structure of traditional III-V semiconductors. However, their development is hindered by stringent growth requirements and persistent reproducibility challenges. These challenges extend beyond typical material-specific considerations into instrumental limitations. ☐ This dissertation examines two fundamental limitations in molecular beam epitaxy (MBE) growth control through systematic investigation of source cell behavior and bismuthide growth optimization. First, we present a comprehensive study of commonly overlooked non-idealities in source cell operation - including hysteretic and non-hysteretic, history-dependent flux variation, spontaneous flux shifts, and others - that fundamentally limit growth reproducibility. These effects, while present in all MBE growth, become critical contributions when growing sensitive materials – including InAlBiAs, a non-natively lattice matched, quaternary dilute bismuthide. We develop novel calibration methods and operational guidelines to mitigate these limitations. ☐ Second, we study the growth window of InAlBiAs, mapping the complex interdependence of growth conditions, bismuth incorporation, and surface morphology.This investigation reveals a narrow growth window bounded by competing kinetic processes, which enables the study of native electrical properties of high-quality films. By developing a better understanding of induced strain, we achieve lattice-matched InAlBiAs films–a critical step toward practical device applications. ☐ Together, these studies provide new insights into the fundamental challenges limiting MBE growth control while establishing practical guidelines for growing emerging materials with stringent requirements. The findings have broad implications for the development of next-generation semiconductor devices and highlight the need to consider both equipment-level and material-specific limitations when growing novel materials. ☐ To fully explore these challenges in modern epitaxial growth, this dissertation begins with Chapter 1’s examination of relevant background on deposition techniques and semiconductor materials. Emphasis is placed on MBE and dilute bismuthides through in-depth discussion on growth thermodynamics and kinetics as relevant to dilute bismuthides. ☐ Chapter 2 describes the theory of various in situ and ex situ characterization techniques and their practical implementation throughout the remaining chapters. ☐ Chapter 3 studies the reproducibility and limitations of source cell behavior across liquid source cells, valved source cells, and filament source cells. It demonstrates several key physical phenomena related to source fluxes that could limit reproducibility and hinder interpretation of experimental results from certain sensitive materials (like dilute bismuthides). It additionally presents improved control strategies to mitigate the impact of the established effect. ☐ Chapter 4 studies the growth window of InAlBiAs and the inherent sensitivity of bismuth incorporation and surface morphology to non-ideal growth conditions. Additionally, it further explores InAlBiAs grown within the optimized growth window through characterization of native electrical properties and strain states of the films. As a proof-of-concept, it demonstrates how this new understanding of InAlBiAs can be used to grow lattice-matched material, enabling the future development of thick device structures without risk of dislocation nucleation.
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Keywords
Molecular beam epitaxy, Dilute bismuthides, Semiconductor technology