Equipment, Techniques and Growth of Ultra-High Purity Aluminum Gallium Arsenide-Gallium Arsenide Heterostructures by Molecular Beam Epitaxy
Abstract
Ultra-high purity aluminum gallium arsenide (AlGaAs)-gallium arsenide (GaAs) heterostructures grown by molecular beam epitaxy (MBE) that host a two-dimensional electron gas (2DEG) are a rich environment for the study of fundamental condensed matter physics and may have applications for quantum computing. This manuscript details research and investigation into critical equipment and materials engineering issues related to the quality of the fabricated 2DEG systems. The MBE technique has proven essential for the fabrication of ultra-high purity and high quality material. The purity of gallium is demonstrated to play a critical role in the quality of the 2DEG. This dissertation begins with an introduction and overview of 2DEG and how mobility, defined as μ=σ/eηe where σ is the conductivity, e is the charge of the electron and η is the density of electrons, can be a useful measure of quality. The ability to use 2DEGs to explore material properties, apply 2DEGs for new applications and use 2DEGs to study fundamental physics motivates the research and the material system. GaAs-AlGaAs semiconductors and heterostructures are reviewed. The finer nuances and techniques of MBE and the growth of ultra-high purity AlGaAs heterostructures, in which high-quality 2DEGs reside will be covered in chapters two and three, respectively. The role of source material purity in 2DEG mobility is demonstrated by testing two different Ga sources concurrently. The effect of alloy disorder on 2DEG quality by growth and electrical characterization of modulation-doped Al0.24Ga0.76As/AlxGa 1-xAs/Al0.24Ga0.76As quantum wells with mole fractions as low as x=0.00057 is reported. Finally, chapter four presents different applications for high-quality 2DEGs, such as a novel FET device free of doping, artificial graphene, switch matrices and control architecture for quantum computing, and the spin qubits which can be created.
Degree
Ph.D.
Advisors
Manfra, Purdue University.
Subject Area
Physics|Materials science
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