자료유형  

 학위논문

Control Number  

0017164804

International Standard Book Number  

9798346389804

Dewey Decimal Classification Number  

540

Main Entry-Personal Name  

Lentz, John Zachary.

Publication, Distribution, etc. (Imprint  

[S.l.] : Stanford University., 2024

Publication, Distribution, etc. (Imprint  

Ann Arbor : ProQuest Dissertations & Theses, 2024

Physical Description  

196 p.

General Note  

Source: Dissertations Abstracts International, Volume: 86-05, Section: A.

General Note  

Advisor: McIntyre, Paul.

Dissertation Note  

Thesis (Ph.D.)--Stanford University, 2024.

Summary, Etc.  

요약Semiconductor nanowires (NWs) are intriguing for the access they provide to fundamental properties as well as their range of potential applications. NWs have shown their merits in enhanced gate control as the channel material for transistors, control and tolerance of strain, including in various heteroepitaxy configurations, tunable optical absorption, and emission and confinement of light, among other areas. In this thesis, I will discuss work on Ge core/Ge-Sn shell nanowires. The Ge-Sn system (GeSn) is interesting primarily because for sufficient metastable Sn concentrations of around 10 at.%, the material attains a direct gap in the midinfrared which is tunable with Sn composition, with only group IV materials, providing opportunities for optoelectronics monolithically integrated on Si. Growing this material as a shell around Ge nanowires has the principal benefit of allowing the GeSn to grow strain-free, encouraging Sn incorporation and suppressing compressive strain in the GeSn which would move the gap back towards indirect character. In this thesis, I will discuss several areas in which we have used such samples for fundamental studies of atomic structure in GeSn and how that structure impacts properties: compositional short-range order (SRO), structure and order as the Sn content varies, and electrically active vacancy-related defects.The first results chapter will consist of a discussion of our work on characterization of SRO in Ge-Sn alloys. Compositional SRO has regained attention recently due to its contribution to exceptional mechanical properties in high entropy alloys. However, theory indicates that SRO may also be present in and affect the optoelectronic properties of Ge-Sn. These calculations indicate that Sn atoms, rather than occupying lattice sites randomly, should repel each other to such an extent that Sn-Sn first nearest neighbor (1NN) pairs are rare. Existing atom probe tomography (APT) characterization shows much less SRO than would be expected based on theory, prompting interest in new characterization methods to shed light on the discrepancy. We characterized SRO in Ge-Sn alloys using synchrotron extended x-ray absorption fine structure (EXAFS) spectroscopy and found that Sn atoms are about 40% less likely to be the 1NN of other Sn atoms relative to a truly random alloy, a result nicely in line with the theory. The detection of SRO is an important first step towards eventual control of SRO for heterostructure applications.Next, a comparative study of EXAFS results between the Ge core/GeSn shell nanowires sample were compared to results from a GeSn film grown by molecular beam epitaxy (MBE). A novel preparation technique was used to pattern the GeSn into ribbons and under etch them to release them from the substrate for the EXAFS measurements. Special attention is paid to results which indicate strong short-range order (SRO) in these GeSn films, even stronger than CVD-grown nanowire samples. Additionally, the presence of longer-range disorder is indicative of the strain present in the film as-grown. The clear existence of SRO in these samples provides evidence that SRO is potentially a more general phenomenon in GeSn and not merely isolated to GeSn NW shells.Since the GeSn band gap is tunable with composition for metastable high Sn contents, trends with composition are especially interesting in this system.

Subject Added Entry-Topical Term  

Crystal structure.

Subject Added Entry-Topical Term  

Tomography.

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Nanowires.

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Gases.

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Single crystals.

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Christianity.

Subject Added Entry-Topical Term  

Chemical vapor deposition.

Subject Added Entry-Topical Term  

Molecular beam epitaxy.

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Point defects.

Subject Added Entry-Topical Term  

Alloys.

Subject Added Entry-Topical Term  

Thin films.

Subject Added Entry-Topical Term  

Annealing.

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Atomic physics.

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Condensed matter physics.

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Materials science.

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Medical imaging.

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Nanotechnology.

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Religion.

Added Entry-Corporate Name  

Stanford University.

Host Item Entry  

Dissertations Abstracts International. 86-05A.

Electronic Location and Access  

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Control Number  

joongbu:656213