Date of Graduation

5-2021

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Microelectronics-Photonics (PhD)

Degree Level

Graduate

Department

Microelectronics-Photonics

Advisor/Mentor

Gregory J. Salamo

Committee Member

Shui-Qing Yu

Second Committee Member

Min Zou

Third Committee Member

Huaxiang Fu

Fourth Committee Member

Rick Wise

Keywords

GeSn, Optoelectronic devices, Semiconductors, X-ray diffraction

Abstract

Germanium-tin alloys with Sn compositions higher than 8 at. % to 10 at. % have recently attracted significant interest as a group IV semiconductor that is ideal for active photonics on a Si substrate. The interest is due to the fact that while at a few percent of Sn, GeSn is an indirect bandgap semiconductor, at about 8 to 10 at. % Sn, GeSn transitions to a direct bandgap semiconductor. This is at first surprising since the solid solubility of Sn in Ge under equilibrium growth conditions is limited to only about 1 at. %. However, under non-equilibrium growth conditions, Sn concentrations in GeSn of more than 20 at. % are reported. At these high concentrations several problems arise due to severe lattice mismatch and chemistry that can have serious impact on the optical quality and stability of GeSn optical devices. As a result, it is important to understand and perhaps control the growth of GeSn semiconductors containing such high Sn concentrations. This requires an investigation of the measurement, interplay, and role of composition, strain, defects, structure, segregation, and precipitation in GeSn/Ge/Si(001) heterostructures and is the subject of this dissertation

More specifically, in this study, the experimental and theoretical x-ray diffraction analysis is shown as a reliable technique for non-destructive and precise characterization of composition, strain, defects, structure, segregation, and precipitation in GeSn. As a result, under an annealing treatment of GeSn/Ge/Si(001) heterostructures, the interplay of these properties was correlated with the stability and optical quality. For example, the density of misfit dislocations of ~2 × 105 cm-1 in the as-grown GeSn layers was shown to be correlated to the onset of Sn segregation. These results provide insight that can be used for the growth of metastable GeSn alloys with improved Sn content, thermal stability, and optical quality.

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