Date of Graduation

8-2022

Document Type

Thesis

Degree Name

Master of Science in Materials Engineering (MS)

Degree Level

Graduate

Department

Materials Science & Engineering

Advisor/Mentor

Yu, Shui-Qing "Fisher"

Committee Member

Salamo, Gregory J.

Second Committee Member

Ware, Morgan E.

Third Committee Member

Leftwich, Matthew B.

Fourth Committee Member

Morgan, Timothy

Keywords

Germanium tin; silicon germanium tin; optoelectrical devices

Abstract

Germanium tin and silicon germanium tin are group IV semiconductor alloys that have gained significant interest in recent years for their potential use in optoelectrical devices. While silicon and germanium are indirect bandgap materials on their own, alloying them with tin in sufficient quantities leads to a transition to direct bandgap alloys. Direct gap performance opens the door for efficient light emitting and detecting devices fabricated entirely on group IV materials that are compatible with the industry standard CMOS manufacturing techniques. Germanium tin and silicon germanium tin have bandgaps that respond to light in the mid to near infrared spectrum which is ideal for night vison technologies. In this thesis two techniques are used to determine the band offsets of GeSn and SiGeSn heterojunctions. X-ray photoelectron spectroscopy is used to directly measure the electron binding energies at the surface of a material and these binding energies are used to determine the relative positions of the valance band maximums. The second technique is internal photon emission which relies on fabricating a photodiode device on a SiGeSn/GeSn sample and measuring the photocurrent. From the photocurrent the potential barrier heights, when photocurrent first starts to flow, can be determined and the band structure and offsets can be determined. Knowing the band structure of semiconductor materials is crucial because the behavior of devices fabricated on these materials will have their performance determined largely by the physics at the material interfaces. Device modeling and prediction is largely reliant on having accurate band structure information. Being able model devices made on these emerging materials will be informative and guide the growth effort to focus on material compositions that are best suited for specific applications.

The sample selection criteria for the x-ray photoelectron spectroscopy and internal photon emission measurements. This will include the sample preparation necessary for the spectroscopy samples as well as the device fabrication process used to make the photodetector device for the internal photon emission measurements. Alternative band offset techniques and their merits and challenges will also be covered. The discussion concludes with an evaluation of the reliability of the measured offsets and how they compare to theoretical values and empirical values from literature. Finally, there will be plans for future work including additional offset measurements that are planned to cover a larger portion of the vast array of material composition combination for these alloys. The future work discussion will also cover the next steps for using the measured offset values for the purpose of device modeling and simulation for the realization of detectors and infrared cameras build on these group IV alloy material systems.

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