Date of Graduation

5-2019

Document Type

Thesis

Degree Name

Master of Science in Microelectronics-Photonics (MS)

Degree Level

Graduate

Department

Microelectronics-Photonics

Advisor/Mentor

Shui-Qing Yu

Committee Member

Gregory Salamo

Second Committee Member

Hameed Naseem

Third Committee Member

Rick Wise

Keywords

Chemical vapor deposition, Germanium tin, Silicon germanium, silicon on sapphire epitaxy, Silicon photonics

Abstract

The development of new materials for efficient optoelectronic devices from Group IV elements is the heart of Group IV photonics. This has direct ties to modern technology as the foundation for the electronics industry is silicon. This has driven the development of silicon-based optoelectronics using these other Group IV materials as silicon is a poor optical material due to its indirect band gap when compared to the III-V semiconductors that are used by most of the optoelectronics industry. While efforts have been made to integrate III-V materials onto silicon substrates, the incompatibility with the complementary metal oxide semiconductor process has limited the viability of this due to the high cost associated with the integration. Germanium has shown potential to be a suitable candidate for possible use though the wavelength range that can be covered is limited as it produces direct bandgaps under tensile strain. Tin-based group IV alloys have been studied and have promising potential in achieving high efficiency optoelectronic devices integrated on silicon. Alloys of germanium-tin have produced many direct bandgap optical devices that have demonstrated the potential for this system. Silicon-germanium-tin alloys hold promise for further expansion of group IV photonics by allowing bandgap and lattice tunability for more complicated device structures and material integrations.

The work presented in this thesis was focused on the critical technologies used to develop these materials using ultra-high vacuum chemical vapor deposition for the epitaxial deposition of films with high optical material qualities. Germanium films were grown at low temperature as well as germanium-tin alloys with highly diluted gas ratios directly on silicon substrates. The germanium films served as buffer layers onto which high quality germanium-tin was deposited using silicon substrates. The growth conditions for the geranium-tin alloys began with a high flow fraction of tin (IV) chloride. The flow fraction of tin (IV) chloride was reduced which led to an improvement in material quality. By using x-ray diffraction, photoluminescence, and other characterization tools material and optical qualities could be determined. This work additionally looked at the initial phase of development of silicon-germanium towards a rhombohedral crystal phase using sapphire substrates.

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