GeSn Thin Film Epitaxy and Quantum Wells for Optoelectronic Devices

Group IV photonics is an effort to generate viable infrared optoelectronic devices using group IV materials. Si-based optoelectronics have received monumental research since Si is the heart of the electronics industry propelling our data driven world. Silicon however, is an indirect material whose optical characteristics are poor compared to other III-IV semiconductors that make up the optoelectronics industry. There have been major efforts to integrate III-V materials onto Si substrates. Great progress on the integration of these III-V materials has occurred but incompatibility with CMOS processing has presented great difficulty in this process becoming a viable and cost-effective solution. Germanium has also been studied and shown to produce direct bandgaps through tensile strain but have limited wavelength coverage. Research into group IV photonics has produced Sn-based materials which have shown promise in achieving efficient infrared optoelectronic devices on Si substrates. The GeSn material has already shown to be direct bandgap with a number of optically active devices already demonstrated. The work presented in this dissertation was focused on the development of ultra-high vacuum chemical vapor deposition of epitaxially grown high optical quality GeSn material. Low temperature Ge and dilute GeSn films were grown directly on Si. Development of Ge buffers on Si for high optical quality GeSn was also accomplished. Growth of GeSn on Ge buffers started under a Sn over-pressure condition. Reduction of the SnCl4 molar flow fraction led to high quality optical material. Material and optical characterization were carried out using x-ray diffraction, transmission electron microscopy, photoluminescence and other methods to determine the Sn composition and optical and material qualites. Additionally, GeSn and SiGeSn barriered GeSn quantum wells grown using a commercial reduced pressure chemical vapor deposition chamber were characterized. The structures were grown on Ge and GeSn buffered Si with up to 9.5% Sn in the buffer. The bandstructure was simulated and compared against optical characterization to verify the simulation results and estimate the carrier confinement in the structures. Increasing the Sn in the GeSn buffer puts more Sn in the well, and wide wells provide enhanced confinement, suggesting a route toward efficient mid-infrared emitters