Ultra-low-temperature epitaxy of ge-based semiconductors and optoelectronic structures on Si(100): Introducing higher order germanes (Ge ₃H ₈, Ge ₄H ₁₀)

This paper reports the development and optimization of an enhanced process to produce viable quantities of trigermane, and controlled smaller quantities tetragermane, which are isolated as a mixture of perfectly stable isomers. The identity and fundamental structural properties of these higher order germanes (Ge ₃H ₈, and Ge ₄H ₁₀ isomers) are thoroughly characterized using spectroscopic methods and quantum chemical simulations. These hydride products are found to exhibit a remarkably good stability and ease of use, making them compatible with current industry standards. As a proof-of-concept, we demonstrate that Ge ₃H ₈ and Ge ₄H ₁₀ both represent efficient and cost-effective precursors for ultra-low-temperature chemical vapor deposition of pure Ge and GeSn alloy films directly on Si(100) wafers, at conditions compatible with processes currently employed in next-generation group IV device designs. In the case of Ge the crystallinity of the resultant films is found of optical quality, in spite of the extremely low temperature processing, suggesting the potential for rapid adoption of the new processes into the device application arena. In the case of GeSn alloys, the high growth rates achieved at low temperatures (∼300 °C) allow the formation of highly concentrated bulk-like layers with unprecedented thicknesses compatible with Si-based photonic applications such as infrared (IR) emitters and detectors directly on Si wafers.