New strategies for Ge-on-Si materials and devices using non-conventional hydride chemistries: The tetragermane case

We introduce a practical chemical vapor deposition strategy for next-generation Ge-on-Si epitaxy utilizing recently introduced Ge ₄H₁₀ hydride sources that confer unprecedented deposition efficiencies at very low-temperatures (<400 °C). The corresponding high growth rates produce thick bulk-like Ge films with structural and electrical properties significantly improved relative to state-of-the-art results obtained using conventional approaches. The use of a pure, single-source compound facilitates the control of residual doping, and enables p-i-n devices whose dark currents are not entirely determined by defects and whose zero-bias optical collection efficiencies are higher than obtained from samples fabricated using alternative Ge-on-Si approaches. The reaction pathways leading to the high-yield synthesis of Ge₄H₁₀ are identified on the basis of quantum thermochemistry simulations. The results suggest a simple approach to routine synthesis of tetragermane as the main product in quantities sufficient to be deployed as a commercial source.