Wafer-scale mono-crystalline GeSn alloy on Ge by sputtering and solid phase epitaxy

Abstract

Germanium-tin (GeSn) alloys are of great interest for electronic as well as photonic applications, and their integration on a group-IV (Si or Ge) platform. This letter describes a low deposition temperature, process integration-friendly, high throughput and low cost approach for growing device-quality GeSn epilayers on Ge substrates. Mono-crystalline, wafer-scale GeSn alloy with 3.4% Sn content was grown on Ge (100) substrates by sputtering an amorphous GeSn layer followed by solid phase epitaxy (SPE) at 550 degrees C. Deposition of amorphous layers at room temperature enables incorporation of high bulk Sn content in GeSn epilayers. SPE of the amorphous layer at 550 degrees C leads to a strained, high quality GeSn epilayer having a low full width half maximum of 0.12 degrees, root mean square surface roughness of 0.3 nm and a good GeSn/Ge interface as confirmed through extensive x-ray diffraction measurements, atomic force microscopy and transmission electron microscopy imaging. Additionally, an SiO2 capping layer employed during SPE is shown to prevent Sn out-diffusion and segregation at the surface. To examine electrical properties for potential applications of the GeSn/n-Ge heterostructure, metal/GeSn/n-Ge vertical contact diodes and metal/GeSn circular transfer length method contact structures were fabricated and electrically characterized.