Impact of Sn segregation on Ge1−xSnx epi-layers growth by RP-CVD

Abstract

This work investigates the impact of Sn segregation on the growth of Ge1−xSnx epi-layers using a reduced pressure chemical vapour deposition (RP-CVD) system with the common precursors Ge2H6 and SnCl4. The investigated samples were grown on top of a 1 µm thick relaxed Ge buffer layer with different amounts of Sn incorporation, achieved by increasing the SnCl4 partial pressure. The grown Ge1−xSnx epi-layers themselves are fully strained with respect to the Ge buffer underneath. A range of advanced analytical techniques have been used to characterize the material properties. The crystal structure, quality and thickness of the Ge1−xSnx epi-layers were analysed by using cross-sectional high resolution transmission electron microscopy, high resolution X-ray diffraction and fourier transform infrared spectrometry. Atomic force microscopy and Scanning electron microscopy in combination with energy dispersive X-ray spectroscopy are used for analysing the surface. It is shown that simply increasing the SnCl4 partial pressure is insufficient for achieving Sn contents beyond ∼8%. Above these concentrations the epitaxial growth breaks down due to the segregation of Sn resulting in the formation of dots on the epilayer surface, which consist of pure Sn.