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

This work investigates the impact of Sn segregation on the growth of Ge
_1-x
Sn
_x
epi-layers using a reduced pressure chemical vapour deposition (RP-CVD) system with the common precursors Ge
₂
H
₆
and SnCl
₄
. 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 SnCl
₄
partial pressure. The grown Ge
_1-x
Sn
_x
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 Ge
_1-x
Sn
_x
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 SnCl
₄
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.