Structural and optical studies of strain relaxation in Ge1 − xSnx layers grown on Ge/Si(001) by molecular beam epitaxy

•Ge1 − xSnx layers (x = 0.04 and 0.07) grown on (001) Ge buffer layer are partially relaxed.•In the Raman spectra, the Sn–Sn, Sn–Ge and Ge–Ge phonon modes are observed•The HRXRD shows a 0.2° tilt of the (001) lattice planes in the Ge0.93Sn0.07 layer.•The tilt axis is rotated on about 90° with respect to the direction of a substrate miscut.

The structural and optical properties of the Ge1 − xSnx layers with Sn mole fraction x of about 0.04 and 0.07 grown by molecular beam epitaxy on strain relaxed (001) Ge buffer layers have been investigated. The formation of GeSn solid solutions is proved by the high-resolution X-ray diffraction and micro-Raman investigations. The Ge1 − xSnx layers are found to be partially relaxed, the degree of strain relaxation increases from 8% in the layer with x = 0.04 to about 14% in the layer with x = 0.07. For the Ge and Ge1 − xSnx layers the miscut and tilt angles were calculated and compared with those predicted by Nagai's theory. For the Ge1 − xSnx layer with x = 0.07 an abnormally large tilt of about 0.26° of the epilayer (001) lattice planes with respect to the corresponding substrate planes is found. It is shown also that the epilayer tilt axis is rotated on about 90° with respect to the direction of a substrate miscut. The possible mechanisms of the effect are discussed.