Evolution of optical phonons in epitaxial Ge1-ySnystructures

초록

We report polarized Raman scattering results of Ge1-ySny(0 <= y <= 0.09) epitaxial layers grown on Ge-buffered Si substrates. Polarized Raman spectra from the sample surfaces revealed strong Ge-Ge longitudinal optical (LO) phonon responses. The Ge-Ge LO(z) phonon wavenumber decreased systematically as the Sn content increased. Linear fitting results of the Ge-Ge LO(z) phonon wavenumber shifts as a function of Sn content suggested that a partial strain relaxation occurred in the Ge(1-y)Sn(y)layers. Spatially resolved Raman mapping measurements from the cross section of a Ge(0.938)Sn(0.062)samplev showed that the peak wavenumber of the Ge-Ge transverse optical phonon decreased gradually toward the top surface, providing direct evidence that the residual built-in strain initially formed at the Ge0.938Sn0.062/Ge interface tended to relax gradually along the growth direction. Further, a hydrogen inductively coupled plasma treatment induced a greater homogeneous strain profile in the Ge(0.938)Sn(0.062)layer.

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