Highly boron-doped germanium layers on Si(001) grown by carbon-mediated epitaxy

Smooth and fully relaxed highly boron-doped germanium layers were grown directly on Si(001) substrates using carbon-mediated epitaxy. A doping level of N-A approximate to 1.1 x 10(20 )Cm(-3) was measured by several methods. Using high-resolution x-ray diffraction we observed different lattice parameters for intrinsic and highly boron-doped samples. A lattice parameter of a alpha(Ge:B) 5.653 angstrom was calculated using the results obtained by reciprocal space mapping around the (113) reflection and the model of tetragonal distortion. The observed lattice contraction was adapted and brought in accordance with a theoretical model developed for ultra-highly boron-doped silicon. Raman spectroscopy was performed on the intrinsic and doped samples. A shift in the first order phonon scattering peak was observed and attributed to the high doping level. A doping level of (1.28 +/- 0.19) x 10(20) cm(-3) was calculated by comparison with literature. We also observed a difference between the intrinsic and doped sample in the range of second order phonon scattering. Here, an intense peak is visible at 544.8 cm(-1) for the doped samples. This peak was attributed to the bond between germanium and the boron isotope B-11.