Characterization of impurity doping and stress in Si/Ge and Ge/Si core-shell nanowires.

Core-shell nanowires (NWs) composed of silicon (Si) and germanium (Ge) are key structures for realizing high mobility transistor channels, since the site-selective doping and band-offset in core-shell NWs separate the carrier transport region from the impurity doped region, resulting in the suppression of impurity scattering. Four different types of Si/Ge (i-Si/n-Ge, p-Si/i-Ge) and Ge/Si (n-Ge/i-Si, i-Ge/p-Si) core-shell NWs structures were rationally grown. The surface morphology significantly depended on the types of the core-shell NWs. Raman and X-ray diffraction (XRD) measurements clearly characterized the compressive and tensile stress in the core and shell regions. The observation of boron (B) and phosphorus (P) local vibrational peaks and the Fano effect clearly demonstrated that the B and P atoms are selectively doped into the shell and core regions and electrically activated in the substitutional sites, showing the success of site-selective doping.