Core-shell nanowires (NWs) composed of silicon and germanium can be used to realize high electron (hole) mobility transistors (HEMTs) by suppressing impurity scattering due to their band offset structure and selective doping. Boron doped p-type Si/intrinsic-Ge (i-Ge) core-shell NW structures are selected to study this phenomenon. To produce HEMT devices, hole gas accumulation must be controlled in the impurity undoped i-Ge shell layers. Spectral change in the Ge optical phonon is detected with increased B doping in p-Si core NWs, showing hole gas accumulation in this system. We also fabricate p-Si/i-Ge/p-Si core-double shell NWs to more clearly demonstrate hole gas accumulation in the i-Ge layers.