Clear Experimental Demonstration of Hole Gas Accumulation in Ge/Si Core-Shell Nanowires.

Selective doping and band-offset in germanium (Ge)/silicon (Si) core-shell nanowire (NW) structures can realize a type of high electron mobility transistor structure in one-dimensional NWs by separating the carrier transport region from the impurity-doped region. Precise analysis, using Raman spectroscopy of the Ge optical phonon peak, can distinguish three effects: the phonon confinement effect, the stress effect due to the heterostructures, and the Fano effect. The Fano effect is the most important to demonstrate hole gas accumulation in Ge/Si core-shell NWs. Using these techniques, we obtained conclusive evidence of the hole gas accumulation in Ge/Si core-shell NWs. The control of hole gas concentration can be realized by changing the B-doping concentration in the Si shell.