Interface charge induced p-type characteristics of aligned Si _1-xGe_x Nanowires

This study reports the electrical transport characteristics of Si ₁-_xGe_x (x = 0-0.3) nanowires. Nanowires with diameters of 50-100 nm were grown on Si substrates. The valence band spectra from the nanowires indicate that energy band gap modulation is readily achievable using the Ge content. The structural characterization showed that the native oxide of the Si₁-_xGe_x nanowires was dominated by SiO₂; however, the interfaces between the nanowire and the SiO₂ layer consisted of a mixture of Si and Ge oxides. The electrical characterization of a nanowire field effect transistor showed p-type behavior in all Si₁-_xGe_x compositions due to the Ge-O and Si-O-Ge bonds at the interface and, accordingly, the accumulation of holes in the level filled with electrons. The interfacial bonds also dominate the mobility and on- and off-current ratio. The large interfacial area of the nanowire, together with the trapped negative interface charge, creates an appearance of p-type characteristics in the Si₁-_xGe _x alloy system. Surface or interface structural control, as well as compositional modulation, would be critical in realizing high-performance Si₁-_xGe_x nanowire devices.