Nanoscale Characterization of Silicon-On-Insulator Nanowires by Multimode Scanning Probe Microscopy

Structural and electronic properties of silicon-on-insulator (SOI) nanowires with a cross section area of 20×20 nm2 were investigated with high spatial resolution by multimode scanning probe microscopy (MSPM) in the constant force mode. The position-dependent tunneling current was measured in the interior of the Si nanowires whose surfaces were terminated with hydrogen and with ultrathin thermal oxide. The current value and fluctuations were reduced for Si nanowires terminated with an ultrathin oxide layer (～0.3 nm), indicating the homogeneous surface passivation. The tunneling current decreased within a distance of ~300 nm from the Si pad electrode for both types of surface termination. Calculations of the tunneling current were performed based on the macroscopic conduction model including the conductance contributions of the nanowire volume and the surface states. In the model, the bulk carrier concentration and the surface state density were tuned to fit the experimental data for the small Si nanowires. The results support the length-dependent conductance of thin Si nanowires, demonstrating the ability of the technique for characterization of modern silicon-on-insulator devices.