Hall Effect Measurements in Rotating Magnetic Field on Sub-30-nm Silicon Nanowires Fabricated by a Top–Down Approach

We present the nanofabrication and transport properties of single silicon nanowires (NWs) having mean widths in the range from sub-30 to 500 nm. Hall effect measurements are undertaken in the magnetic fields of 14 T at 300 K. The NWs are defined by electron-beam lithography (EBL) using the negative tone resist hydrogen silsesquioxane (HSQ) as a mask for reactive ion etching (RIE). Silicon NWs are patterned on nonuniform highly doped n-type silicon-on-insulator (SOI) substrates. The doping profile has been observed to show a significant effect on the NW electrostatics, which in turn influences the contact and transport properties of the NWs. For the formation of Hall electrodes, we have employed an angled substrate evaporation technique, where the NW itself is used as a shadow mask and an intimate sidewall contact has been formed. The Hall electrodes are not opposite to each other in this case; therefore, the longitudinal resistance pickup had to be considered when extracting the Hall signal of the NW. The mobility of these NWs is discussed. For the narrowest 40-nm-wide silicon NW, the obtained value of mobility is 292 ± 6 cm
²
/Vs and, for the blanket, nonpatterned device layer, it is 100 ± 0.1 cm
²
/Vs. The effective mobility increases as the width of the NWs decreases. This is attributed to the reduced dimensionality of the electron transport in the NWs. Both the electrical and effective thicknesses of the NW change at small physical width, which results in enhanced electron transport within the channel and enhances the value of the measured Hall signal.