Properties of Si Nanowhiskers Coated by TiOx and TiONx Layers

Chemical and electrical passivation of Si nanowhiskers (NW) by means of plasma chemical oxidation and nitridation of Ti nanolayers evaporated onto MBE-grown Si NW were used. Influence of formed Ti nanolayers on the properties of Si NWs were evaluated by means of scanning electron microscopy, and current-voltage and current-temperature measurements. Specific aspects addressed in the present study were modification of the morphology and electrical properties of Si NWs after plasma chemical treatments of samples resulting in the formation of TiOx or TiONx layers on the NWs surface. It is shown that at temperatures close to room temperature the conductivity of NWs, as well as that of the silicon substrate on which the NWs were grown, was defined by centers with ionization energies (0.20-0.22) eV. Depending on particular conditions, the plasma treatments used to form the TiOx or TiONx layers on the NW surface brought about the following phenomena: (i) introduction of centers with ionization energies 0.12 eV and (0.03-0.04) eV that defined the conduction of Si NWs at temperatures below 160 K and (ii) change of shape of the NWs (from cylindrical to conical) that may prove useful for optical applications of Si NWs. On the basis of NW arrays, surround-gate field-effect transistors (FETs) with SiO2/TiONx composite dielectric were fabricated. The threshold-voltage value of the FETs, Vth=0.3 V, and the dielectric constant of the TiONx layers ε=14.7 at frequency 100 kHz were evaluated.