In the range 80 K-900 K, we have investigated the electrical properties of heavily aluminum in-situ doped, 4H-SiC samples. The temperature dependence of the hole concentration and Hall mobility was analyzed in the model taking into account heavy and light holes. The modelisation parameters were compared with experimental values of Secondary Ion Mass Spectroscopy (SIMS) and Capacitance-Voltage (CV) measurements.
ABSTRACTWe have performed electrical transport measurements on ultrathin films of epitaxial CoSi2 on Si(111) with film thickness ranging down to ∼10A. The resistivities exhibit temperature dependences characteristic of a metal and a thickness dependence which rises steeply with decreasing thickness suggestive of a quantum size effect. At the lowest temperatures (≲ 10K) the resistivities of the thinner films increase logarithmically with inverse temperature characteristic of transport in the weak localization regime as has been confirmed by magnetoresistance measurements. Hall effect measurements establish that carrier densities (holes) in the ultrathin films are essentially identical to those in bulk CoSi2, i.e. 26 × 1022 cm−3.
The charge transport mechanisms in nanostructured porous silicon (PS) films were studied through current-voltage (I-V) measurements of planar Au/PS/Au structures at 300 K. The films were formed by electrochemical etching of 1-5 Ω-cm p-type Si (100) wafers producing PS layers of 4.48 x 109 Ω-cm. The charge transport is limited both by the space charge limited currents (SCLC) and the carrier trapping-detrapping kinetics in the inherent localized PS energy levels. I-V characteristics evolve according to the trapping-detrapping carrier kinetics in the PS films showing that the electrical current can be controlled by applying external electric fields. An equivalent trap filling limiting voltage (VTFL) was identified that shifts between 1 and 3 volts by the carrier trapping-detrapping kinetics from the PS intrinsic defect states. An energy band diagram for the PS films is schematically depicted including the influence of the intrinsic PS defect states. To give a reasonable explanation of the found behavior the existence of a thin silicon oxide film covering the network-like-silicon-nanocrystallites is required, in agreement with the widely accepted PS structural models.
AbstractIn this paper we have formulated the electronic contribution to the elastic constants in ultrathin films of p-Si by considering the influences of heavy, light and split-off holes respectively. We have suggested an experimental method of determining the same in degenerate materials having arbitrary dispersion laws. The elastic constants increase with increasing hole concentration in an oscillatory way and decrease with increasing film thickness. The theoretical formulation is in agreement with the suggested experimental method of determining second and third order elastic constants.
AbstractA cobalt ultrathin film, which shows a large change in Curie temperature by an electric field application, has been studied by x-ray reflectometry with applying electric fields. The cobalt film was made by the sputtering method on top of a Pt buffer layer, and capped with a MgO layer. X-ray reflectometry shows that the change in Co thickness caused by the applied voltage up to ±10 V was less than 0.06 Å. The reflectivity signal intensity shows a characteristic kink at the Co
A Chemical Vapor Deposition graphene monolayer grown on 6H–SiC (0001) substrates was used for implantation experiments. The graphene samples were irradiated by He+ and N+ ions. The Raman spectra and electrical transport parameters were measured as a function of increasing implantation fluence. The defect concentration was determined from intensity ratio of the Raman D and G peaks, while the carrier’s concentration was determined from the relations between G and 2D Raman modes energies. It was found that the number of defects generated by one ion is 0.0025 and 0.045 and the mean defect radius about 1.5 and 1.34 nm for He+ and N+, respectively. Hole concentration and mobility were determined from van der Pauw measurements. It was found that mobility decreases nearly by three orders of magnitude with increase of defect concentration. The inverse of mobility versus defect concentration is a linear function, which indicates that the main scattering mechanism is related to defects generated by ion implantation. The slope of inverse mobility versus defect concentration provides the value of defect radius responsible for scattering carriers at about 0.75 nm. This estimated defect radius indicates that the scattering centres most likely consist of reconstructed divacancies or larger vacancy complexes.
Electrical transport during growth, aging and oxidation of copper ultrathin films before percolation
