S. Privitera

Amorphous-to-crystal transition of nitrogen- and oxygen-doped Ge2Sb2Te5 films studied by in situ resistance measurements

The amorphous-to-crystal transition has been studied through in situ resistance measurements in Ge2Sb2Te5 thin films doped by ion implantation with nitrogen or oxygen. The dependence of the electrical resistivity and structure on the annealing temperature and time has been investigated in samples with different dopant concentrations. Enhancement of the thermal stability and increase of the mobility gap for conduction have been observed in O- and N-doped amorphous Ge2Sb2Te5. Larger effects have been found in the case of nitrogen doping.

Crystal nucleation and growth processes in Ge2Sb2Te5

The kinetics of the amorphous-to-crystal transition in Ge2Sb2Te5 thin films have been studied through in situ transmission electron microscopy analyses. By following the time evolution of the grain density and size, the growth velocity and the nucleation rate have been separately measured at different annealing temperatures. Activation energies of 2.9±0.5 eV and 2.3±0.4 eV have been obtained for the nucleation rate and the growth velocity, respectively. The barrier energy for the nucleation of a critical nucleus ΔG* has been evaluated, and the scalability of phase change nonvolatile memories has been estimated.

Crystallization and phase separation in Ge2+xSb2Te5 thin films

The electrical properties and the structure of isothermally annealed thin films of Ge2+xSb2Te5 (x=0 and 0.5) have been studied by in situ electrical measurements, x-ray diffraction, and transmission electron microscopy analyses. Phase separation has been observed in samples with an excess of Ge; by annealing amorphous Ge2.5Sb2Te5 films at temperatures in the range 130–160 °C, the material cannot be completely converted into the metastable face-centered-cubic (fcc) structure. At temperatures higher than 160 °C, the residual amorphous material may be converted into a fcc structure with a lower lattice parameter.

Direct measurement of the growth rate during the C49 to C54 transformation in TiSi2: Activation energy

The growth rate of the C54 phase of TiSi 2 inside a C49 matrix has been measured by micro-Raman imaging by following the time evolution of the C54 grain radius. The measurement is the most direct that has been achieved up to now, being completely independent of the nucleation process. From the Arrhenius plot, an activation energy of 3.8±0.6 eV the growth process alone has been determined.

Nucleation and growth of C54 grains into C49 TiSi2 thin films monitored by micro-Raman imaging

The first-order C49–C54 allotropic-phase transition has been studied in TiSi2 thin films by electrical measurements and micro-Raman spectroscopy. To evaluate the parameters describing the kinetics of the transition and the barrier energy for the nucleation, micro-Raman spectroscopy has been used as a microscopy technique: spectra have been acquired scanning large silicide areas (100×50 μm2) and have been processed to obtain images which show the morphological evolution of the C54 grains during the transition. For temperatures between 680 and 720 °C, the converted area fraction has been determined at different annealing times and compared with electrical measurements. The two methods agree quite well. Both density and size of the C54 grains have been measured, thus allowing to separately determine the nucleation and growth parameters as a function of temperature. A nucleation and growth model has been fitted to data obtaining an activation energy of 4.9±0.7 eV for the nucleation rate and 4.5±0.9 eV for the...

Electrical and structural characterization of metal–oxide–semiconductor capacitors with silicon rich oxide

Metal–oxide–semiconductor capacitors in which the gate oxide has been replaced with a silicon rich oxide (SRO) film sandwiched between two thin SiO2 layers are presented and investigated by transmission electron microscopy and electrical measurements. The grain size distribution and the amount of crystallized silicon remaining in SRO after annealing have been studied by transmission electron microscopy, whereas the charge trapping and the charge transport through the dots in the SRO layer have been extensively investigated by electrical measurements. Furthermore, a model, which explains the electrical behavior of such SRO capacitors, is presented and discussed.

Correlation of dot size distribution with luminescence and electrical transport of Si quantum dots embedded in SiO2

Abstract We have investigated the electrical transport and luminescence of Si dots embedded in SiO 2 . The dots have been obtained by high temperature annealing of silicon rich oxides prepared by chemical vapor deposition. Transmission electron microscopy analysis demonstrates the presence of crystalline Si dots with grain radii down to 1 nm. The data of luminescence and electrical transport appear correlated with the dot size distribution. Moreover, the analysis of the electrical characteristics of metal-oxide–semiconductor capacitors with silicon rich oxide films indicates that such systems may reversibly store charge, thus exhibiting the function of a memory.

Simulation of the transformation from the C49 to the C54 phase of TiSi2 in blanket films and narrow conductors

The C49–C54 phase transition has been simulated by Monte–Carlo calculations in blanket films and conductors using a unitary model based on transient nucleation and growth which takes into account the temperature dependence of the nucleation parameters. The output of the model has been compared with experimental data from electrical measurements in blanket films and 0.5 μm wide conductors. The comparison allows us to determine the density of available nucleation sites and to interpret the spread of experimental data, observed in the case of lines, as fluctuations in the number of sites and in their random location.

Kinetics of the C49-C54 transformation in patterned and blanket TiSi 2 films: a comparison

The kinetics of the C49-C54 polymorphic transformation in titanium disilicides thin films grown on amorphous Si substrate has been followed by sheet resistance and Infrared Spectroscopy measurements on both blanket samples and submicron lines. The transformation of a fine grained C49 films (d avg =30 nm) into the C54 phase was complete after annealing for ∼300 s at a temperature of 700 °C in blanket samples and of 730 °C in submicron lines. The Avrami exponent decreases from n=3 in blanket films to n=l in stripes. The transformation time at a given temperature increases with decreasing linewidth in agreement with the nucleation density model. Infrared Spectroscopy shows no shift of the peaks of the C49 phonons going from blanket to patterned films, suggesting the lack of strain on TiSi 2 patterned films. The different behavior between blanket and laterally limited samples has been explained in terms of the different surface energies.