No abstract

A study of the thermally activated negative fixed charges Qtot and the interface trap densities Dit at the interface between Si and thermal atomic-layer-deposited amorphous Al2O3 layers is presented. The thermal activation of Qtot and Dit was conducted at annealing temperatures between 220 °C and 500 °C for durations between 3 s and 38 h. The temperature-induced differences in Qtot and Dit were measured using the characterization method called corona oxide characterization of semiconductors. Their time dependency were fitted using stretched exponential functions, yielding activation energies of EA = (2.2 ± 0.2) eV and EA = (2.3 ± 0.7) eV for Qtot and Dit, respectively. For annealing temperatures from 350 °C to 500 °C, the changes in Qtot and Dit were similar for both p- and n-type doped Si samples. In contrast, at 220 °C the charging process was enhanced for p-type samples. Based on the observations described in this contribution, a charging model leading to Qtot based on an electron hopping process between the silicon and Al2O3 through defects is proposed.

Charge transport in nanocrystalline SiC with and without embedded Si nanocrystals (Si NCs) prepared by annealing of a−Si1−xCx:H precursors is studied using temperature-dependent current-voltage measurements supported by electron spin resonance and mass spectrometry data. Transport is Ohmic in all films at all temperatures and the temperature dependence of conductivity shows that the materials behave as disordered semiconductors, exhibiting extended-state transport at high temperature and variable-range hopping transport at low temperature. Grain-boundary-, surface-, and interface-dominated transport is systematically ruled out. Films are n type, and films with Si NCs exhibit up to 103 times higher conductivity (up to 0.1Scm−1) after exposure to a hydrogen plasma which passivates dangling bonds, particularly on Si NCs. A forming gas anneal does not have such an effect, indicating that atomic rather than molecular hydrogen is required. The conductivity of SiC films without Si NCs is largely unchanged by passivation and the Fermi level is not raised nearly as closely to the conduction band. This is attributed to a type I band offset between Si NCs and SiC that leads to extended-state conduction in films with Si NCs taking place in a Si network. This is confirmed by the dependence of the extended-state mobility on the volume fraction of excess Si. Variable-range hopping is relatively insensitive to the presence of excess Si and is hence considered to take place via shallow defect states throughout the volume of the films. The high conductivities are found to be a consequence of background doping by oxygen and nitrogen