Conduction mechanisms and an evidence for phonon-assisted conduction process in thin high-k HfxTiySizO films
Abstract Electrical behavior of high-k Hf x Ti y Si z O layers with different Hf:Ti ratios in the film have been investigated. The films are prepared by MOCVD using novel single-source precursors chemistry. Oxide and interface charges, leakage currents and conduction mechanisms are found to be a strong function of the film composition. The films with lower Hf content show lower level of oxide and interface charges and higher dielectric constant whereas those with higher Hf content have better leakage current properties. It is established that in the films with lower Hf content the conduction is governed by a phonon-assisted process. The change of the conduction mechanism from Poole–Frenkel emission to phonon-assisted tunneling is assigned to possible structural changes which take place when changing the composition of the films.
Application of rapid thermal process to solution-processed Ti-silicate films for enhancing permittivity without losing amorphous nature
Abstract Nanoscale thick Ti-silicate films were synthesized by the solution process on Si(100) substrates, followed by post annealing of rapid thermal process (RTP). The film retained its amorphous structure with a remarkably enhanced permittivity ( k ) value: the k values of the Ti-silicate layer and overall film were increased from 8.6 to 16.2 and from 4.9 to 9.7, respectively, by performing RTP at 700 °C for 1 min. The k value of the interfacial layer between the Ti-silicate and Si was almost unchanged (∼7) after RTP. The FT-IR and XPS analyses indicated that the films had Ti–O–Si bonding relating to the segregated phases of Ti- and Si-rich silicates before RTP. The segregated nature of the sample before RTP was probably due to the different hydrolysis rates of the Si and Ti precursors and/or nanoscale thickness. The degree of segregation further increased after RTP, resulting in a significant improvement of the k value of the Ti-silicate.
Hopping conductivity in disordered solids
A review is given on the hopping conductivity in disordered solids. Variable range hopping between localized electronic states near the Fermi level in amorphous tetrahedrally coordinated semiconductors is discussed in particular. The percolation theory for this type of transport is presented and used to discuss the various transport experiments. These include the dependence of the dc conductivity on heat treatment, applied field, thickness of the samples, and on ion bombardment. It is shown that these effects can be explained satisfactorily by ad hoc models for the density of localized states, although a real understanding of the nature and distribution of these states is still lacking.