ELECTRICAL-PROPERTIES OF PARAELECTRIC (PB0.72LA0.28)TIO3 THIN-FILMS WITH HIGH LINEAR DIELECTRIC PERMITTIVITY - SCHOTTKY AND OHMIC CONTACTS

Linear, paraelectric (Pb0.72La0.28)TiO3 or PLT(28) thin films with a bandgap > 3 eV were deposited on Pt/Ti/SiO2/Si substrates by the sol-gel technique. Specific top-contact metals from two distinct groups (i.e., non-noble or M(T) and noble or M(N); the former being oxidizable transition metals) were selected to understand the electrical nature of the interfaces in terms of electrode dependent energy band diagrams and equivalent circuit models. Using a high sensitivity high-pass filter circuit to evaluate the charging and discharging behavior coupled with results of the thickness and voltage dependence of capacitance, it was determined that M(T) (Ni,Cr,Ti) and M(N) (Pt,Au,Ag) metals form Ohmic and Schottky contacts, respectively. Supported by thermochemical data and calculations, the ohmic M(T)-PLT interfaces are envisioned to be of the form: M(T)-M(T)O(x)-n(+)PLT-nPLT. In contrast, the M(N)-PLT interfaces may be characterized by a metal work function independent Schottky diode; the surface Fermi level being pinned at the mid-gap. For example, a Schottky barrier height of 1.83 eV and a built-in voltage of 1.3 eV at the Pt-PLT interface were estimated. From low field capacitance measurements, the ratio of interfacial to bulk resistance, R(i)/R(b), was estimated to be 23.