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 b andgap > 3 eV were deposited on Pt/Ti/SiO2/Si substrates by the sol-ge l 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 tr ansition metals) were selected to understand the electrical nature of the interfaces in terms of electrode dependent energy band diagrams an d equivalent circuit models. Using a high sensitivity high-pass filter circuit to evaluate the charging and discharging behavior coupled wit h results of the thickness and voltage dependence of capacitance, it w as determined that M(T) (Ni,Cr,Ti) and M(N) (Pt,Au,Ag) metals form Ohm ic and Schottky contacts, respectively. Supported by thermochemical da ta and calculations, the ohmic M(T)-PLT interfaces are envisioned to b e of the form: M(T)-M(T)O(x)-n(+)PLT-nPLT. In contrast, the M(N)-PLT i nterfaces may be characterized by a metal work function independent Sc hottky 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 capac itance measurements, the ratio of interfacial to bulk resistance, R(i) /R(b), was estimated to be 23.