Electrical Properties of Paraelectric (Pb_0.72La_0.28)TiO₃ Thin Films with High Linear Dielectric Permittivity: Schottky and Ohmic Contacts

Abstract

Linear, paraelectric (Pb 0.72 La 0.28 )TiO 3 or PLT(28) thin films with a bandgap>3 eV were deposited on Pt/Ti/SiO 2 /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- n PLT. 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.