No abstract

No abstract

Time-zero current-voltage characteristics and time-dependent current behavior of metal-ferroelectric-metal (Pt-PZT-Pt) capacitor structures have been studied. Under constant-voltage stressing, the current density through the 1500-Å-thick lead-zirconate-titanate (PZT) film exhibits a power-law dependence on time, with the exponent (∼0.33) independent of temperature and voltage. Electrode material dependence of current density indicates that the conventional model of trap-limited single-carrier injection over nonblocking contacts is inadequate to explain the time-zero current. A change in top electrode material from Pt to In leads to the observation of work-function-driven Schottky contacts between the metal and ferroelectric. The current-voltage characteristics fit a two-carrier injection metal-semiconductor-metal model incorporating blocking contacts, with distinct low- and high-current regimes (PZT is assumed to be p-type and trap-free in this model). Temperature-dependent I-V measurements indicate a Pt-PZT barrier height of 0.6 eV and an acceptor doping level of ∼1018 cm−3 in PZT. The implications of this model on the optimization of ferroelectric capacitors for dynamic random access memory applications are discussed.

Hetero-epitaxy of single-crystal perovskite SrTiO3 on GaAs(001) was achieved using molecular beam epitaxy. The growth was accomplished by deposition of a submonolayer of titanium on GaAs(001), followed by the co-deposition of strontium and titanium initiated at a low-temperature, low-oxygen-pressure condition. X-ray photoelectron spectroscopy showed that the Ti prelayer reacted with As and formed TiAs-like species on the As terminated GaAs(001) surface. Reflection-high-energy-electron diffraction showed that SrTiO3 grew coherently on the GaAs(001) at early stage of growth. This coherent behavior began to degrade when SrTiO3 thickness exceeded 20Å. Cross-sectional transmission electron microscopy revealed an abrupt interface between SrTiO3 and GaAs and good crystallinity of the SrTiO3 film. An epitaxial relationship between SrTiO3 and GaAs was further confirmed by x-ray diffraction. The success of growth of SrTiO3 on GaAs paves the way for integration of various functional perovskite oxides with GaAs.