Adsorption-Controlled Growth of Ferroelectric PbTiO, and Bi4Ti3O12 Films for Nonvolatile Memory Applications by MBE

Abstract

ABSTRACTEpitaxial PbTiO3 and Bi4Ti3O12 thin films have been grown on (100) SrTiO3 and (100) LaAlO3 substrates by reactive molecular beam epitaxy (MBE). Titanium is supplied to the film in the form of shuttered bursts each containing a one monolayer dose of titanium atoms for the growth of PbTi03 and three monolayers for the growth of Bi4Ti3O12. Lead, bismuth, and ozone are continuously supplied to the surface of the depositing film. Growth of phase pure, c-axis oriented epitaxial films with bulk lattice constants is achieved using an overpressure of these volatile species. With the proper choice of substrate temperature (600 – 650 °C) and ozone background pressure (PO3 = 2×10−5 Torr), the excess of the volatile metals and ozone desorb from the surface of the depositing film leaving a phase-pure stoichiometric crystal. The smooth PbTiO3 surface morphology revealed by atomic force microscopy (AFM) suggests that the PbTiO3 films grow in a layer-by-layer fashion. In contrast the Bi4Ti3O12 films contain islands which evolve either continuously or around screw dislocations via a spiral-type growth mechanism.