M. de Keijser

Epitaxial PbTiO3 thin films grown by organometallic chemical vapor deposition

Epitaxial PbTiO3 layers have been grown on (001)SrTiO3 substrates by organometallic chemical vapor deposition using the precursors titanium‐iso‐propoxide and tetra‐ethyl‐lead. The growth temperature for these films was around 700 °C. The epitaxial nature of c‐axis‐oriented PbTiO3 is confirmed by Rutherford backscattering spectrometry, x‐ray diffraction, including pole figure analysis, and high‐resolution electron microscopy (HREM). With HREM twinning has been observed.

Effects of crystallite size in PbTiO3 thin films

The lattice constants of tetragonal PbTiO3 grown by organometallic chemical vapor deposition, vary with average crystallite size in the thin film as determined from line broadening in x‐ray diffraction patterns. The a‐ and c‐lattice constants become equal when the average crystallite size decreases to below ∼5 nm. These data agree with the change in lattice constants as a function of average crystallite size found recently for submicron PbTiO3 powder.

Structural and electrical characterization of heteroepitaxial lead zirconate titanate thin films

PbZrxTi1−xO3 films have been grown heteroepitaxially onto (001)SrTiO3 and SrRuO3/(001)SrTiO3 by organometallic chemical vapor deposition. As a start, the microstructure of PbZrxTi1−xO3 films on (001)SrTiO3 was studied as a function of the zirconium fraction, x. Rutherford backscattering spectrometry, including channeling experiments, and transmission electron microscopy have shown that the microstructure is dominated by the crystal structure of the PbZrxTi1−xO3. In the case of tetragonal PbZrxTi1−xO3 the films may contain a‐axis oriented regions. These regions have not been observed for films with a composition giving a rhombohedral unit cell. Despite the rather large mismatch of rhombohedral PbZrxTi1−xO3 with the (001)SrTiO3, values as low as 4% for the minimum channeling yield have been obtained. For a rhombohedral film the ferroelectric properties have been measured. To this end a single crystalline PbZr0.8Ti0.2O3 film was grown onto (001)SrTiO3 provided with a heteroepitaxial SrRuO3 electrode grown by...

Composition-controlled growth of PbTiO3 on SrTiO3 by organometallic chemical vapour deposition

Abstract PbTiO 3 thin films have been grown on (001)SrTiO 3 by organometallic chemical vapour deposition (OMCVD) using the precursors tetra-ethyl-lead (TEL) and tetra-isopropoxy-titanium (TIP). The kinetics of the growth process have been studied as a function of the substrate temperature and the partial pressures of TEL, TIP and oxygen. At temperatures of 700°C and higher, the composition of the layers corresponds to stoichiometric PbTiO 3 , independent of the deposition temperature, oxygen partial pressure and the ratio of TEL and TIP partial pressures, which was varied between 0.2 and 1.7. This independency of growth condition can be explained by a mechanism involving the competition between the desorption of PbO and a fast formation of PbTiO 3 by the reaction of PbO with TiO 2 . At 700°C the growth rate of PbTiO 3 is proportional to the TIP partial pressure, but decreases with increasing TEL partial pressure, indicative of a competitive adsorption of Pb- and Ti-containing species. The growth rate is limited by the supply of TIP. Under optimal growth conditions, layers are obtained having a Rutherford backscattering channeling minimum yield as low as 3%.

Atomic layer epitaxy of gallium arsenide with the use of atomic hydrogen

Monolayer atomic layer epitaxy of GaAs has been achieved between 430 and 500 °C by using alternating pulses of AsH3, Ga(CH3)3, and atomic hydrogen. Maintaining the susceptor temperature below 500 °C suppresses the unfavorable thermal decomposition of Ga(CH3)3 to Ga in the gas phase. The basic point of our growth method is that, notwithstanding these low temperatures, sufficiently fast surface kinetics for growth are maintained by activation with the atomic hydrogen pulses.

High quality lead zirconate titanate films grown by organometallic chemical vapour deposition

Abstract Organometallic chemical vapour deposition is a suitable technique for the deposition of thin films of oxidic compounds such as lead zirconate titanate, PbZrxTi1−xO3. Above a deposition temperature of about 600°C stoichiometric PbZrxTi1−xO3 films can be grown on platinized silicon wafers within a large process window, independent of the precursor partial pressures and the deposition temperature. This is the result of a self-regulating mechanism. The PbZrxTi1−xO3 films have excellent ferroelectric properties exhibiting high values, up to 60μC/cm2, for the remanent polarisation. The value of the coercive field strength varies between 50 and 180 kV/cm, dependent on the composition. Layers with comparable properties can also be grown at lower temperatures, down to 500°C. In this case careful control of the gas-phase composition is required to obtain films with the correct stoichiometry.

Peculiar asymmetric flow pattern in a vertical axisymmetric VPE reactor

Both visualization experiments and simulations show that in axisymmetric VPE reactors with top inlet, for symmetrical boundary conditions at atmospheric pressure generally an asymmetric rather than a symmetric vortex is stable.

Ferroelectric PbZr x Ti 1-x O 3 Thin Films Grown by Organometallic Chemical Vapor Deposition

For the successful integration of ferroelectric thin films in IC technology, there is a need for a deposition technique capable of growing homogeneous layers at high growth rates over large-area structured substrates. Organometallic chemical vapor deposition (OMCVD) is a promising technique for meeting these demands. Ferroelectric layers of PbZr x Ti 1-x O 3 (PZT) were grown by OMCVD on Pt-coated 10 cm diameter Si-substrates using the precursors tetra-ethyl-lead, tetra-iso-propoxy-titanium and tetra-tertiary-butoxy-zirconium at 700 °C without any post anneal. At this temperature the layers are single phase and highly (h00) and/or (00l) oriented. The layers show good ferroelectric switching properties with high remanent polarizations, but also with high coercive field strengths. Fatigue measurements are presented for these OMCVD grown PZT layers. The layers have a switching lifetime exceeding 10 11 cycles at a switching amplitude of 5 V.

The structure of heteroepitaxial lead titanate layers grown by organometallic chemical vapour deposition

The structure of heteroepitaxial (001) lead titanate films on (001) strontium titanate and (001) magnesium oxide grown by organometallic chemical vapour deposition has been investigated. PbTiO3 grows textured on (001)MgO and heteroepitaxially on (001)SrTiO3. Details of the microstructure are, however, comparable. Rutherford backscattering spectrometry (RBS) channelling experiments on heteroepitaxial PbTiO3 films on (001)SrTiO3 have shown that the microstructure is dominated by the layer thickness. The cooling rate is found to have no influence on the microstructure. Very thin films to about 50 nm thickness show a relatively large value of the minimum channelling yield which decreases with increasing thickness. For film thicknesses between about 50 nm and 100 nm the minimum channelling yield is relatively low, down to a few percent, indicative of high-quality epitaxial films. If the film thickness exceeds a critical value of about 100 nm the epitaxial quality deteriorates as can be concluded from the sharp increase in the value for the minimum yield. Changes in minimum yield are due to changes in the microstructure of the film which has been studied by transmission electron microscopy (TEM) and X-ray diffraction. TEM and {100}PbTiO3 pole-figure measurements show the presence of a-axis oriented domains sharing {101} twin planes with the c-axis matrix. The volume fraction has been estimated from θ–2θ scans as a function of offset in θ. For thick films the volume fraction scales with the minimum yield. This analysis is confirmed by rocking-width measurements. The presence of non-uniform residual strain in the film has been analyzed from broadening of the (001)PbTiO3 diffraction lines. Details of the microstructure are correlated with the RBS data. A tentative interpretation is presented.

Modelling of organometallic chemical vapour deposition of lead titanate

Abstract The growth of lead titanate by organometallic chemical vapour deposition using the precursors tetraethyllead, tetraisopropoxidetitanium and oxygen, is modelled. An initial partial decomposition of the precursors is postulated to take place in the gas phase. These partial decomposed species then diffuse to the surface followed by a dissociative adsorption. The Pb and Ti adsorbates make use of the same sort of adsorption site thereby introducing a competitive adsorption mechanism. In a next step the adsorbates decompose further and react with adsorbed oxygen, leading to the formation of intermediate compounds of lead oxide, and titanium dioxide. These individual oxides then either react to form the lead titanate or are incorporated in the film as such. Desorption of the intermediate lead oxide compound is included in the model. The model may be used to describe the dependence of the growth rate and the composition of the layer as a function of the deposition temperature, precursor and oxygen partial pressures. A reasonable agreement between the model predictions and experimental results is obtained.