Critical thickness of high structural quality SrTiO3 films grown on orthorhombic (101) DyScO3

Abstract

Strained epitaxial SrTi0 3 films were grown on orthorhombic (I 0 I) DySC03 substrates by reactive molecular-beam epitaxy. The epitaxy of this substrate/film combination is cube on cube with a pseudocubic out-of-plane (001) orientation. The strain state and structural perfection of films with thicknesses ranging from 50 to 1000 A were examined using x-ray scattering. The critical thickness at which misfit dislocations was introduced was between 350 and 500 A. These films have the narrowest rocking curves (full width at half maximum) ever reported for any heteroepitaxial oxide film (0.001 8°). Only a modest amount of relaxation is seen in films exceeding the critical thicknesses even after postdeposition annealing at 700 °C in I atm of oxygen . The dependence of strain relaxation on crystallographic direction is attributed to the anisotropy of the substrate. These SrTi0 3 films show structural quality more typical of semiconductors such as GaAs and silicon than perovskite materials; their structural relaxation behavior also shows similarity to that of compound semiconductor films.

Properties of rare-earth scandate single crystals (Re=Nd−Dy)

“…The average FWHM is 23 arcsec for the DyScO 3 wafer and 20 arcsec for the GdScO 3 wafer. These values are bit higher than those published a year ago [20] and we do note differences from boule to boule, with some DyScO 3 and GdScO 3 substrates having FWHM as narrow as 7 arcsec [11,17,18]. However, these values are significantly narrower than the rocking curve FWHM of SrTiO 3 bulk crystals [32][33][34].…”

“…Table 2 Refined lattice constants of the grown RE scandates Table 3 Lattice mismatch at room temperature between the nearly square mesh spanned by a p1 ¼ a p2 ¼ 0.5 ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi a 2 þ b 2 p and a p3 ¼ 0.5c of the (1 1 0) surface of the grown RE scandates and (1 0 0) SrTiO 3 (a 0 ¼ 3.905 Å ) and (0 0 1) BaTiO 3 (a 0 ¼ 3.99 Å ) Table 4 Average thermal expansion coefficients of DyScO 3 , TbScO 3 , GdScO 3 , SmScO 3 , and TbScO 3 over the temperature range indicated a 11 (10 À6 K À1 ) a 22 (10 À6 K À1 ) a 33 (10 À6 K À1 ) a av  (10 À6 K À1 ) Thus from the standpoint of crystalline perfection, these RE scandate crystals are vastly superior to SrTiO 3 for use as substrates and not surprisingly have enabled the growth of heteroepitaxial oxide films with the narrowest FWHM ever achieved [11,17,18].…”

“…SrTiO 3 films deposited on DyScO 3 and BaTiO 3 films deposited on DyScO 3 and GdScO 3 showed biaxial in-plane strains of 1.0%, À1.0%, and À1.6% [9,10]. The critical thickness for the onset of relaxation of the SrTiO 3 /DyScO 3 films, the system that has been studied in the most detail to date, is around 400 Å [18].…”

“…The biaxial strain e s is defined by s ¼ ða k À a 0 Þ=a 0 where a J is the in-plane lattice parameter of the biaxially strained film which directly depends on the lattice mismatch, and a 0 is the lattice parameter of the unstrained film. If the lattice mismatch between film and substrate is too large, however, dislocations will arise in the very early stages of growth leading to broadened rocking curves of the films due to the increased mosaic spread of the film orientation [18]. Because the critical film thickness for dislocation formation depends nearly inversely on the lattice mismatch, a lower mismatch within narrow limits is needed to grow strained, low-dislocation density films of usable thicknesses.…”

Fabrication and convergent X-ray nanobeam diffraction characterization of submicron-thickness SrTiO3 crystalline sheets

“…X-ray nanodiffraction using tightly focused beams indicates that the increase in the rocking curve width is at most a factor of two, small enough that mosaic widths fall within a range typically used for epitaxial growth. 28 The development of the x-ray nanobeam analysis methods employed in this work was supported by the U. …”