Pulsed laser deposition of Zr_1-xCe_xO₂ and Ce_1-xLa_xO_2-x/2 for buffer layers and insulating barrier in oxide heterostructures

We have studied the pulsed laser deposition (PLD) of Zr_1-xCe_xO₂ and Ce_1-xLa_xO_2-x/2 initially to grow buffer layers for perovskite films deposited on Si, LaAlO₃ and MgO and then to produce tunneling barriers for cuprate or manganite heterostructures. On (100) Si, the deposition of Zr_1-xCe_xO₂ (x = 0.12) produces a smooth epitaxial layer (R_RMS = 0.25 nm/1 μm²), which allows the further deposition of high quality YBa₂Cu₃O₇ (Tc ≥ 88 K) and La_0.7Sr_0.3MnO₃ films. On the other hand, the use of Ce_1-xLa_xO_2-x/2 (0 ≤ x ≤ 0.4) makes it possible to match the YBa₂Cu₃O₇ and La_0.7Sr_0.3MnO₃ layers to various substrates. The buffer layers are epitaxially grown with a 45° rotation of the in-plane axes with respect to those of the substrate, and the smoothness is high (R_RMS = 0.24 nm/1 μm²). In the case of an ultra-thin barrier (≅ 2.5 nm) of Ce_1-xLa_xO_2-x/2 sandwiched in a La_0.7Sr_0.3MnO₃, the out-of-plane mismatch of √2 induces distortions at the interface steps, which propagate into the topmost La_0.7Sr_0.3MnO₃ layer. This is in contrast to the case of SrTiO₃ barriers where an ideal crystal continuity in the growth direction is observed.