Oxides heterostructures for nanoelectronics

Abstract

We summarise in this paper the work of two groups focusing on the synthesis and characterisation of functional oxide for nanoelectronic applications. In the first section, we discuss the growth by liquid-injection MOCVD of oxides heterostructures. Interface engineering for the minimisation of silicate formation during the growth of polycrystalline SrTiO 3 on Si is first presented. It is realised via the change of reactant flow or chemical nature at the Si surface. We then report on the epitaxy on oxide substrates of manganites films and superlattices and on their magnetic and electrical properties. La 0.7 Sr 0.3 MnO 3 and La 0.8 MnO 3-δ as well as multiferroic hexagonal ReMnO 3 manganites are considered. We show that the film thickness and related strain may be used to tune the properties. Finally, we demonstrate the growth of MgO nanowires by CVD at a moderate temperature of 600°C, using gold as a catalyst. In the second section, we discuss the growth of epitaxial oxide heterostructures by MBE. First, the direct epitaxy of SrTiO 3 on Si is considered. Issues and control of the SrTiO 3 /Si interface are discussed. An abrupt interface is achieved. We show that SrTiO 3 on Si can be used as a buffer layer for the epitaxy of various perovskite oxides such as LaAlO 3 or La 0.7 Sr 0.3 MnO 3 . La 0.7 Sr 0.3 MnO 3 films are ferromagnetic and metallic at room temperature. The epitaxial growth of complex oxides on Si wafers opens up the route to the integration of a wide variety of functionalities in nanoelectronics. Finally, we discuss the monolithic integration of III-V compounds such as InP on Si using epitaxial SrTiO 3 buffer layers for the future integration of optics on Si.

A review of molecular beam epitaxy of ferroelectric BaTiO3films on Si, Ge and GaAs substrates and their applications

“…Apart from this compound, relatively few complex oxides (perovskite, spinel, pyrochlore phases…) have been grown by MBE on Si [55–62]. In many cases, the epitaxial growth on the template layers is completed using other deposition techniques such as pulsed laser deposition, sputtering, chemical vapor deposition or atomic layer deposition, as reported in [64–69] for BaTiO 3 .…”

Engineering of Functional Manganites Grown by MOCVD for Miniaturized Devices

“…Table 1 summarizes the most significant works reported up to now by relevant world‐class groups working in the field. A vast number of manganites systems have been synthetized, including a huge variety of lanthanum manganites (La 1– y A′ y )MnO 3 : La 1– y Sr y MnO 3 (0 ≤ y ≤ 0.65), La 0.7 Ca 0.3 MnO 3 , La 0.8 Ba 0.2 MnO 3 , La 1– y K y MnO 3 (0.05 ≤ y ≤ 0.4), La 0.82 Na 0.18 MnO 3 ; YMnO 3 , and other lanthanide manganites such as Pr 1– y Ca y MnO 3 (0.05 ≤ y ≤ 0.64), Pr 0.6 Sr 0.4 MnO 3 , LuMnO 3 , ErMnO 3 , DyMnO 3 , HoMnO 3 , TbMnO 3 , and NdMnO 3 …”

“…To obtain hetero‐epitaxial manganite films on Si substrates, thin buffer oxide layers with correlated lattice parameters, such as SrTiO 3 , are used . The hetero‐epitaxy is also achieved using single crystal substrates, such as SrTiO 3 (STO, cubic, a = 3.905 Å), LaAlO 3 (LAO, with pseudo cubic lattice constant of 3.788 Å), MgO (cubic, a = 4.205 Å), and NdGaO 3 (NGO, orthorhombic structure with a = 5.426 Å, b = 5.499 Å and c = 7.706 Å) . Therefore, strain engineering can be carried out by combining the film growth on imperfectly lattice‐matched substrates with the growth of additional oxide interlayers .…”

“…For this reason, many relevant studies are focused on studying the strain effect on the LSMO magnetic and electronic properties (commonly measured using a superconducting quantum interference device SQUID magnetometer and using the four‐probe method, respectively). Several groups have reported the epitaxial growth of LSMO thin films onto (001) STO, LAO, and NGO substrates with thicknesses from 1 up to 100 nm (value above which the strain was completely released) …”

“…To further investigate the strain effect, epitaxial LSMO thin films on STO, with thicknesses between ≈1 and 12 nm, were studied . In this case, T C and T M values also diminished with decreasing thickness.…”