Dependence of Semiconductor to Metal Transition of VO2(011)/NiO{100}/MgO{100}/TiN{100}/Si{100} Heterostructures on Thin Film Epitaxy and Nature of Strain

Abstract

We have studied semiconductor to metal transition (SMT) characteristics of VO2(011) thin films integrated epitaxially with Si(100) through NiO{001}/MgO{001}/TiN{001} buffer layers and correlated with the details of epitaxy and nature of residual stresses and strains across the VO2/NiO interface. Thin film epitaxy at both room and elevated temperatures is studied in detail by electron microscopy and in situ high‐temperature X‐ray diffraction techniques. The epitaxial relationship across the interface between monoclinic VO2 and NiO is determined to be (011)VO2||{100}NiO and [01]VO2||[001]NiO at room temperature. The epitaxial alignment at the temperature of growth where tetragonal VO2 is stable is determined as: (110)VO2||{100}NiO and [001]VO2||[100]NiO. A cube‐on‐cube crystallographic alignment is established across the NiO{100}/MgO{100}/TiN{100}/Si{100} interfaces. The misfit strains across the VO2/NiO interface at the growth temperature are calculated and the mechanism of strain relaxation is discussed. The out‐of‐plane orientation is found to be relaxed in both monoclinic and tetragonal states of VO2. It is shown that a compressive strain of 31.65% along the [001] direction of tetragonal VO2 is fully relaxed via matching of multiple domains. However, a small tensile misfit strain of about 5% along [10] direction cannot relax and remains in the lattice. This tensile residual strain leads to a compressive strain along [001] axis which, in turn, results in an SMT temperature slightly lower than that of freestanding strain‐free VO2. SMT characteristics of VO2(011) epilayers are assessed where an amplitude of near five orders of magnitude, and a hysteresis of less than 3.6 °C are obtained. This study introduces VO2/NiO thin film heterostructure integrated with silicon as a promising candidate for multifunctional devices with novel characteristics where a combination of sensing, manipulation, and response functions is needed.