Abstract
Transition metal oxides offer functional properties beyond conventional semiconductors. Bridging the gap between the fundamental research frontier in oxide electronics and their realization in commercial devices demands a wafer-scale growth approach for high-quality transition metal oxide thin films. Such a method requires excellent control over the transition metal valence state to avoid performance deterioration, which has been proved challenging. Here we present a scalable growth approach that enables a precise valence state control. By creating an oxygen activity gradient across the wafer, a continuous valence state library is established to directly identify the optimal growth condition. Single-crystalline VO2 thin films have been grown on wafer scale, exhibiting more than four orders of magnitude change in resistivity across the metal-to-insulator transition. It is demonstrated that ‘electronic grade' transition metal oxide films can be realized on a large scale using a combinatorial growth approach, which can be extended to other multivalent oxide systems.
Highlights
Transition metal oxides offer functional properties beyond conventional semiconductors
Phase pure epitaxial VO2 films have been grown by pulsed laser deposition (PLD)[20,21,22], sputtering[23,24,25], molecular beam epitaxy (MBE)[26,27] and chemical solution deposition technique[28], the growth of high-quality VO2 thin films has been found very demanding[21,26], attributed to the complex and rich structural phase diagram of vanadium oxide[5]
This approach has been successfully utilized to optimize the bandgap of III–V semiconductor nanowires[38], discover new luminescent materials[33], study the composition variance of metallic glasses[34], increasing the Curie temperature of the ferromagnetic semiconductor GaMnAs37 and exploring the effect of LaAlO3 cation stoichiometry on electrical properties of the twodimensional electron gas at the LaAlO3/SrTiO3 interface[35]
Summary
Transition metal oxides offer functional properties beyond conventional semiconductors. Such a combinatorial strategy requires (1) precise and direct control of a spatially varying fluxes; (2) two or more sources to independently supply the elements of interest; (3) a favourable deposition geometry, that is, a sufficiently large substrate compared with the flux density profile at sample position to create a sufficiently steep flux gradient; (4) large inelastic mean free path to avoid unintentional gas phase reactions This approach has been successfully utilized to optimize the bandgap of III–V semiconductor nanowires[38], discover new luminescent materials[33], study the composition variance of metallic glasses[34], increasing the Curie temperature of the ferromagnetic semiconductor GaMnAs37 and exploring the effect of LaAlO3 cation stoichiometry on electrical properties of the twodimensional electron gas at the LaAlO3/SrTiO3 interface[35]
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