Speaker
Description
Vanadium oxide (VOX) thin films of different phase composition and stoichiometry (1.5< x< 2.5) are widely used in nano- and micro-electronics, sensors, applied optics, and energy-saving technologies. There are about 20 phases of vanadium-oxygen system including main (VO, V2O3, V3O5, VO2, V2O5) and defective (VnO2n-1, VnO2n+1, etc) phases. Of particular interest are the VO2 phase, which have rapid reversible metal-insulator phase transition (MIT). The main issue is the simultaneous formation of different phases during VOx thin film growth. Therefore, despite the experience of several decades, during which many methods of synthesis of VO2 and other useful phases of VOx were developed, the problem of obtaining precisely the target phase, not only of a given stoichiometry (x=2) still remains. Accumulated experience has shown that, mainly, it is not possible to synthesize a VOX film of the required stoichiometry, phase composition and crystal structure in one step. To form a film with one dominant phase the usage of corrective post-treatments, like post low temperature annealing (under 450 oC) which leading to VO2 phase crystallisation in amorphous VOx films.
This work presents a new method of post-growth control of oxygen content in VOx thin films by gettering. It is implemented through an ultrathin intermediate aluminium layer deposited on the substrate before the VOx film deposition. During annealing the system in an inert environment, gradual diffusion of oxygen from the VOx film towards Al and its oxidation takes place. The 200 nm VOₓ/Al/Si heterosystem was subject to thermodynamic analysis and investigated experimentally. The films were deposited by reactive RF magnetron sputtering using O2/Ar gas mixture, followed by annealing in Ar atmosphere. The crystalline structure of VOx thin films was investigated using X-Ray diffraction. The chemical state of the surface was analysed using X-Ray photoelectron spectroscopy. The redistribution of elemental composition in VOₓ>₂/Al heterostructures during thermal oxygen gettering were investigated using secondary ion mass spectrometry (SIMS) depth profiling. A new cluster-ion analysis of VOx films was proposed. The results show that gettering promoted the V₂O₅-to-VO₂ transformation and incorporated Al as bridging Al–O–Al complexes replacing V–V dimers.
This work was partly supported by priority research program of NAS of Ukraine, project #0125U000799 “New physical principles and technologies for the development of the component base of modern infrared optoelectronics”