Controlling metal–insulator transitions in reactively sputtered vanadium sesquioxide thin films through structure and stoichiometry

Abstract

We present a study of $$\hbox {V}_{2}\hbox {O}_{3}$$ V 2 O 3 thin films grown on c-plane $$\hbox {Al}_{2}\hbox {O}_{3}$$ Al 2 O 3 substrates by reactive dc-magnetron sputtering. Our results reveal three distinct types of films displaying different metal–insulator transitions dependent on the growth conditions. We observe a clear temperature window, spanning 200 $$^{\circ }$$ ∘ C, where highly epitaxial films of $$\hbox {V}_{2}\hbox {O}_{3}$$ V 2 O 3 can be obtained wherein the transition can be tuned by controlling the amount of interstitial oxygen in the films through the deposition conditions. Although small structural variations are observed within this window, large differences are observed in the electrical properties of the films with strong differences in the magnitude and temperature of the metal–insulator transition which we attribute to small changes in the stoichiometry and local strain in the films. Altering the sputtering power we are able to tune the characteristics of the metal–insulator transition suppressing and shifting the transition to lower temperatures as the power is reduced. Combined results for all the films fabricated for the study show a preferential increase in the a lattice parameter and reduction in the c lattice parameter with reduced deposition temperature with the film deviating from a constant volume unit cell to a higher volume.

Structural and electrical properties of V2O3 thin films on c-plane Al2O3 fabricated by reactive-HiPIMS and dcMS techniques

“…The coherence length as a function of f R is also presented in figure 2(d). The above analysis of the epitaxial quality of films is in good agreement with the data obtained via reciprocal space mapping and the phi-scan profiles (not shown here) and has already been explored in our earlier work over similar structures [10,30], fabricated via dcMS sputtering.…”

“…Figure 2(b) shows XRD scans for varying O 2 flow rates for the dcMS deposited films, at constant power of 150 and 200 W. The epitaxial nature obtained by dcMS deposition is found to be strictly dependent on both the power setting and specific O 2 flow rate [10]. That is, films deposited at 200 W with a 1.5 sccm O 2 flow rate showed similar structural quality (epitaxial nature) as that obtained at a lower power and O 2 flow setting of 150 W and 1.0 sccm, respectively.…”

“…That is, films deposited at 200 W with a 1.5 sccm O 2 flow rate showed similar structural quality (epitaxial nature) as that obtained at a lower power and O 2 flow setting of 150 W and 1.0 sccm, respectively. A detailed description for varying dcMS power can be found elsewhere [5,10]. However, it is worth mentioning here that, in dcMS the reactive sputtering operational window (i.e.…”

“…In contrast, chromium doping increases the T MIT and can create a paramagnetic insulating phase near room temperature (RT) [3,8] or alternatively can promote excess of oxygen in films, stabilizing the metallic state [5,9]. Apart from doping, for V 2 O 3 films deposited on single crystalline substrates the choice of deposition method and fabrication conditions, substrate material and film thickness can also alter the MIT properties [1,10]. Films with varying transport properties have been fabricated where the change in MIT magnitude and T MIT have been correlated to strain induced by lattice mismatch, c/a ratio, film thickness and by altering the stoichiometric composition of the film (as the transition is sensitive to vanadium and oxygen vacancies and/or interstitials) [7,11].…”

Reversible exchange bias in epitaxial V2O3/Ni hybrid magnetic heterostructures

“…Such highly crystalline hybrid heterostructures of this type have not been reported previously in the literature. Previously, we have shown that the epitaxial nature of V 2 O 3 films grown by dc-magnetron sputtering is strongly dependent on the power settings, O 2 flow rate and other deposition parameters [21]. These results reveal the film layering to be extremely well defined with very low roughness.…”