Issue |
EPL
Volume 109, Number 2, January 2015
|
|
---|---|---|
Article Number | 27004 | |
Number of page(s) | 6 | |
Section | Condensed Matter: Electronic Structure, Electrical, Magnetic and Optical Properties | |
DOI | https://doi.org/10.1209/0295-5075/109/27004 | |
Published online | 02 February 2015 |
Unusual M2-mediated metal-insulator transition in epitaxial VO2 thin films on GaN substrates
1 Department of Physics, Sungkyunkwan University - Suwon 440-746, Republic of Korea
2 Department of Engineering Science, University of Oxford - Parks Road, Oxford, OX1 3PJ, UK
3 Department of Information & Communication Engineering, Daegu Gyeongbuk Institute of Science & Technology Daegu 711-873, Republic of Korea
(a) djkang@skku.edu (corresponding author)
Received: 19 November 2014
Accepted: 10 January 2015
We report on the epitaxial growth of vanadium dioxide $(\text{VO}_{2})$ thin films on (0001) GaN substrates using a radio frequency magnetron sputtering method and discuss their unusual M2-mediated metal-insulator transition (MIT) properties. We found that large lattice misfits between the $\text{VO}_{2}$ film and the GaN substrate could favor the stabilization of the intermediate insulating $\text{M}_{2}$ phase, which is known to be observed only in either doped or uniaxially strained samples. We demonstrated that the MIT in $\text{VO}_{2}$ films on GaN substrates could be mediated via a monoclinic $\text{M}_{2}$ phase during the transition from a monoclinic $\text{M}_{1}$ to a rutile R phase. This was confirmed by temperature-dependent Raman studies that exhibited both an evident upshift of a high-frequency phonon mode $(\omega_{\text{V-O}})$ from $618\ \text{cm}^{-1}\ (\text{M}_{1})$ to $645\ \text{cm}^{-1}\ (\text{M}_{2})$ and a distinct peak splitting of a low-frequency phonon mode $(\omega_{\text{V-V}})$ at $221\ \text{cm}^{-1}\ (\text{M}_{2})$ for increasing temperatures. Moreover, a resistance change of four orders of magnitude was observed for $\text{VO}_{2}$ thin films on GaN substrates, being indicative of the high quality of $\text{VO}_{2}$ thin films. This study may offer great opportunities not only to improve the understanding of M2-mediated MIT behavior in $\text{VO}_{2}$ thin films, but also to realize novel electronic and optoelectronic devices.
PACS: 71.30.+h – Metal-insulator transitions and other electronic transitions / 64.70.Nd – Structural transitions in nanoscale materials / 78.20.-e – Optical properties of bulk materials and thin films
© EPLA, 2015
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