Room Temperature Optical Constants and Band Gap Evolution of Phase Pure M1-VO2Thin Films Deposited at Different Oxygen Partial Pressures by Reactive Magnetron Sputtering

Meng Jiang,Ping Jin,Yanfeng Gao,Yamei Li,Shaotang Li,Xun Cao,Huaijuan Zhou,Hongjie Luo,Shanhu Bao

doi:10.1155/2014/183954

Abstract

Spectroscopic ellipsometry study was employed for phase pure VO2(M1) thin films grown at different oxygen partial pressures by reactive magnetron sputtering. The optical constants of the VO2(M1) thin films have been determined in a photon energy range between 0.73 and 5.05 eV. The near-infrared extinction coefficient and optical conductivity of VO2(M1) thin films rapidly increase with decreasing O2-Ar ratios. Moreover, two electronic transitions can be uniquely assigned. The energy gaps correlated with absorption edge(E1)at varied O2-Ar ratios are almost the same (~2.0 eV); consequently, the absorption edge is not significantly changed. However, the optical band gap corresponding to semiconductor-to-metal phase transition(E2)decreases from 0.53 to 0.18 eV with decreasing O2-Ar ratios.

Highlights

IntroductionVO2 has a tetragonal rutile structure with the P42/mnm space group (R phase) above the phase transition temperature, where the partially filled d// band localized at the Fermi level and the rutile phase is metallic [2]
Vanadium dioxide (VO2), one of the most interesting transition metal oxides, exhibits a reversible first-order semiconductor-to-metal phase transition (SMT) at a critical temperature Tc = 68∘C [1]
The optimized oxygen partial pressure to fabricate VO2 films on glass and the optical properties of those samples were investigated [8], the optical constants, especially extinction coefficient k, which is crucial in understanding band structures, are not involved

Summary

Introduction

VO2 has a tetragonal rutile structure with the P42/mnm space group (R phase) above the phase transition temperature, where the partially filled d// band localized at the Fermi level and the rutile phase is metallic [2]. It has been noted that oxygen partial pressure has effects on the structural and resistivity transition behaviors of VO2 [7]. The optimized oxygen partial pressure to fabricate VO2 films on glass and the optical properties of those samples were investigated [8], the optical constants, especially extinction coefficient k, which is crucial in understanding band structures, are not involved. Two electronic transitions related to absorption edge (E1) and SMT (E2) were distinguished

Experimental Section

Results and Discussion

Conclusions