Research On Preparation And Phase Transition Properties In The Terahertz Band Of Vanadium Oxide Thin Films

Vanadium dioxide?VO₂?thin film has good thermal insulator-metal transition?MIT?in the terahertz?THz?band,which makes VO₂ a promising candidate for a variety of applications,such as photoelectric switch,terahertz modulation,memory devices and so on.Across the transition of VO₂,the optical transmission in the terahertz band undergoes a large mutation.At room temperature,the VO₂ thin film is in the semiconductor state,and the THz wave has no absorption and dispersion,and the THz transmittance is high.However,as the temperature increases beyond the transition temperature,the VO₂ film transforms into a metallic state,and the THz transmittance of the film is drastically reduced.We can acheive terahertz modulation by controling the phase transition of the vanadium dioxide thin film,which the terahertz wave is in two different states of transmission and non-transmission.The phase transition could be triggered by not only temperature,but also electrical field and optical excitation.The phase transition properties of VO₂ thin films in the THz band are favorable for the study and preparation of THz-modulating devices with ultra-high speed,high modulation depth and working near room temperature,which filling THz band lacks the control material and device defects,having important scientific significance and application value.In order to realize the application of vanadium dioxide thin film on terahertz modulation device,it is required that the vanadium dioxide thin film has good stability and reliability,high response rate and efficiency.VO₂ should meet the performance requirements of four aspects:?1?a high THz transmittance before phase change;?2?large amplitude modulation depth;?3?small hysteresis width;?4?low transition temperature.This paper mainly focuses on the development of vanadium dioxide thin films with good terahertz modulation performance.Based on the lack of high modulation range vanadium dioxide thin films at this stage,the following two parts are carried out:?1?The vanadium dioxide thin films were deposited on high-purity single-crystal Si?100?substrate??10 000 ?·cm,500 ?m?by DC reactive magnetron sputtering,investigating the effects of process parameters?reaction oxygen flow rate and sputtering current?on the MIT performance.In the experiment,we found that the surface state of target also affect the MIT performance of vanadium dioxide,especially the transition amplitude modulation depth.Furthermore,the influence of the the surface state of target on the MIT performance of the vanadium dioxide thin film was studied.The vanadium dioxide thin film prepared on the flat target has average amplitude modulation depth range of 93% in the 4.8 6THz,which the THz transmittance before phase change is about 87% and after phase change is about 6%,?2?The vanadium dioxide thin film prepared on the flat target has a high amplitude modulation depth in the 4.8 6THz band,but the hysteresis width of the film is wide?12.4??and the transition temperature is high?67.5??,which can not fully meet the four performance requirements,so we use doping?Mo and W?to reduce the film's hysteresis width and transition temperature.The vanadium dioxide thin film with low hysteresis width?7.7??and low transition temperature?49.1??was prepared by doping W?1.5at.%?,while maintaining excellent terahertz modulation amplitude depth?4.8⁶THz,83%?.