应力对蓝宝石衬底上生长二氧化钒薄膜结构和光电性能的调控

doi:10.15541/jim20180045

摘要/Abstract

摘要：

利用脉冲激光沉积技术在蓝宝石衬底上生长不同厚度的VO₂薄膜, 对薄膜的结构、表面形貌和光电性能进行研究。结果表明: 所沉积的VO₂薄膜为具有单晶性能、表面平整的单斜晶相的VO₂薄膜, 相变前后, 方块电阻的变化可达到3~4个数量级, 在波长为2500 nm的透过率变化最高可达56%, 优化的可视透过率(T_lum)和太阳能调节率( ∆T_sol )为43.2%和8.7%。薄膜受到的应力对VO₂薄膜有重要影响, 可以通过调节薄膜的厚度对VO₂薄膜光电性能实现调控。当VO₂薄膜厚度较小时, 薄膜受到拉应力, 拉应力能使相变温度显著降低, 金属-绝缘体转变性能(MIT)不但与载流子浓度的变化相关, 而且还受载流子迁移率变化的影响;当VO₂薄膜厚度较大时, 薄膜受到压应力, VO₂薄膜的相变温度接近块体VO₂的相变温度, MIT转变主要来自于载流子浓度在相变前后的变化, 其载流子迁移率几乎不变。

关键词: 脉冲激光沉积, VO2, 应力, 光电性能

Abstract:

VO₂ thin films with different thicknesses were deposited on sapphire substrates by pulsed laser deposition. Structure, surface morphologies and photoelectric properties of the films were characterized. The results indicated that the Monoclinic-VO₂ thin films deposited on the sapphire substrates were high quality poly-crystalline stoichiometric with no detectable impurities, and the sheet resistance changed up to 3-4 orders of magnitude and the transmittance at 2500 nm up to 56% across metal-insulator transition (MIT). The optimized integral luminous transmittance (T_lum) and solar regulation rate (∆T_sol) were 43.2% and 8.7%, respectively. The stress on the interface had important influence on the VO₂ thin film, and the photoelectric properties of VO₂ thin films could be regulated by adjusting the film thickness. When the VO₂ film was thinner, the film was subjected to tensile stress, which could significantly reduce the phase-change temperature, and the increase of the carrier concentration as well as carrier mobility accounted for the decrease of electrical resistance across the MIT. While the VO₂ film was thicker, the film was subjected to compressive stress and the phase transition temperature of VO₂ film was close to that of body VO₂. The increase of the carrier concentration accounted almost entirely for the decrease of electrical resistance and the change in mobility had little contribution to the MIT.

Key words: pulsed laser deposition, VO2, stress, photoelectric properties

中图分类号:

O484

张聪, 康朝阳, 宗海涛, 李明, 梁珊珊, 曹国华. 应力对蓝宝石衬底上生长二氧化钒薄膜结构和光电性能的调控[J]. 无机材料学报, 2018, 33(11): 1225-1231.

ZHANG Cong, KANG Chao-Yang, ZONG Hai-Tao, LI Ming, LIANG Shan-Shan, CAO Guo-Hua. Stress Induced Modulation of the Structure and Photoelectric Property of Vanadium Oxide Films on Sapphire Substrate[J]. Journal of Inorganic Materials, 2018, 33(11): 1225-1231.

图/表 7

图1 蓝宝石衬底上沉积的不同厚度VO2薄膜的XRD图谱(a)及在38°~43°范围的放大XRD图谱(b)

Fig. 1 (a) XRD patterns and (b) amplified XRD patterns in the range of 38°-43° of the VO2 films with different thicknesses deposited on sapphire substrates

表1 蓝宝石衬底上不同厚度VO2薄膜的VO2 (020)峰位、薄膜应变力及晶粒大小

Table 1 VO2 (020) peaks position, film strain and the grain sizes of the VO2 films with different thicknesses deposited on sapphire substrates

Thickness /nm	VO₂(020) peaks position/(°)	Film stress /MPa	Grain size /nm
10	39.75	402	13.42
30	39.79	67	14.90
60	39.98	-144	16.27
120	40.02	-161	21.15

图2 蓝宝石衬底上沉积的不同厚度VO2薄膜的原子力显微镜照片

Fig. 2 AFM morphologies of VO2 films with different thicknesses deposited on sapphire substrates ^(a) 10 nm; (b) 30 nm; (c) 60 nm; (d) 120 nm

图3 蓝宝石衬底上沉积的不同厚度VO2薄膜在25与90℃的透过率谱图(a)和Tlum(25℃)、Tlum(90℃)与∆Tsol随厚度的变化曲线(b)

Fig. 3 (a) Transmittance spectra at 25℃ and 90℃ for VO2 films with different thicknesses deposited on sapphire substrates and (b) corresponding variation curves of Tlum(25℃), Tlum(90℃) and ∆Tsol with thickness

图4 蓝宝石衬底上沉积不同厚度的VO2薄膜在2500 nm处透过率随温度变化的热滞回线, 插图为各自的微分曲线

Fig. 4 Thermal hysteresis loops of optical transmittance at 2500 nm for VO2 films with different thicknesses deposited on sapphire substrates, with insets showing the corresponding differential curves

图5 蓝宝石衬底上沉积不同厚度VO2薄膜的方块电阻的热滞回线

Fig. 5 Thermal hysteresis loops of sheet resistance for VO2 films with different thicknesses deposited on sapphire substrates

图6 蓝宝石衬底上沉积不同厚度VO2薄膜的载流子浓度与载流子迁移率随温度的变化曲线

Fig. 6 Temperature dependent carrier density and mobility curves of VO2 films with different thicknesses deposited on sapphire substrates

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