Comparative Study of Plasma-Enhanced-Atomic-Layer-Deposited Al2O3/HfO2/SiO2 and HfO2/Al2O3/SiO2 Tri-Layers for Ultraviolet Laser Applications

High-performance thin films combining large optical bandgap Al2O3 and high refractive index HfO2 are excellent components for constructing the next generation of laser systems with enhanced output power. However, the growth of low-defect plasma-enhanced-atomic-layer-deposited (PEALD) Al2O3 for high-power laser applications, and its combination with HfO2 and SiO2 materials commonly used in high-power laser thin films still face challenges, such as how to minimize defects, especially interface defects. In this work, substrate-layer interface defects in Al2O3 single-layer thin films, layer-layer interface defects in Al2O3-based bilayer and tri-layer thin films, and their effects on the laser-induced damage threshold (LIDT) were investigated via capacitance-voltage (C-V) measurements. The experimental results show that by optimizing the deposition parameters, specifically the deposition temperature, precursor exposure time, and plasma oxygen exposure time, Al2O3 thin films with low defect density and high LIDT can be obtained. Two tri-layer anti-reflection (AR) thin film structures, Al2O3/HfO2/SiO2 and HfO2/Al2O3/SiO2, were then prepared and compared. The tri-layer AR thin film with Al2O3/HfO2/SiO2 structure exhibits a lower interface defect density, better interface bonding performance, and an increase in LIDT by approximately 2.8 times. We believe these results provide guidance for the control of interface defects and the design of thin film structures and will benefit many thin film optics for laser applications.结合了大光学带隙氧化铝（Al2O3）与高折射率二氧化铪（HfO2）的高性能薄膜，是构建输出功率增强型下一代激光系统的优质元件。然而，面向高功率激光应用的低缺陷等离子体增强原子层沉积（PEALD）氧化铝薄膜的制备，以及其与高功率激光薄膜常用的二氧化硅（SiO2）、二氧化铪（HfO2）材料的复合，仍面临诸多挑战，例如如何最大限度降低缺陷，尤其是界面缺陷。本研究通过电容-电压（C-V）测试手段，探究了氧化铝单层薄膜的衬底-薄膜界面缺陷、基于氧化铝的双层及三层薄膜的层间界面缺陷，及其对激光诱导损伤阈值（LIDT）的影响。实验结果表明，通过优化沉积参数——具体为沉积温度、前驱体曝露时间与等离子体氧气曝露时间，可获得缺陷密度低且激光诱导损伤阈值高的氧化铝薄膜。随后制备并对比了两种抗反射（AR）三层薄膜结构：Al2O3/HfO2/SiO2与HfO2/Al2O3/SiO2。采用Al2O3/HfO2/SiO2结构的三层抗反射薄膜，展现出更低的界面缺陷密度、更优异的界面结合性能，且激光诱导损伤阈值提升约2.8倍。我们认为，本研究结果可为界面缺陷调控与薄膜结构设计提供指导，并将惠及众多面向激光应用的薄膜光学器件。