Ma Hao, Zhao Yuan'an, Shao Yuchen, Lin Xiangkun, Li Dawei, Cao Zhaoliang, Leng Yuxin, Shao Jianda
Opt Express. 2021 Nov 8;29(23):38591-38605. doi: 10.1364/OE.442882.
In recent years, there has been increasing interest in optoelectronic applications of transparent conductive oxide (TCO) thin-film-based materials and devices fabricated using patterning techniques. Meanwhile, femtosecond laser processing is a convenient method that further improves the performance of TCO-based functional devices and expands their application prospects. In this study, we proposed a simple and effective strategy to determine the fluences required for laser processing TCOs. We investigated the modification of an indium tin oxide (ITO) film induced by a femtosecond laser (45/150 fs, 800 nm) at different pulse fluences. The results reveal that the laser modification of ITO films is highly dependent on the irradiated pulse fluences. Several distinct types of final micro/nanostructures were observed and may be attributed to superficial amorphization, spallation ablation, stress-assisted delamination, boiling evaporation, and phase explosion. The final micro/nanostructures were studied in detail using optical microscopy, scanning electron microscopy, transmission electron microscopy and a surface profiler. At a lower fluence above the melting but below the ablation threshold, a laterally parabolic amorphous layer profiled with maximum thicknesses of several tens of nanometers was quantitatively attained. At a higher fluence, stress-assisted delamination and superheated liquid-induced micro-honeycomb structures emerged. Furthermore, the electron and lattice temperature evolutions were also obtained using a two-temperature model to prove the ablation mechanism and ascertain the micro/nanostructure formation principle. The predicted surface temperatures confirmed film amorphization without ablation below 0.23 J/cm. These results reveal the interaction mechanism between femtosecond laser pulse and ITO film including the competition between the free electron heating of intraband transition and the multiphoton absorption of the interband transition, which promotes the potential applications for femtosecond laser processing TCO films and other wide-band-gap semiconductors such as photodetectors, solar cells, UV-light-emitting diodes, and flat-panel displays.
近年来，人们对基于透明导电氧化物（TCO）薄膜的材料及采用图案化技术制造的器件的光电应用兴趣日益浓厚。同时，飞秒激光加工是一种便捷的方法，可进一步提升基于TCO的功能器件的性能并拓展其应用前景。在本研究中，我们提出了一种简单有效的策略来确定激光加工TCO所需的能量密度。我们研究了飞秒激光（45/150 fs，800 nm）在不同脉冲能量密度下对氧化铟锡（ITO）薄膜的改性。结果表明，ITO薄膜的激光改性高度依赖于辐照脉冲能量密度。观察到了几种不同类型的最终微/纳米结构，这可能归因于表面非晶化、剥落烧蚀、应力辅助分层、沸腾蒸发和相爆炸。使用光学显微镜、扫描电子显微镜、透射电子显微镜和表面轮廓仪对最终的微/纳米结构进行了详细研究。在高于熔点但低于烧蚀阈值的较低能量密度下，定量获得了横向呈抛物线形、最大厚度为几十纳米的非晶层。在较高能量密度下，出现了应力辅助分层和过热液体诱导的微蜂窝结构。此外，还使用双温度模型获得了电子和晶格温度的演变，以证明烧蚀机制并确定微/纳米结构的形成原理。预测的表面温度证实，在0.23 J/cm²以下时薄膜发生非晶化而无烧蚀。这些结果揭示了飞秒激光脉冲与ITO薄膜之间的相互作用机制，包括带内跃迁的自由电子加热与带间跃迁的多光子吸收之间的竞争，这推动了飞秒激光加工TCO薄膜以及其他宽带隙半导体（如光电探测器、太阳能电池、紫外发光二极管和平板显示器）的潜在应用。
