Laser Fabricating Micro-Nano Structures in Optoelectronic Devices

01 Introduction
Micro/nanostructures refer to engineered structures with unique dimensions, hierarchies, and properties distinct from bulk materials. Over the past 20 years, they have become indispensable across various application fields. Integrating micro/nanostructures inside or outside optoelectronic devices can significantly enhance their performance. These structures improve light absorption and the efficiency of surface plasmon polaritons in optoelectronic devices. Laser-based fabrication of micro/nanostructures for optoelectronics enables broadband, transparent, anti-reflective surfaces with high efficiency, precision, and minimal thermal effects. As laser technology can achieve specific and unique optical and electronic properties, it has become a key component in the field of optoelectronics.

02 Photodetectors
Photodetectors are devices that convert incident light signals into electrical signals and have been explored in many applications such as temperature monitoring, thermal imaging, and optical communication systems. Laser-fabricated micro/nanostructures can enhance the performance of photodetectors by optimizing light-matter interaction. For instance, F.H. Alkallas et al. presented a study on the fabrication of CdS/Si photodetector devices using pulsed laser ablation in a DMSO solution. Considering the influence of the liquid medium in laser ablation, they investigated the photodetection characteristics of the heterojunction. Cd targets were ablated in DMSO while stirring to promote the formation of CdS nanoropes, which were then deposited onto Si substrates via spin coating. CdS, a direct bandgap II-VI semiconductor with a gap of 2.42 eV, is widely used in transistors, sensors, and photodetectors for its excellent optoelectronic properties. Their research highlighted the excellent linearity of CdS-based photodetectors, significantly improving light detection performance.

Figure 1. Schematic diagram of CdS/Si heterojunction formation by assisted pulsed laser ablation and spin coating. (a, b) TEM images of fabricated CdS nanorope and its EDX analysis, and (c, d) schematic diagram and SEM images of CdS nanorope deposited on Si substrate from thickness and top surface.

03 Photovoltaics
Photovoltaics provide a practical and effective solution to the growing global energy demand. The technology converts solar energy into electricity, offering a sustainable and renewable energy alternative. H. Yang et al. proposed a novel method for processing micro/nanostructures on Cu(In,Ga)Se₂ (CIGS)/ITO bilayer thin films to broaden their application in the solar cell industry. CIGS thin films are widely recognized in photovoltaic applications due to their high efficiency as direct bandgap semiconductors, with absorption thicknesses of 1–2 μm and absorption coefficients up to 10⁵ cm⁻¹. Various manufacturing techniques alter the elemental composition of these films, thus affecting their efficiency. In this study, researchers used femtosecond laser fabrication to create controlled micro/nanostructures and employed ultrafast laser processing to achieve unique material characteristics. To analyze interactions between the CIGS/ITO bilayers and the laser, they studied field strength at different layer positions and fabricated structures by varying laser parameters such as scan speed and pulse energy. Interactions among ultrafast photons, electrons, and phonons enabled precise control over periodic structural morphology by fine-tuning the processing parameters during laser exposure.

Figure 2. Schematic diagram of processing: laser irradiation of CIGS/ITO bilayer film perpendicular to its surface, scanning direction parallel to laser polarization and fabrication of micro-nanostructures.

04 Light-Emitting Diodes (LEDs)
Light-emitting diodes (LEDs) are semiconductor diodes that emit energy when current flows through them, converting electrical energy into light—essentially the reverse of photovoltaics. C. Liu et al. conducted a study analyzing the optoelectronic characteristics of micro-LEDs before and after the laser lift-off (LLO) process. LLO has been recognized as a crucial technique for integrating micro-LEDs into display modules. They applied this process to high-performance gallium nitride (GaN)-based green micro-LED arrays with pixel sizes of 20×38 μm on patterned sapphire substrates (PSS). Ultraviolet lasers were chosen for the LLO process because the photon energy of the UV source surpasses the GaN bandgap but remains below the sapphire bandgap. Selective absorption of laser energy by the GaN layer causes rapid interface heating, exceeding the thermal delamination threshold, resulting in GaN decomposition into nitrogen gas (N₂) and low-melting-point gallium metal. After the LLO process, the light output power and external quantum efficiency of the micro-LEDs were significantly enhanced.

Figure 3. I. (a) Schematic diagram of micro-LED, (b) fabricated micro-LED array using scanning electron microscopy morphology, (c) schematic diagram of physical mechanism of LLO process. II. Scanning electron microscopy morphology after LLO: (a) LLO and LLO-free area; (b) sapphire substrate after LLO; (c) bottom of a single micro-LED after LLO; (d) area without micro LED after LLO.

05 Conclusion
The flexibility of laser technology has been applied to various fields, enabling the fabrication of micro/nanostructures without the need for complex techniques such as photolithography. This enhances design versatility, especially in optoelectronic devices, supporting the development of semiconductors for photodetectors, photovoltaics, sensors, biosensors, and LEDs—thus improving their efficiency and performance. In summary, laser-fabricated micro/nanostructures have become an indispensable technology driving advancements in optoelectronic devices.

**--Cite the article published by 高能束加工技术 on June 27, 2025, in the WeChat public account "High-Energy Beam Processing Technology and Applications."