Japanese scientists develop ultra-fast laser structure technology, which can replace lithography technology to produce transistors

Scientists have demonstrated how the laser-induced periodic surface structure (LIPSS) changes with laser properties.

This achievement published in the Scientific Reports is conducive to promoting the wide application of LIPSS to realize the simple, economical and easily accessible nanostructure surface manufacturing in the production of optoelectronic devices.

The ability to create structures on the sub-micron scale is crucial for the production of transistors and other components for optoelectronic devices - these devices are also shrinking as the demand for additional computing power, storage and energy efficiency increases. At present, this kind of manufacturing is solved by photolithography and electron beam lithography. However, these methods are usually complex and extremely expensive, and are not easy to apply in practice, requiring high-level professional knowledge.

(Image source: Nagoya Institute of Technology)
In recent years, LIPSS has become a novel and promising alternative method. In this method, femtosecond laser is used to transmit ultrashort laser pulses, which spontaneously lead to the formation of periodic patterns on the surface that are much smaller than the laser wavelength.

In order to achieve more standardized LIPSS production, it is important to understand how the laser source used affects the quality of the formed surface structure, that is, according to the crystallinity of the substrate and the potential possibility of defects and strains.

In order to achieve this goal, the Nagoya Institute of Technology of Japan led the cooperation with Osaka University, Tokai University, Kyoto University and Japan Atomic Energy Agency (JAEA) to directly study various parameters affected by the selection of laser sources.

Scientists have used two different femtosecond lasers on silicon substrate (note: silicon substrate is a material widely used in optoelectronic devices). In one experiment, a wavelength of 0.8 was used μ M Ti: Sapphire laser builds silicon in a way higher than the bandgap energy. In another experiment, a wavelength of 11.4 was used μ M (middle infrared) free electron laser can detect the effect when the energy is lower than the sample band gap energy.

They carried out microscopic and macroscopic analysis on the prepared LIPSS samples. The crystallinity and purity were studied by transmission electron microscopy (TEM), and the stability of the wider structure was studied by synchrotron high-energy X-ray diffraction.

Dr. Reina Miyagawa of Nagoya University of Technology said: "When using a Ti: Sapphire laser, the LIPSS observed retains the high crystal properties of silicon, but seems to bear some residual strain. In contrast, the LIPSS formed by a mid-infrared free-electron laser causes some clearly visible defects. However, the system does not have any observable pressure."

The research results show that LIPSS can be tuned and customized to adapt to specific applications through proper laser selection and by controlling its defects, strain and periodicity. According to the researchers, further research along these directions will further open the way for the wide application of LIPSS to achieve low-cost, simple and easy-to-manufacture nanostructured surfaces, which can be applied to a wide range of optoelectronic devices.

Source: OFweek