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Strain engineering allows researchers to alter a material's electronic and optical behavior by changing its physical structure rather than its chemical composition. The approach is well established in crystalline materials, whose ordered atomic lattices respond predictably to deformation. Applying the same principle to amorphous materials is more difficult. Their atoms lack long-range order, and conventional thermal or mechanical treatments can cause crystallization, cracking, elemental segregation or damage at material interfaces.

As reported in Advanced Photonics, researchers led by Heping Zeng at East China Normal University recently developed a laser-based approach for modifying an amorphous semiconductor while preserving its predominantly disordered structure.

The method uses programmable sequences of femtosecond laser pulses to generate localized mechanical stress. The researchers call the approach "digital cold strain engineering," or DCSE.

The method is "digital" because the processing condition is controlled by changing the integer number of sub-pulses within each laser burst. It is described as "cold" because the femtosecond pulses deposit energy faster than it can initially diffuse through the material. This limits early thermal spreading, although it does not mean that the process is entirely free of heat.

The researchers tested DCSE on thin films of amorphous gallium oxide, or a-Ga₂O₃. This wide-bandgap semiconductor is of particular interest for solar-blind ultraviolet photodetectors, which detect UV wavelengths that are largely absorbed by Earth's atmosphere and therefore encounter little background from sunlight at ground level.

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