Patterning of layered semiconductor GeS₂ by laser photooxidation and water immersion

Common patterning methods, such as lithography and laser ablation, have detrimental effects on electronic device components because of lithographic-resist residues and laser-induced heat. These effects are particularly significant in two-dimensional layered materials owing to their ultimate thinness. In this study, a lithography-free patterning method was developed using a laser power lower than that required for laser ablation. This method is based on laser photooxidation and the subsequent etching of the formed oxide. Laser irradiation of exfoliated flakes of GeS₂-a layered semiconductor-and subsequent immersion in water form etched holes with diameters close to the diffraction limit of the irradiated light. The required laser power was 200 times lower than that required for laser ablation, which could significantly mitigate the heat-induced damage. Furthermore, the use of water as an etchant demonstrated the environmentally friendly nature of this method. The proposed method is applicable to materials whose photooxides are soluble in water, and the patterning accuracy can be improved using short-wavelength light and a highly stable mechanical stage.