Broadband optical absorption copper surface fabricated by femtosecond laser for sensitivity enhancement of thermoelectric photodetector

The limited sensitivity and inherent long response time restrict the widespread applicability of thermally-based photodetectors. Herein, a copper surface endowed with optical absorption enhancement by femtosecond laser fabrication is introduced, to improve the sensitivity and power prediction speed of thermoelectric photodetectors. Cross-scale microstructures including periodic micro-taper array and randomly dispersed particles are obtained on the surface, and their formation mechanism is elucidated. The surface exhibits an average reflectivity of 8% over the wavelength range of 200–2500 nm. This broadband absorption is mainly due to the local light field enhancement by the unevenly oxidized and size-dispersed particles, while the periodic micro-taper array further enhances the absorption by geometric light trapping effect. When integrated into a thermoelectric device, a comprehensive parameter analysis including sensitivity (45.053 mV/W), response time (5.47 s), precision of time-dependent prediction (2 s to obtain R2⩾0.999), and precision of measuring at different points (3.97%) is performed. Our study offers a practical approach to produce cross-scale light absorption microstructure, paving the way for its promising advances in photothermal-based optoelectronic applications.