Heterojunction-Type Hydrogen Sensor Based on Silicon Nanoconvexity Induced by Femtosecond Laser

Simple CuO-based hydrogen sensors at room temperature usually need to be used with precious metals. In this work, a p -CuO/ n -Si hydrogen sensor with a nanoconvexity structure is conceived as an effective room-temperature hydrogen sensor without the precious metal decoration. The convexity-like nanostructure was induced on the n -Si substrate surface using the femtosecond (fs) laser direct writing technique. After hydrofluoric acid (HF) treatment, a layer of a p -CuO nanofilm was sputtered to fabricate a pn-junction hydrogen sensor (CuO/fs-Si). The sensor can work at room temperature when hydrogen concentration ranges from 100 to 30,000 ppm. At a hydrogen concentration of 10,000 ppm, the response time constant is 216 s. As a comparison, it is found that a pn-junction-type CuO/Si sensor without fs laser processing (CuO/Si) cannot detect hydrogen with a concentration of less than 10,000 ppm. The nanostructured Si surface improves the sensitivity of the sensor and reduces the detection limit. Operating at room temperature reduces the energy consumption of the sensor and improves applicability. A simple p -CuO/ n -Si bilayer structure provides an alternative idea to develop miniaturized, low-power, compatible, and integrated hydrogen sensors.