The Optical and Electrical Properties of Co-Doped Black Silicon Textured by a Femtosecond Laser and Its Application to Infrared Light Sensing

Co-doped black silicon with sulfur and nitrogen impurities was fabricated by a femtosecond laser in a mixed atmosphere of N
₂
and SF
₆
. Compared with sulfur-doped black silicon, the infrared absorption of co-doped black silicon shows excellent thermal stability, indicating that the high absorption below the band-gap of silicon is insensitive to the thermal annealing process. According to the electronic nature of annealed co-doped black silicon by the Hall-effect measurement, the sheet carrier density decreases with increasing nitrogen content as a result of the neutral doping of the nitrogen pair defect. Furthermore, a near-infrared black silicon photodiode was produced based on the performance of the stable absorption for thermal annealing and its superior photo-response, in which 58 mA/W is obtained for the photodiode for a 1.31-μm detection light.