Broadband MSM photodetector based on S-doped black silicon fabricated by femtosecond laser

Abstract

S-doped black silicon (Si) characterized by high absorption over a wide spectral band, from visible to infrared, is directly processed in ambient air by femtosecond laser irradiation. The S-doped black Si extends the absorption towards infrared range below its bandgap; approximately over 85 % absorptance is achieved in the interval of 1.1 ∼ 2.5 μm even after thermal annealing. Obvious increase in valent state ratio of Si4+ to Si0 is observed by XPS due to the formation of SiO2. Thanks to the passivation effect of SiO2, the background free carrier concentration in the S-doped black Si and the complex structural defects caused by the laser irradiation are effectively reduced, which is beneficial to extend the lifetime of photo-generated carriers as well as improve the thermostability. The metal–semiconductor-metal (MSM) infrared photodetector fabricated by the S-doped black Si shows excellent photosensitivity characteristics: under 1030 nm laser illumination, a responsivity of 367 mA/W@10 V and rising and falling times of 53.82 and 64.51 ms, respectively, are obtained, remarkably outweighing the performance of the unprocessed Si (47 mA/W@10 V) under the same conditions.