Investigation of the structure and optical absorption of silicon coated with a chromium film after femtosecond laser irradiation

摘要： Microstructured silicon (Si) doped with chromium (Cr) has been produced by femtosecond laser pulses. Microstructured surfaces were produced after laser irradiation at different fluence values. The dependence of its absorptance on laser fluence and thermal annealing were investigated. Microstructured Si that was fabricated at lower laser fluences exhibited perfect absorption below the Si bandgap as well as better thermal stability. The crystal structures of samples obtained before and after thermal annealing were characterized by Raman spectroscopy. The mechanism of absorption below the bandgap of Si is discussed in detail based on the results from Raman spectroscopy and optical absorption.