Properties investigation of crystalline silicon surface irradiated by nanosecond laser pulses in different background atmospheres

Abstract

Black silicon materials were obtained by irradiation with ns laser pulses in different ambient atmospheres. The surface morphology, optical properties, and electrical properties of the black silicon were investigated after the ablation by ns laser pulses. Slab-like structures and boundaries were formed on the surface of black silicon fabricated in sulfur hexafluoride (SF6), argon (Ar), and vacuum. In addition, a micrometer-sized sphere was observed at the tip of the slab-like structure, which was not obvious for the black silicon prepared in oxygen (O2), nitrogen (N2), and air. The infrared absorption of all the black silicon materials was enhanced. For the two samples fabricated in SF6 and Ar, the infrared absorptance was approximately 50% at 1500 nm. A post-thermal annealing process decreased the infrared absorptance of all the black silicon materials except for that prepared in SF6. The sheet resistance of the black silicon was reduced by the ns laser irradiation process, and thermal annealing further decreased the sheet resistance of all the samples except for the one fabricated in SF6. After annealing at 875 K, the sheet carrier density of the black silicon fabricated in an Ar atmosphere and vacuum was approximately 1013 cm−2, which was approximately three orders of magnitude larger than that of the silicon substrate (1010 cm−2). The large difference in carrier density between the black silicon layer and substrate is beneficial for establishing contact junctions and for application in infrared photodetection.