Enhancing light trapping of macroporous silicon by alkaline etching: application for the fabrication of black Si nanospike arrays

The synthesis of highly absorbing silicon (black Si (BSi)) is a very active research topic with promising applications in the field of sustainable energies, ultrasensitive sensing and antibacterial materials. Here, we show that extended alkaline etching of macroporous Si, fabricated by photoelectrochemical etching, drastically influences the surface structures as well as their optical properties. We demonstrate that this treatment can considerably improve the light trapping of the surface and we finally show that it is possible to use it for fabricating very quickly highly- absorbing arrays of sharp and crystalline BSi nanospikes (NSpikes).