The metal-assisted chemical etching (MACE) of silicon-based substrates can fabricate nanostructures for various energy applications. The drawback of using copper as a replacement for noble metals in MACE (i.e. Cu-ACE) is the self-dissolution of Cu during processing. However, the implementation of two-step processing, including electroless metal deposition and oxidant (H2O2)–assisted hydrofluoric etching, solves the issue. Here, we determined that when p ++ -type silicon was applied in the Cu-ACE process, a photoluminescent silicon layer appeared on the etched surface. This result was surprising because photoluminescent silicon is fairly difficult to achieve with regular MACE processing and p ++-type silicon is also unsuitable for MACE processing, even when used as an ‘etch-stop’ substrate. On the other hand, when using ultraviolet (UV) irradiation with Cu-ACE, a blackened silicon surface, rather than photoluminescent silicon, developed. Here, we demonstrate a technique for either producing a photoluminescent silicon surface or blackening the silicon surface by single Cu-ACE processing. Cu-ACE processing can be developed into a cost-efficient production technology for silicon-based energy applications, such as silicon photonics and silicon solar cells.