Metal assisted chemical etching for high aspect ratio nanostructures: A review of characteristics and applications in photovoltaics

► Metal assisted chemical etching (MacEtch) is a wet but directional etching method. ► Aspect ratio and morphology depend on metal catalyst, semiconductor, and etchants. ► Si nanostructures with extremely high aspect ratio can be achieved by MacEtch. ► MacEtch also works for non-Si based semiconductors. ► MacEtch produced structures are promising for photovoltaic applications.