Silicon nanowires with mesopores: Fabrication and optical properties

Silicon nanowires (SiNWs) are electrochemically porosified to generate mesopores in sizes of 2-50 nm, resulting in the creation of mesoporous silicon nanowires (mpSiNWs). The porosification imposes two characteristics on to SiNWs: an increase of surface areas in the porous profile and quantum confinement ascribed to the shrinkage of silicon skeletons. Since the first report on producing mpSiNWs in 2009, the emerging porous nanostructures are increasingly catching fundamental and technical interests, and diverse but limited applications have been explored in batteries, energy storage, photocatalysis, drug delivery and gas sensors. In this mini review, we will elaborate the porosification mechanism in metal-assisted chemical etching of Si wafers that has been dominantly employed to fabricate mpSiWNs, in terms of intrinsic properties of Si wafers (i.e. the doping level and dopant elements), ingredients of the etching solution, temperature and complementary porosification methods. Among various physical properties of mpSiWNs, photoluminescence (PL) has been intensively studied owing to the promising application of mpSiNWs in optoelectronics. PL of mpSiNWs sensitively varies with the intrinsic properties of parent Si wafers, temperature and porosification processes, and the origin is still ambiguous and under debate. It will be reviewed the current studies in PL, together with the antireflection that is highly desired in producing green energy. At the end, it will be envisaged the prospects of mpSiNWs for developing the integrated optoelectronic devices.