Toward scalable manufacturing of doped silicon nanopillars for thermoelectrics via metal-assisted chemical etching

Abstract

Metal-Assisted Chemical Etching (MACE) using Ag as the catalyst lets prepare vertically aligned crystalline silicon nanopillars (SiNPs), a highly promising system for thermoelectric applications, with high aspect ratios in a wide doping range. MACE may be implemented either by using Ag both as the catalyst and the oxidant (so-called one-pot MACE) or by using another chemical (typically H₂O₂) as the oxidant (two-pot MACE). This study investigates how the localized etching rate depends upon Si doping in both MACE implementations, accounting for the concurrent non-catalyzed etching. The latter, which shortens SiNPs, is found to become more significant in p-type Si at higher doping levels due to the narrower space-charge regions at the bare Si-solution interface. We demonstrated that in both one- and two-pot MACE the etching rate is controlled by the band bending at silicon–silver interface. In p-type silicon, it decreases with doping due to faster hole diffusion, while the Schottky barrier at the interface hinders hole injection in n-type silicon at any doping level. Overall, we highlight that MACE may be effectively implemented in its one-pot version, facilitating MACE scale-up toward SiNP large-scale manufacturing.