Chemical Excitation of Silicon Photoconductors by Metal-Assisted Chemical Etching

The chemical transformations taking place during many of the reactions of the Si surface have been well documented, but the in situ dynamics of the reactions remain largely unexplored even for widely used electrochemical processes such as metal-assisted chemical etching (MACE). In this work, we design both n-and p-type Si photoconductors covered with silver nanoparticles to demonstrate photo-conductors' sensitivity to the MACE process and their ability to provide in situ information about the dynamics of the reactions occurring during MACE. The experimental results show that both n-and p-type photoconductors exhibit a response to MACE that is much stronger than their response to light with an intensity of 2 mW/cm2. The observations are further explained by a thermodynamic analysis of the relevant energy levels of the system, showing how both electron and hole injection into the conduction and valence bands by the Si/etching solution interface contribute to the photoconductors' response and excite Si. These results clearly demonstrate a new chemical operating mode for photoconductors, showing that in addition to being sensitive to excitation by light, a photoconductor can also be excited by chemical reactions providing means to monitor the dynamics of the reactions in situ and thus also for chemical sensing.