Photoluminescence of samples produced by electroless wet chemical etching: Between silicon nanowires and porous structures

Samples containing silicon nanowires (Si‐NWs) and highly porous structures (P‐Si) were prepared by electroless wet chemical etching (EWCE) of crystalline silicon wafers using various etching parameters. Photoluminescence (PL) measurements were performed with excitation at 488 nm and a photon energy flux of 337 mW cm−2. According to the diameters of the Si‐NWs (>10 nm), from quantum confinement (QC) theory no shift in PL peak energy compared to the bandgap of crystalline silicon is expected. However, PL measurements show peak emission energies ranging between 1.4 and 1.6 eV. After further treatment of the samples with HF, substantial PL emission was still detectable with the measured PL peak pinned at 1.4 eV irrespective of etching time. We explain the observations by the hypothesis that the persistent part of PL emission is generated by nanocrystals located at the rough sidewalls of the Si‐NWs or residing within the porous sample structure. The part of the PL, which was present before HF treatment, but vanished after the treatment, is attributed to the presence of silicon suboxide surrounding the Si‐NWs or covering other Si surfaces. This hypothesis is explored by means of three sample series, prepared with different preparation parameters. In the first series the time used during the initial metallization step in order to prepare an Ag nanoparticle layer on the top surface was varied, in the second series the etching time was the changed parameter and in the third series the HF to H2O2 concentration ratio was varied. Strong visible orange colored PL of a sample produced by EWCE starting from a heavily doped wafer (n‐type c‐Si (111), As as dopant) and excited at 337 nm (the sample was mounted on a glass substrate. Blue luminescence is due to the substrate).