Long-time Stability of the Enhanced Porous Silicon Opto-electrical Properties by Samarium Pore-filling

The long-time stability of the enhanced porous silicon (PS) optoelectronic properties using samarium (Sm) pore-filling were investigated based on experimental results. Non treated natural and thermally oxidized PS samples were taken as reference. The morphology evolution of the samples was observed by using a scanning electron microscope (SEM). Fourier-Transform Infrared spectra (FTIR) of Sm treated PS (Sm-PS) show the appearance of new band localized at 470 cm⁻¹ and attributed to Sm–O-Si which is persistent after 7 months of air exposure. Photoluminescence (PL) characterization demonstrated a stable threefold increase in the PL intensity of the Sm-PS. However, a blue shift from 1.829 eV to 1.835 eV and 1.890 eV for both natural aged and the thermal annealed PS samples accompanied with a dwindling in the intensity are observed and attributed to the decrease in the silicon crystallite size. The deconvolution of Raman spectrum of Sm-PS sample shows the existence of three bonds localized at 520, 518 and 506 cm⁻¹ and attributed to the crystalline Si substrate, the formation of silicon nanocrystallites (SiNCs) and the compressive strained PS layer after the deposition of Sm layer, respectively. The electrical properties were analyzed based on the effective minority carrier lifetime (τ_eff) and surface recombination velocity (S_eff). The Sm treated samples show the highest τ_eff about 52 µs and as a result the lowest S_eff comparing to the freshly prepared PS which exhibits a τ_eff of about 13.2 µs due to the passivating capability of Sm layer. These results highlight the effectiveness of coating PS with Sm layer suitable for light emission and photovoltaic applications.