Passivation of Porous Silicon by LaF₃Using a Simple Single-Source Chemical Bath Technique

Passivation of porous silicon (PS) by LaF₃ by a novel chemical-bath technique has been investigated in this report. The porous silicon surface has been passivated with LaF₃ by reacting LaCl₃ with HF in the etching chamber at room temperature. Without removing the porous silicon from the anodizing chamber LaF₃ as a result of chemical reaction between LaCl₃ and HF was allowed to passivate the PS surface. Several cycles of reaction that gives the various thickness of LaF₃ layer on PS have been investigated. The Scanning Electron Microscopy (SEM) on the surface of LaF₃/PS/Si structure confirms the LaF₃ film deposition on PS layer. The X-ray diffraction (XRD) of the deposited layer revealed a hexagonal nanocrystalline LaF₃ deposition. The as-deposited thin (10-cycle) LaF₃ layer contained very low concentration of lanthanum (La) and fluorine (F). The concentration of La and F started increasing with the increase in reaction cycle. But the photoluminescence (PL) of as deposited-LaF₃ passivated PS was lower than that of fresh PS. Annealing the just passivated PS structure recovered the PL intensity. Experimental results show that the optimized chemical bath passivation process for the LaF₃ on porous silicon could enable the porous silicon to be an important material for photonic application.