Fabrication of LaF3 passivated porous silicon pH sensor by deep eutectic solvent based novel chemical route

Lanthanum fluoride (LaF₃) and other rare-earth halides are commonly used in sensor and optical equipment. A deep eutectic solvent (DES) based LaF₃ passivated porous silicon (PS) sensor for sensing the pH of buffer solution has been fabricated in this research. An electrochemically etched PS structure has been prepared and passivated with novel DES-based LaF₃ to fabricate pH sensor. For the deposition of LaF₃ thin film to create heterostructure devices, a variety of complex and costly processes have been employed. In a quest to find a facile technique to fabricate a pH sensor, this research presents the justification of sensing characteristics of DES-based spin-deposited LaF₃/PS structure. Energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) analyses both supported the almost stoichiometric and highly crystalline nature of LaF₃. Scanning electron microscopy (SEM) was used to confirm the uniform morphological structure. The sensing characteristics of fabricated pH sensors have been confirmed by studying the capacitance-voltage (CV) characteristics of prepared structure in a different buffer solution with different pH values. From the experimental results, it was observed that DES-based LaF₃ passivated PS structure shows voltage shift at the inflexion point of CV characteristics for different pH solutions. In light of this, it can be said that a pH sensor for sensing the pH levels of any buffer solution may be fabricated by depositing novel DES-based LaF₃ both inside the pores of PS and on top of it using the spin coating approach.