Efficient passivation of porous silicon with LaF3 by deep eutectic solvent based novel chemical route

Abstract

Sensors and optoelectronic devices frequently employ rare-earth halides like lanthanum fluoride (LaF3). This article presents the investigation on the passivation of pore walls of porous silicon (PS) with LaF3 using a deep eutectic solvent (DES) based novel chemical route. The DES, called ethaline, a 1:2 M solution of choline chloride and ethylene glycol, has been used as the solvent of LaF3. Spin-coating deposits the precursor solution on the pore wall of PS, and subsequent annealing evaporates the DES leaving LaF3 on the pore wall as a passivating layer. Energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) analyses indicated an almost stoichiometric and highly crystalline nature of deposited LaF3. The surface of the LaF3 was uniform and crack-free as revealed by scanning electron microscopy (SEM). The photoluminescence (PL) behavior of the LaF3-passivated PS structures further supported the passivation of PS. Compared to the freshly prepared PS without LaF3 passivation LaF3-passivated PS structure exhibits stable photoluminescence. The investigations show that the facile DES-based chemical route with the simple spin-coating technique can provide good passivation of PS by the LaF3 layer that may enable LaF3-passivated PS to be an ideal candidate for low-cost electronic and optoelectronic devices.