Surface modification of a-Si0.60C0.40:H films by Al-assisted photochemical etching: humidity sensing application

The paper investigates the formation of thin porous amorphous silicon carbide (PASiC) by Al-assisted photochemical etching using HF/AgNO₃ solution under UV illumination at λ = 254 nm. Different etching times varying from 2 to 10 min have been used on thin a-Si_0.60C_0.40:H films, which are elaborated by co-sputtering DC magnetron using a single crystal Si target and who deposited onto 86 of hot pressed polycrystalline 6H-SiC stripes of 12.5 mm³. Because of the high electrical resistivity of the thin a-Si_0.60C_0.40:H film higher than 2 MΩ cm, and in order to facilitate the chemical etching, a thin metallic film of high purity aluminum (Al) has been deposited under vacuum, follow-up of a thin palladium deposited under a grid to reduce attacked surface and reinforced solution etching. The etched surface was characterized by scanning electron microscopy, infrared spectroscopy, spectrophotometer UV, and photoluminescence. Results show that the morphology of etched a-Si_0.60C_0.40:H surface evaluates with etching time and presents a spongy and macroporous layers. Where, the diameter of pore size increases with the increasing etching time. A humidity sensors were fabricated through evaporating coplanar interdigital gold electrodes on PASiC and the humidity sensing properties were tested, it show, that the measured resistance Au-PASiC structure, depends highly on the applied bias voltage. Finally, the sensing performances are attributed to the unique surface structure, morphology of the pore and its size, that provide an effective pathway for vapor transportation and enlarged the sensing area of Au-PASiC.