Structural and electrical properties of PSi/CNT junction

Electrochemical etching was performed in a highly acid-resistant Teflon electrochemical cell. A current density of 15 mA/cm² was applied using the silicon samples as the cathode. These samples were fixed and immersed in an etching solution composed of 18 % hydrofluoric acid mixed with ethanol. The ethanol facilitated the removal of hydrogen bubbles generated during etching, enabling the formation of regular and uniform pores. Carbon films with thicknesses of 20 nm and 50 nm were deposited onto the porous silicon (PSi) surface via plasma spraying from carbon rods. Raman spectroscopy of the 20 nm carbon-porous silicon junction revealed peaks corresponding to carbon nanotubes at 170, 1402, and 1533 cm^-1, while peaks associated with porous silicon appeared at 554, 977, 1154, 2940, and 3363 cm^-1. For the 50 nm carbon film, the Raman spectrum of the PSi/CNT junction exhibited carbon nanotube peaks at 190, 1407, and 1540 cm^-1, and silicon peaks at 564, 1000, 1144, 2945, and 3366 cm^-1. X-ray diffraction spectra of the PSi/CNT junction showed sharp peaks at 28.62° and 28.15° for carbon nanotubes in the 20 nm and 50 nm films, respectively. Electrical characterization demonstrated that PSi-CNT junctions exhibited lower current flow under dark conditions compared to Si-CNT junctions. However, increasing the carbon layer thickness enhanced the electrical conductivity of the junctions under both dark and illuminated conditions. This improvement is attributed to the greater amount of carbon anchored on the porous silicon matrix as the thickness of the deposited carbon layer increases.