Enhancement of Performance Au/PSi/n-Si/Ag Heterojunction Photodetector by Non-thermal Plasma Jet: Design and Impact of Plasma Voltage

We have investigated the impact of non-thermal plasma jet (NTPJ) on porous silicon (Psi) nanostructures prepared by photoelectrochemical etching (PECE) and subsequently studied this effect on the performance of the PSi-based photodetectors, where the influence of a non-thermal plasma jet on a porous silicon surface has not been examined in any previous study. PSi samples were treated with 12, 14, and 16 kV voltages by a non-thermal plasma jet for a fixed fluence duration of 12 min. The X-ray diffraction (XRD) pattern reveals that the size of porous silicon crystallized increased from 28.6 nm to 75.0 nm when the plasma voltage was raised to 16 kV. Field emission scanning electron microscopes (FE-SEM) images revealed that the gray, mud-like, and dark porous sample turned into a tending black and more porous surface, and the treatment by plasma altered the top surface of the porous layer only without causing any damage to the sample. The study of atomic force microscopy (AFM) images showed that the surface roughness RMS, roughness average Sa, and the top ten highest roughness Sz of porous silicon increased from 1.50, 1.10, and 13.7 nm to 5.21, 3.69, and 64.59 nm, respectively, after treated at 16 kV plasma voltage. Raman scattering spectra of treated materials show visible photoluminescence and an infrared shift due to plasma treatment of porous silicon PSi, with a crystalline structure band at 548 cm⁻¹. The photoluminescence (PL) spectrum shows multiple peaks and shifts toward longer wavelengths after plasma treatment. The responsivity of Au/PSi/n-Si/Ag photodetectors increases with plasma voltage, reaching its highest values at 16 kV (9.28 and 10.83 W/A at 480 and 600 nm) and the maximum detectivity of 2.47 × 10¹² and 2.8 × 10¹² Jones at 480 and 600 nm. Photodetectors performance was evaluated based on repeatability and photo response speed. The stability of Au/PSi/n-Si/Ag, heterojunction photodetectors, was tested at -1 V bias voltage and 4 s switch cycle, demonstrating constant maximum current values.