ABSTRACT
In this work, p-type (100) and n-type (100) silicon wafers were used to synthesize porous silicon PS1 and PS2 via electrochemical etching. Silver nanoparticles (Ag-NPs) were synthesized by the laser ablation technique and uniformly deposited to the porous substrates using the spray pyrolysis. Field emission scanning electron microscopy (FESEM) revealed that the average pore sizes of PS1 and PS2 were 12.41 nm and 16.67 nm, respectively. X-ray diffraction (XRD) at 2θ = 69.34° confirmed the formation of PS1 and PS2 layers. Fourier-transform infrared spectroscopy (FTIR) showed Si-H₂ and Si-O-Si vibrational bands at 904, 1045 cm⁻¹ for PS1 and 904, 1035 cm⁻¹ for PS2.
Ultraviolet-visible (UV-Vis) spectroscopy confirmed the synthesis of Ag-NPs, exhibiting an intense peak near 400 nm. FESEM revealed that the Ag-NPs had an average diameter of 15.95 nm (16.74 nm by XRD). Zeta potential of -35 mV and electrophoretic mobility of -2.5 × 10⁻⁴ cm²/V·s for Ag-NPs, indicated a strong electrostatic repulsion, good colloidal stability, and the presence of surface hydroxyl groups, as confirmed by FTIR, which showed characteristic O-H stretching vibrations at 3255 and 3346 cm⁻¹.
Energy dispersive X-ray spectroscopy (EDS) indicated Ag contents of 1.88% (PS1– Ag-NPs) and 2.03% (PS2– Ag-NPs). According to Photoluminescence (PL) test, when PS1 excited with 375 nm light, it emitted red light at 747.143 nm (bandgap 1.66 eV), and after adding Ag-NPs, it shifted to blue light at 461.83 nm (bandgap 2.68 eV), while PS2 emitted at 731.12 nm (bandgap 1.70 eV), showing it has tiny crystal areas، after adding Ag-NPs, it shifted to blue light at 454.43 nm (bandgap 2.73 eV), indicating better quantum confinement and light emission.
The performance of PS and PS- Ag-NPs-based photodetectors (PDs) was tested under white-light illumination at voltages from -5.2 V to +5.2 V and intensities of 1, 1.5, 2, 4, 8, 16, 20, 30, 45 and 60 mW·cm⁻². Sensitivity (S) and responsivity (R) were measured at ±3.2, ±4, and ±5.2 V. At -3.2 V, the PS₁- Ag-NPs PD showed S increasing from 790.8% to 1516%, and at +5.2 V, R rose from 0.207 to 0.85 A·W⁻¹ compared with the PS₁ PD. For PS₂- Ag-NPs PD, S increased from 1784% to 5568% at +3.2 V, while R improved from 0.556 to 2.94 A·W⁻¹ at -5.2 V, indicating pronounced enhancement over the PS₂ PD.
I-T measurements showed PS₂- Ag-NPs PD at +5.2 V and 60 mW·cm⁻² had faster response (82 µs) and recovery (473 µs) than PS₁- Ag-NPs PD (112 µs, 645 µs) due to larger pores and smaller, uniformly distributed Ag-NPs. Also, At 1 mW·cm⁻², PS₂- Ag-NPs PD recorded 295 µs/101 µs, while PS₁- Ag-NPs PD had 378 µs/124 µs.
The spectral photoresponse of PS₁, PS₂, PS₁- Ag-NPs, and PS₂- Ag-NPs PDs was measured under 3.2, 4, and 5.2 V bias and irradiance from red (1.4 mW·cm⁻²) to UV (2.2 mW·cm⁻²). Ag-NP integration enhanced photocurrent via localized surface plasmon resonance and enhanced carrier transport. PS₂- Ag-NPs PD achieved the highest response (70 µA), particularly in the UV-green range (395-550 nm) due to optimal pore-NP size matching, while PS₁- Ag-NPs PD showed moderate gain at ~540-580 nm. Red (>600 nm) remained weak, whereas UV-blue (<480 nm) showed marked improvement in Ag-NP-modified devices. Overall, PS₂ -Ag-NPs PD demonstrated the greatest enhancement, underscoring their strong potential for high-performance optoelectronic applications.
