Influence of synthesis time on the performance of ZnO NPs/nSi heterojunction photodetectors prepared by non-thermal jet plasma

In this study, zinc oxide nanoparticles (ZnO NPs)-based photodetectors were fabricated using non-thermal argon jet plasma (NTP) at different synthesis times (8, 12, and 16 min). The nanoparticles were deposited on glass and silicon substrates by drop-casting at 40 °C. The non-thermal atmospheric jet plasma (NTAPJ) was operated at an applied voltage of 14 kV and a gas flow rate of 3 L/min, and the plasma parameters were calculated to confirm its stability and efficiency in producing nanoparticles. The effect of ZnO NPs synthesis time on the structural, topographical, morphological, and optical properties of ZnO NPs films deposited on glass substrates and of ZnO NPs/Si composites was systematically studied using X-ray diffraction (XRD), energy-dispersive X-ray analysis (EDX), atomic force microscopy (AFM), field emission scanning electron microscopy (FE-SEM), UV–Vis spectroscopy, and photoluminescence (PL) spectroscopy techniques. As the synthesis time increases, FE-SEM images reveal a notable change in the morphology of ZnO nanoparticles and nanowalls, including grain distribution, higher density, and increased thickness, indicating regular development and crystallization, which demonstrates a better structure. The optical properties of ZnO nanoparticle thin films show strong absorption below 400 nm. The optical energy band gap (\({\text{E}}_{{\text{g}}}\)) was calculated to be 3.8, 3.7, and 3.6 eV, indicating reduced crystalline size and increased thickness. Raman spectra showed peaks at 204–190 cm⁻¹ (E1 (LO)), 406 cm⁻¹ (E₁ (TO)), and 565 cm⁻¹ (A₁ (LO)), with increased intensity at 16 min, indicating improved crystallinity. EDX revealed an increase in Zn content from 6.5% to 17.8%. XRD revealed peaks at (100), (002), and (101), confirming the wurtzite structure with a decreasing crystalline size, which reflects a quantum confinement effect and improved crystallinity. The duration of synthesis by jet plasma was observed to affect the ZnONP's topographical roughness parameters. This study explores the impact of non-thermal plasma synthesis time on the physical properties and performance of nanostructured zinc oxide photodetectors in the UV–Vis region. This study highlights the impact of synthesis time on the ZnONPs/Si photodetector's figure of merit characteristics. It was found that the device performed best at a synthesis time of 16 min, with a responsivity of 24.8 A/W, EQE of 54%, and detectivity of 153.1 × 10¹¹ Jones at -5 V bias voltage. In addition, it demonstrated stable and unchanged properties with rise and recovery times of 0.25 s and 0.27 s, respectively. These findings can have a significant role in promoting the ZnONPs/Si photodetector responsivity.

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