Ammonia Gas Sensing Properties of GeO2:SnO2/Si Thin Films Prepared via Pulsed Laser Deposition
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Abstract
This study investigates the structural, optical and gas sensing properties of tin oxide (SnO₂)-doped germanium oxide (GeO₂) thin films synthesised by pulsed laser deposition (PLD) on Si (111) substrates. Doping concentrations of 2 wt %, 3 wt%, 5 wt% and 8 wt% were employed using a constant laser energy of 350 mJ. The fabricated films were evaluated for ammonia (NH₃) gas sensing at operating temperatures of 200°C, 250°C and 300°C. X-ray diffraction (XRD) analysis confirmed that the deposited films were polycrystalline in nature. The dominant crystalline phases were identified as hexagonal GeO₂ (101) and SnO₂ (110). Scanning electron microscopy (SEM) images revealed a progressive increase in particle size with increasing SnO₂ doping concentration. In contrast, atomic force microscopy (AFM) analysis showed an increase in grain size distribution, surface roughness and root mean square (RMS) values as the SnO₂ content increased. Optical measurements indicated that absorbance increased with higher SnO₂ doping levels, accompanied by a reduction in the optical band gap energy. Gas sensing measurements demonstrated that the GeO₂ film doped with 8 wt% SnO₂ exhibited the best performance, achieving a maximum sensitivity of 16% at 300°C under exposure to 100 ppm NH₃. The optimised sensor also showed fast dynamic behaviour, with a response time (t_res) of 26.1 s and a recovery time (t_rec) of 34.1 s. The remaining GeO₂:SnO₂/Si samples exhibited comparatively lower and varied sensing responses.
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References
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