Impact of modified spin coating variations on electrical resistivity and UV detector responsivity in Mg-doped ZnO thin films

Abstract

This study addresses the impact of different spin coating speeds on the optical, structural, and electrical properties of the Mg doped ZnO films for UV detectors. XRD demonstrated that as the spin rate increased from 1000 to 3000 rpm, the film's crystallinity decreased from 35.66 to 15.74 nm. Increasing the rotation speeds from 2500 to 3000 rpm caused a shift towards lower 2θ values in the peak (101) of Mg doped ZnO thin films due to lattice contraction. SEM analysis reveals that spin coating speed results in a smoother surface, featuring a wrinkle pattern (2500 and 3000 rpm). The thickness of the thin films decreases significantly, from 608 nm to 240 nm. AFM measurements indicated a decrease in surface roughness from 78.12 nm to 18.9 nm. The optical properties of the higher spin coating speed show 96% transmittance. UV–Vis spectroscopy shows the absorption edge in the range 330–340 nm. The energy bandgap value increased from 3.13 eV to 3.37 eV. The vibrational peaks at 435 cm⁻¹ and 350 cm⁻¹ in the Raman spectra confirm the wurtzite structure of ZnO and the multi-phonon process. The examination of electrical properties via I–V characteristic curves reveals an ohmic behavior. The carrier concentration increased from 0.96 × 10¹⁴ cm⁻³ to 5.66 × 10¹⁴ cm⁻³, and the resistivity values decreased from 9.45 × 10³ Ω cm to 1.10 × 10³ Ω cm in Mg doped ZnO films. At 3000 rpm, the responsivity reaches 10.2 mA/W. This shows faster spin coating rates lead to higher responsivities, leading to better performance of the UV detector.