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Nano-silicon dioxide (SiO2) has been deposited on an n-type silicon substrate using the spin-coating method and Al/nano-SiO2/n-Si MOS photodetectors have been fabricated to characterise their optical properties using current-voltage (I-V) measurements. Field emission scanning electron microscope (FESEM) shows the spin oxide with grain size ranging from 25 to 30 nm, demonstrating the sol gel method to be homogeneous in grain size. The ratio of photo to dark current was 25.3 and 9.1 for the wavelength of 632 and 850 nm, respectively, for the MOS detector under negative gate with six voltages. The quantum efficiency was obtained as 76.1 and 74.8 for the wavelength 632 and 850 nm, respectively. These results suggest that a suitable spin-coating technology for the fabrication of the MOS tunnelling diode can be achieved.