Photodetective characteristics of Al/LPD-oxide/n-type Si MOS with tunnelling structures

The aluminum/oxide/n-type Si MOS tunnelling structure is utilised as a photodetector. The silicon dioxide (SiO₂) insulator was grown by a low temperature (30-40-C) and reliable method of liquid-phase deposition (LPD). The LPD process uses a supersaturated acid aqueous solution of hydrofluosilicic (H₂SiF₆) as a source liquid and an aqueous solution of boric acid (H₃BO₃) as a deposition rate controller. In this Letter, the LPD SiO₂ was prepared at 40°C with concentrations of H₂SiF₆ and H₃BO₃ at 0.4 and 0.01 M, respectively. Field-emission scanning electron microscopy shows the LPD SiO₂ with grain size ranging 40-50-nm. The element analysis of LPD-SiO₂, deposited onto n-type Si, is investigated by using Fourier transform infrared spectroscopy. The on/off ratio calculated from the dark and photo current densities rapidly changes at the threshold optical-power density. Defect-assisted tunnelling was invoked to explain these results. The authors suggest that a suitable LPD technology for the fabrication of the MOS tunnelling diode can be achieved.