Structural, compositional and electrical characterization of Si-rich SiOx layers suitable for application in light sensors

Metal-Oxide-Silicon (MOS) structures containing silicon nanoparticles (SiNPs) in three different gate dielectrics, single SiOx layer (c-Si/SiNPs-SiOx), two-region (c-Si/thermal SiOx/SiNPs-SiOx) or three-region (c-Si/thermal SiO2/SiNPs-SiOx/SiO2) oxides, were prepared on n-type (100) c-Si wafers. The silicon nanoparticles were grown by a high temperature furnace annealing of sub-stoichiometric SiOx films (x=1.15) prepared by thermal vacuum evaporation technique. Annealing in N2 at 700 or 1000 °C leads to formation of amorphous or crystalline SiNPs in a SiOx amorphous matrix with x=1.8 or 2.0, respectively. The three-region gate dielectric (thermal SiO2/SiNPs-SiO2/SiO2) was prepared by a two-step annealing of c-Si/thermal SiO2/SiOx structures at 1000 °C . The first annealing step was carried out in an oxidizing atmosphere while the second one was performed in N2. Cross-sectional Transmission Electron Microscopy and X-ray Photoelectron Spectroscopy have proven both the nanoparticle growth and the formation of a three region gate dielectric. Annealed MOS structures with semitransparent aluminum top electrodes were characterized electrically by current/capacitance–voltage measurements in dark and under light illumination. A strong variation of the current at negative gate voltages on the light intensity has been observed in the control and annealed at 700 °C c-Si/SiNPs-SiOx/Al structures. The obtained results indicate that MOS structures with SiO1.15 gate dielectric have potential for application in light sensors in the NIR–Visible Light–UV range.