Selective Photosensitivity of Metal–oxide–semiconductor Structures with SiOx Layer Annealed at High Temperature

SiOx layers with x = 1.15 and 1.3 and thicknesses of 50 and 100 nm were deposited on crystalline silicon wafers by thermal evaporation in vacuum. Part of the samples were annealed at 250 °C (control samples), while the rest were annealed at temperatures of 700, 800, and 1000 °C. The high-temperature annealing leads to phase separation and formation of Si nanoclusters in a dielectric matrix with higher x than the initial one. Metal–Oxide–Semiconductor structures were fabricated and characterized by current–voltage and capacitance–voltage measurements. The relative permittivity (εr) and refractive index (n) of the layers depend on the annealing temperature and vary in the 5.4–6.9 (εr) and 1.72–1.90 (n) ranges for x = 1.15. For x = 1.3, εr and n vary in the 5.1–6.5 and 1.67–1.78 ranges, respectively. All annealed samples showed selective photosensitivity as the responsivity increases with the photon energy. The observed effect is explained by assuming that the blue and UV lights provide sufficient energy to photocarriers generated in the Si wafer to be injected into the SiOx layer at relatively low electric fields, ~ 0.3 MV/cm for layers annealed at 700 and 800 °C and ~ 1 MV/cm for those annealed at 1000 °C (x = 1.15). It was found that the current through the annealed layers under UV and blue light illumination is controlled by Fowler–Nordheim tunneling. The structures with x = 1.3 show higher selectivity to UV light but lower responsivity compared to structures with x = 1.15. No selective photosensitivity was observed in the control samples.