Optical properties of one-dimensional porous silicon photonic crystals coated with a thin nickel film

Abstract

The surface of the one-dimensional porous silicon photonic crystal was modified by depositing a thin nickel layer with a nominal thickness of 80 nm. Optical characterization, performed via reflectance spectrum simulation and experimental measurements, demonstrated that the sequence of unit cells in the uppermost layers significantly affects the morphological characteristics of the porous structure. This effect leads to the formation of layers with inhomogeneities in thickness and porosity. After nickel deposition, fitting analysis employing the transfer matrix method revealed that photonic devices with low porosity and smaller pores in their first upper layer exhibit higher reflectance at the wavelength below the photonic band gap center, along with a narrower photonic band gap. This enhancement is attributed to the reflectance contribution of the relatively thin nickel film formed by the partial sealing of the small pores. In contrast, devices with greater porosity and larger pores exhibit suppressed photonic band gaps, making the photonic structure highly effective as an absorptive material. After thermal treatment, a partial recovery of the reflectance and the shape of the photonic band was observed. This recovery was more pronounced on the left edge, reaching approximately 80 % in the device with high porosity in their initial layer, while those with low porosity reach only around 40 % recovery.