The bidirectional reflectance distribution function (BRDF) describes spatial distribution of light scattered from rough surfaces and can be used to calculate other radiative properties. There have been many researches focus on the BRDF of rough surface structures. A number of approximate techniques such as perturbation theory, the Kirchhoff approximation, and geometric optics approximation (GOA) are widely used due to the complexity of the electromagnetic theory. However, these approximate techniques neglect some phenomenon such as surface plasmon polaritons (SPP), the diffraction effect, cavity resonance etc., which can be efficiently studied by the finite-difference time-domain (FDTD) method. As the increasing improvement of the computational science, it is feasible to simulate the radiative properties of complex surface structures by electromagnetic theory. Silicon tends to oxidize naturally, which hence changes the radiative properties of the rough surface structure. The focus of this study is on the effect of oxide films on BRDF of two-dimensional randomly rough surface of silicon using the FDTD method. The BRDF of different surface roughness of silicon substrate coated with oxide film has been investigated. The results show that, the BRDF of the rough surface of silicon will be affected by the RMS roughness (σ) and correlation length (τ). The energy of the reflection peaks increase as the roughness decreases (σ), when the correlation length (τ) remains the same. And the energy of the reflection peaks decrease as the correlation length decreases, when the roughness remains the same. The calculation domain and time increase as the rate of στ/λ increases. Moreover, when the rough surface of silicon covered with oxide film, the reflection peak will be weakened obviously, which is mainly due to that the absorbing oxide film.

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