Reflectivity-based technique for the determination of the dielectric properties of materials : application to silicon carbide -

Abstract

Silicon Carbide (SiC) is a group IV semiconductor material that can function under extreme conditions such as high-operating temperature, high power, high switching frequency and high breakdown voltage. The wide band gap of SiC (2.2-3.3 eV) is useful for realizing short wavelength blue and ultraviolet optoelectronic devices such as light-emitting diodes. For this reason, there is much interest in studying the optical properties of the SiC near its band gap edge. Many authors investigated the dielectric functions of the most common SiC polytypes (3C, 4H- and 6H-SiC) using spectroscopic ellipsometry for experimental studies and first-principles calculations in theoretical works. However, these latter techniques suffer from the drawback of having too many fitting parameters and the assumption of a defect free pure crystal, respectively. In this work, we are proposing a new technique to determine, without the use of any fitting parameters, the dielectric properties of 4H- and 6H-SiC around the band gap. We start by measuring the reflectivity spectra of 4H- and 6H-SiC, using the UV-VIS spectrophotometer, for angles of incidence, theta, ranging from 10 to 60 degrees, using p and s polarized light. The experimental reflectivity values are used to obtain the frequency-dependent dielectric constant, epsilon, using the Kramers-Kronig equations, from which we extract the isotropic epsilon parallel, the index of refraction n and the extinction coefficient k. We found that our real (imaginary) values for the dielectric constant, epsilon, are lower (higher) than those reported in the literature. This is explained by the fact that our technique takes into account the presence of defects in the lattice, which enhance the absorbance of the material. This work contributes to the understanding of the relation between the silicon carbide polymorphism and the optical properties of a realistic defect containing SiC lattice.