Structural investigation of silicon carbide with micro-Raman spectroscopy

Silicon carbide (SiC) is a suitable wide band gap semiconductor for high power and frequency electronic devices. The most important advantages of the material are good thermal conductivity and high breakdown voltage. Surface oxidation of SiC wafers results in forming of native SiO₂ layer on the surface of the substrate. However, the material has significant drawbacks. The most important one for the application in electronic devices is the reduction of the carrier mobility by near interface traps (NIT´s) [1]. The origin of the traps that are formed near the SiC / SiO₂ interface is not clear. The possible defects which can play an important role in forming the traps are: defects formed in the vicinity of the SiC / SiO₂ interface [1]; Si₄C_4-xO₂ (x les 2) structures [2, 3]; carbon structures (mainly graphitic [3, 4] or dimers [5]) placed at the interface SiC / SiO₂; the structure of SiC layers placed in the vicinity of interface [2]; intrinsic oxide defects creating electronic states at 2.8eV below the oxide conduction band [6]. Raman spectroscopy is the experimental technique that can give information about the structure of the material without destruction of the sample. The Raman spectra depend on the investigated polytype [7] the size of the microcrystals and the ldquoimpuritiesrdquo such as carbon structures in the sample [4, 8, 9]. The aim of this work was to investigate different polytypes of SiC (4H and 3C) with one-phonon [7] and two-phonon [10, 11] Raman spectra. The attention was focused on this part of the range of the Raman Shift which contains the information about carbon related species that may be responsible for forming the traps. The structural data obtained from Raman spectra can be correlated with the electrical properties of the investigated structures.