Highly sensitive determination of N+ doping level in 3C–SiC and GaN epilayers by Fourier transform infrared spectroscopy

In this study we determine by means of Fourier transform infrared spectroscopy the doping level of n-type doped 3C–SiC and GaN epilayers grown, respectively, on silicon and sapphire substrates. We show that a doping level can be established for both cases with a high accuracy by identifying relevant spectral features and by performing a simple analytical simulation. We discuss in what extent the spectral features which are used to determine the doping level can be attributed to the LO phonon–plasmon modes (LPP modes) for both cases. The influence of the substrate is also discussed. Complementary measurements performed by secondary ion mass spectroscopy (SIMS) attest the reliability of the method.