Raman characterization of local electrical properties and growth process in modulation-doped 6H-SiC crystals

Raman microspectroscopy has been applied to the determination of free carrier distributions in modulation-doped 6H-SiC crystals in order to examine the process of the crystal growth. The spatial distribution of the carrier concentration and mobility is extracted from the line shape analysis of LO phonon plasmon coupled modes using a dielectric function which takes into account the LO-phonon damping. The residual time of dopants in a growth furnace after the shut-off of the doping gas is inferred from the carrier density profiles. The growth rate of the crystals and incorporation of the dopants are also studied. The relationship between the carrier mobility and carrier concentration is determined from these quantities at different positions in the sample. It is found that the LO-phonon damping has much influence on the carrier damping and changes linearly with the carrier concentration in a range below ∼2×1018 cm−3.