Microstructural and infrared optical properties of electrochemically etched highly doped 4H-SiC

Pores in porous 4H-SiC are found to propagate first nearly parallel with th e basal plane and then gradually change plane of propagation towards the di rection of the c axis. A similar anisotropy in pore propagation is found in porous 6H-SiC. A disordered phase is encountered at the interface between crystalline SiC and the pores. Formation of this phase was attributed to th e etching conditions. Characterization of the material with nondestructive infrared spectroscopic ellipsometry in the photon energy range 0.062-0.62 e V provides average thickness and porosity in good agreement with electron m icroscopy observations. Anodization of SiC introduces remarkable changes to the reststrahlen band. A shallow minimum at 0.113 eV is attributed to the Berreman effect. In addition, a sharp peak at 0.126 eV is discussed to be r elated to the in-depth inhomogeneity and particle shape effects in the mate rial. (C) 2000 American Institute of Physics. [S0021-8979(00)07312-6].