Electron microscopy and spectroscopic ellipsometry are used to investigate
the microstructural and optical properties of porous SiC. It is discussed t
hat 1c dislocations are likely to play a role in the initial phases of the
anodization process in terms of formation of nanometer sized holes. Pores a
re found to initially propagate nearly parallel with the sample surface and
gradually change direction toward the c axis. Pore sizes are found to incr
ease with depth toward the interface between the porous SiC and the substra
te. A different pore morphology is found along the internal surfaces of mic
ropipes, where structures are relatively large in size and appear spherical
in shape. The anisotropy in pore propagation influences the etch rate, whi
ch varies in a nonlinear manner with the anodization time. The etching rate
is also influenced by the larger absorptivity of the porous layers caused
by formation of a disordered phase at the interface between the crystalline
SiC and the pores. Ellipsometric analysis of porous SiC layers yields thic
knesses and porosities in good agreement with the electron microscopy obser
vations. Optical properties of the solid content of the porous layers are s
ignificantly different from those of bulk crystalline SiC, and depend on th
e etching time and sample thickness. (C) 2001 The Electrochemical Society.