Anodic Behavior - Electrochemistry of Silicon and Its Oxide - page 169

silicon At potentials more positive than that of it is characterized by the
formation and dissolution of a surface oxide film resulting in a smooth surface, referred
to as electropolishing. 33 The current in this region indicates the growth and dissolution
rates of the oxide film. Also, the current at potentials more positive than that of
is not constant, indicating that the oxide formed at different potentials has different
properties. The values of the characteristic currents, to which may occur at
different potentials for p -Si and n -Si, are a function of electrolyte composition but
are largely independent of doping, since they are determined by the properties of the
anodic oxide. At potentials more positive than the second plateau current, current
oscillation may occur. Also, oxidation of water becomes an important reaction at these
positive potentials in addition to the oxidation reaction of the silicon electrode. The
surface resulting from dissolution at potentials higher than the second peak is brightly
smooth, while that produced between the first and second peak is relatively less
smooth. 38

The anodic behavior is the same for p- and n -type materials when the rate
of carrier transfer between the surface and the semiconductor bulk is sufficiently
2,69,700,763 The i-V curves of the two materials, when the current is not limited by
the supply from holes in the semiconductor, are largely identical except for a shift
along the potential axis for materials of different doping levels. For n -Si, large cur-
rents can be achieved by either sufficient illumination intensity or degenerate doping.
Thus, the reaction processes, which are the same for all types of silicon, are determined
by the chemical nature of silicon material and the electrolyte independent of the
electronic nature of silicon. Different doping conditions affect the rate of charge
transfer between the surface and the semiconductor but not the chemical nature of the
reactions.
Figure 5.3, as a detailed i-V curve around the first peak, shows that the current
increases exponentially with increasing potential from OCP. 2 It breaks off from the
exponential dependence on potential at large overpotentials, exhibits a peak,

fast.

and

then attains a relatively constant value at Examination of the surface of the samples,