Anodic Behavior - Electrochemistry of Silicon and Its Oxide - page 189

and Lubke, 11 reduction of generates holes equivalent to the photogenerated holes.
The holes so generated are consumed by the oxidation of silicon forming intermedi-
ates which are further oxidized by injecting electrons into the conduction band as shown
in Fig. 5.31. In this case the limiting current depends on the rate of

reduction

controlled by the mass transport of A similar effect is observed by adding to the

256,541,969

solutions other oxidants such as or

5.7. IMPEDANCE OF INTERFACE LAYERS

The impedance of an electrode/electrolyte interface is one of the characteristic
quantities that reveals the electrical nature of the interface. The electrical structure of
the interface layers and the resistance to charge storage and movement can be analyzed
by determining the impedance as a function of frequency. The characteristics of the
electrochemical impedance of the silicon/electrolyte interface are different for n -Si and
p -Si and depend on among other factors, electrolyte composition and particularly the
concentration of fluoride.
Figure 5.32 shows the impedance plots for on a lowly doped p (100) silicon
sample in 1% HF solution at potential values corresponding to those marked on the i-

V

curve in Fig. 5.33. 9,475 The impedance exhibits three characteristic capacitive loops.
At low potentials, close to OCP, a single loop is observed as shown in Fig. 5.32a at
This loop, loop I, may be seen at more positive potentials at high frequen-
cies as shown in Fig. 5.32b. The capacitance associated with this loop is estimated to
be about According to Searson and Zhang, 9 since a near-perfect Mott-
Schottky relation is also observed in this potential region, the single capacitive loop
occurring at ariseses from the space charge layer in the silicon.
A second capacitive loop, loop II, starts to be seen at potential values about
which is about 0.1 V more positive than that shown in Fig. 5.32a, and gains