Chemistry Reference
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where
V
is the applied potential,
the breakdown potential,
the photocurrent at
low voltage where no carrier multiplication takes place, and
n
a constant. The initial
excess voltage during anodization is expressed as
with
L
the light intensity and the minimum intensity which can supply a sufficient
number of holes required for anodic reaction without carrier multiplication in the deple-
tion region.
3.4.4. Electroluminescence
According to Hasengawa
et al
.,
370
the mechanism of the luminescence can be
described using the diagram shown in Fig. 3.18. The low ionic current efficiency during
anodization indicates that a considerable amount of electronic current flows through
the conduction band during anodization. Electrons are able to tunnel directly from the
energy states in the electrolyte into the conduction band of Some of these elec-
trons lose energy by emitting photons whose energy corresponds to the conduction band
discontinuity, about 3.1eV, and give rise to the HE peak. Some of the electrons lose
energy by falling into traps that are located about 2 eV below the conduction band of
which is responsible for the LE peak.
A different model for the illumination mechanism is provided by Zhou
et al
.
230
In this model, dielectric breakdown is considered to occur within the oxide because the
field strength in the
down voltage. Electron and hole pairs are generated at breakdown and the electrons are
accelerated under the field to become hot electrons. The scattering of these electrons,
layer during growth is 22 MV/cm which is around the break-
