Environmental Engineering Reference
In-Depth Information
Se
In
Cu
Figure 3.4
The atomic percentage of individual elements as determined
from XRF for material layers grown at different voltages using a two-
electrode system [16]. See also Colour Insert.
3.4.3
Observations in PEC Cell Measurements
Electrodeposited semiconducting layers are usually grown on
conducting surfaces like glass/conducting glass substrates. The
thickness of the electrodeposited layers can be in the sub-micron
range (50-1,000 A), and hence the determination of the electrical
conduction type using standard techniques like the Hall effect is a
challengingtask.AsolutiontothisisasimplePECcellmeasurement.
A system like glass/conducting glass/semiconducting layer can
be used to form a solid/liquid junction between the semiconductor
and a suitable electrolyte. This junction is very similar to a
Schottky diode formed at a semiconductor/metal interface. The
only difference is the replacement of the metal contact with a
conducting electrolyte. The open circuit voltage of this junction
can be determined easily by measuring its voltage with respect
to another electrode under dark and illuminated conditions. The
difference between the two readings — the open circuit voltage of
the solid/liquid junction — is the PEC signal, which can be used
to identify the electrical conduction type of the semiconductor. The
signofthePECsignaldeterminestheelectricalconductiontype,and
