Basic Theories of Semiconductor Electrochemistry - Electrochemistry of Silicon and Its Oxide - page 35

increases steeply when the depletion layer starts to form and a saturation current
is quickly reached. On the other hand, with sufficient surface recombination or in
cases of slow electron transfer reactions, the apparent onset of the photocurrent
can be shifted to higher bias and the saturation current is only reached at a larger band
bending.

1.5.2. Photopotential
Photopotential or photovoltage is the potential change in the space charge layer
resulting from charge separation of photogenerated excess carriers in the field of the
space charge layer under galvanostatic conditions. 86,962 It depends on the light intensity
and the original band bending in the dark. The maximum photopotential is obtained
when the energy band becomes flat. Also, depending on whether it is in depletion or
accumulation at the semiconductor surface, the photopotential can be negative or pos-
itive with changing sign at the flatband potential. 278 The photopotential developed in a
depletion layer is much larger than that in an accumulation layer.
When an electrode is illuminated its potential becomes

This change of potential by illumination, is defined as photopotential,
The current measured at is the sum of electron and hole currents:
At the open-circuit potential condition the net current is zero, that is, and the
photopotential is called the open-circuit photopotential, When there is very little
surface recombination and the electrode reaction is sufficiently fast so that the con-
centration of the reagents at the surface remains equal to their equilibrium values, the
relation between open-circuit photopotential and light intensity for an n -type material
407 by

can be expressed for