A theoretical model gibing a time-independent description of a photorefract
ive surface-relief grating in a cubic crystal placed in an external constan
t electric field is proposed. The model is used to calculate the height of
the surface barrier of a Bi12TiO20 crystal for the (001) cut, where there i
s no interaction of light beams in the interior volume of the medium. (C) 1
999 American Institute of Physics. [S1063- 7850(99)01309-9].