Experimental results on the temperature dependence of the magnitude and pol
arity of surface photo-charge effect in CdS an presented for optical excita
tion in both the sub-bandgap and the intrinsic absorption spectral range. I
t is shown that such a dependence can provide information on thermally acti
vated changes in the occupancy of surface levels. (C) 1999 Elsevier Science
B.V. All rights reserved.