Defect levels in Cu(In1-x,Ga-x)Se-2 (CIGS) were studied by using admittance spectroscopy with varying Ga concentration of x from 0.38 to 1.0. Two distinct peaks (alpha and zeta) were detected from all of CIGS samples. Peak alpha. could be attributed to the shallow acceptors. Peak zeta was closely correlated with the surface potential of CIGS; therefore, it may have been caused by traps near the surface of CIGS such as grain boundary defects. The intensity of peak increases with increasing Ga concentration. Further, this intensity was correlated with the ideality factor of the A1/CIGS Schottky junction. We suggest that the degradation of the performance of CIGS solar cell with increasing Ga concentration may be concerned with defects corresponding to peak zeta. (C) 2006 Elsevier B.V. All rights reserved.