Using 1150 nm infrared light, the change in the detector sensitivity w
as studied. As a simple measure of the states of the detector sensitiv
ity, the time derivative of the photocurrent is proposed. In terms of
the derivative, the change is uniquely classified into two categories.
Even after the detector is aged, the derivative does not remain const
ant with respect to time and voltage. The physical mechanisms which ca
use the change are discussed based on possible effects due to unstable
surface states and the accumulation of an oxide layer.