the time that the excess carriers are available for the conduction process this can be accomplished by introducing impurity or native defects that act as minority carrier traps in the semiconductor material fig2 schematically shows the conduction and valence band of a photoconductive material having minority carrier traps immediately after the electron hole pair is created an electron from the defect center traps the excess hole in other words the hole is raised to the defect level since the hole is now localized at the trap level there is a low probability that the excess electron will recombine with the hole until the hole is re emitted from the trap to the valence band the time required for the hole to be re emitted increases the time that the excess electron is available in the conduction process thus increasing the photosignal by increasing the photoconductive gain under the proper conditions this increase in time and signal can be many orders of magnitude generally the lower the temperature of operation at the quiescent state the greater the magnification of gain fig3 represents the movement of an electron hole to the trap level upon incidence of a signal photon flux q s thus for effective operation of a photoconductive.