Proceeding in order from the light-side to the beam-side of the target structure, the structure includes a transparent glass plate, a transparent signal electrode, a photoconductive layer of n-type CdSe, and a layer of n-type ZnSe. The interface between the two n-type layers is possessed of a multitude of interface states capable of capturing holes optically liberated in the photoconductor and electrons injected by the scanning beam. Beam-injected electrons cannot pass directly across the interface, and therefore dark current is reduced in a manner as effective as with p-n junction target structures. Each optically generated hole trapped at the interface lowers the potential barrier for beam-injected trapped electrons by an amount such as to cause more than one such electron to enter the conduction band of the CdSe layer, resulting in greater-than-unity amplification. Amplification by factors in excess of 100 can be achieved.