Photoconductive switch

A photoconductive switch comprises a first layer (1), two contact layers (2, 3) arranged on said first layer and connectable to different potentials for applying a voltage thereacross, said first layer being adapted to be conducting upon applying a voltage across said contact layers when exposed to light from an illumination source of an energy high enough for lifting charge carriers from the valence band to the conduction band of the material of said first layer. The illumination source is an excimer lamp, in which unstable electronically excited dimers are formed when a voltage is applied across first and second electrodes (12, 13) separated by a gas or gas mixture. The dimers so formed decompose into two gas atoms while emitting a photon of an energy suitable for lifting charge carriers from the valence band to the conduction band of the material of the first layer.