an electron beam controlled semiconductor switch is capable of carrying large currents without being restricted by the space charge limited current condition . the switch includes a block of semiconductor material having ohmic contacts connectable to first and second electrical conductors . semi - insulating gaas may be used as the semiconductor material . a shallow donor or acceptor doped layer may be formed at the surface receiving the electron beam for increased band - edge radiation . this recombination radiation ionizes , together with x - rays produced by bremsstrahlung , the bulk of the semiconductor block to provide relatively high current density and current gain .