Metal–insulator–semiconductor emitter with an epitaxial CaF2 layer as the insulator

An 8-nm-thick epitaxial CaF2 layer grown on an n+-Si substrate was used as the insulator in a metal–insulator–semiconductor cathode with a 10 μm2 emitter region. The fabricated cathodes exhibited two different types of I–V characteristics. The first type showed conventional tunnel emission current of 22 pA at an emitter current of 2.4 mA and an emitter voltage of 7 V. The emitter with the other type of characteristics showed an emission current of 5.6 nA at an emitter current of 2.2 mA and an emitter voltage of 4.5 V but it showed current instability.