Negative electron affinity of diamond and its application to high voltage vacuum power switches

This paper reviews the electron emission properties of hydrogen terminated diamond surfaces with a negative electron affinity (NEA), and presents the recent development of 10 kV vacuum switches based on diamond PIN junction electron emitters that utilize such NEA surfaces. The background to this topic, including the electron emission mechanism through NEA, the electronic states of diamond with free excitons, and free carrier injection from a heavily doped layer with hopping conduction into a high purity intrinsic layer with band conduction, is also discussed. Our 10 kV vacuum power switch featuring an NEA diamond PIN junction electron emitter exhibited a breakthrough power transmission efficiency of 73% at 9.8 kV. This result validates the principle of such vacuum power switches, which have the potential to operate at 100 kV with an efficiency beyond 99.9%.