Current Saturation in Nonmetallic Field Emitters

It has been known for a long time that traditional semiconductor (e.g. intrinsic and doped Si and Ge or binary SiC and GaN) field emitters significantly deviate from Fowler-Nordheim (FN) law and saturate when a large current, on the order of microamperes or more, is attempted to be drawn from them. Many experiments established that the field emission current from carbonic materials, such as carbon nanotubes, amorphous carbon and polycrystalline diamond films, also deviate from FN law and saturate. These findings suggested that the saturation and departure from FN law is a broad and general phenomenon that applies to the class of nonmetallic field emitters. In this letter, we report a universal formula that describes the current saturation effect in nonmetallic field emitters. The formula accounts for material's bulk properties and field emitter geometry.