Observation of Hot Electron Field Emission

Abstract

We report energy distributions of silicon Field Emitter Arrays coated with 50A of ZnO. The distributions reflect changes in the ZnO conductivity induced by annealing in vacuum, temperature, and annealing in hydrogen. An additional coating of titanium performed in-situ produced large additional changes. Emission from the ZnO at energies near the Fermi level increased with gate voltage only after hydrogen annealing, when hot, and after Ti coating. In those same cases the emission distribution contained a tail at energies above E_F. The highenergy emission tail is due to a many-body or Auger process whereby holes injected below E_F create hot electrons. Although emission from ZnO occurred at energies up to 8eV below E_F, no high-energy tail was observed in the normal case. Thus emission appears to occur from isolated electrons in ZnO gap states in cases where the distribution lacks a high-energy tail. Conversely, emission above E_F suggests that emission occurred from a metallic state such as an accumulated conduction band.