Field emission from ZnO whiskers under intervalley electron redistribution

ZnO field-emitter whiskers with nanometer diameter were fabricated by metal-organic chemical vapor deposition (MOCVD) growth on Si substrates. Their electron field emission properties and electron transfer effect between the valleys were investigated in a high vacuum chamber. The Fowler-Nordheim (F-N) plots of the emission current show different slopes for the small and high electric field regions. A model based on the electron-emission from valleys having different specific electron affinities is proposed to explain the experimental results. The paper presents a study of the conduction band of nano-structured ZnO with the help of field emission experiments. The energy difference between the lower and upper valleys was determined to be between 3.02 eV and 3.3 eV. The effective work function from the satellite valley is much lower than from the Γ-valley. These results can explain the usually obtained large discrepancies between extremely high field enhancement factors by fitting using F-N equation with known work function Φ from the Γ-valley and the geometrical estimated field enhancement factors for ZnO emitter. These functional field emitters based on ZnO materials and their ternaries can also be used as ultraviolet photodetector and find new applications for miniaturized photo-field assisted vacuum devices.

► Study of the conduction band of nano-structured ZnO whiskers. ► Electron transfer effect between the conduction band valleys in ZnO. ► Very low electron affinity from upper valley. ► Model for explanation of unusually large field enhancement factors for ZnO emitter.