Electron Emission from Thin Al-Al2O3-Au Structures

Abstract

Emitter cells with Al2O3 film thicknesses between 67 and 150 Å and Au film thicknesses between 200 and 300 Å were operated at voltages up to 10 V. Typical I-V characteristics for the total cell currents are presented. The curves suggest tunnel emission through the barrier at the Al-Al2O3 interface when the cell is operated for the first time and only small currents have been drawn. After passage of large currents, the I-V characteristics become temperature dependent. The normal energy distribution of the emitted electrons is measured and a linear dependence of the average energy on cell voltages is established. The fractions of current emitted through the Au into the vacuum is determined as a function of the Al2O3 thickness. Using the attenuation lengths of gold reported recently by Mead, an attenuation length of about 24 Å is deduced for electrons, which within the insulator have gained an energy of nearly 3 eV. The emitted current could be increased considerably by depositing a low work function material (Ba) at the gold surface. The maximum fraction of current emitted into the vacuum was 10−2, at an emitted current density of nearly 5 mA/cm2.