Secondary electron emission and conductivity mechanisms of epitaxial MgO films

Abstract

Secondary electron emission and electron bombardment induced conductivity measurements have been made on epitaxial MgO films (50–200 Å thick) deposited on a (100)Mo substrate. The films were deposited and measurements made under UHV conditions. Changes in the sample surface potential ( V s) were determined from changes in the threshold energy of the secondary emission energy distribution, thus allowing current ( I) versus V s curves to be made. It was found that the conductivity data could be fitted best by a Poole-Frenkel conductivity mechanism. Mechanisms for electron injection from the substrate into the film were not consistent with the data, implying that holes are the dominant charge carriers. This is in contrast to most results on polycrystalline MgO films which conclude that electron tunneling is probably dominant in such films. The possible ways that these differences in conduction mechanisms can affect processes that degrade the secondary emission properties of these films are discussed.