Space charge and quantum effects on electron emission

Abstract

Space charge effects reduce electron emission by altering the surface barrier via two effects: increasing the barrier height (Schottky factor) and width to electron emission by lowering the surface field and changing the magnitude of the dipole associated with electron density variation. A one-dimensional emission model using a transit time argument to account for charge in the anode-cathode (AK) gap and an analytical model of the dipole is used to approximate the effects of each factor on the current density. The transit time model is compared to the experimental data of Longo [J. Appl. Phys. 94, 6966 (2003)] for thermal emission. Changes in the dipole contribution are primarily associated with tunneling and therefore field emission. The transit time plus dipole modification is compared to the experimental data of Barbour [Phys. Rev. 92, 45 (1953)] for field emission. The model's application to thermal-field, and photoemission in general is discussed, with the former corresponding to continuous current limit and the latter to a pulsed current limit of the model. © 2012 American Institute of Physics.