Ph.D Thesis


Ph.D StudentYotam Gil
SubjectCurrent-Voltage Relations and Point Defect Distribution in
Mixed-Ionic-Electronic-Conductors
DepartmentDepartment of Physics
Supervisors Professor Emeritus Riess Ilan
Professor Tsur Yoed
Full Thesis textFull thesis text - English Version


Abstract

The electronic properties of a device based on mixed-ionic-electronic-conductor (MIEC) between two inert metal electrodes, are investigated. The MIEC is assumed to be a p-type semiconductor with mobile acceptors. Another model is considered in which the acceptors are immobile, but electron hopping is allowed between charged and neutral acceptor sites. In addition steady state and one-dimensional geometry are assumed. In the MIEC model, the electrodes block the ionic current. The models are solved numerically. The solutions for the two models consist of the point defect distribution profile, the electric field profile and the current-voltage relations. Different electrodes, sample thicknesses, number of grain boundaries, mobilities and recombination times are considered. An analytical solution is presented in the limit of thin samples.

The motion of the acceptors is found, in some cases, to introduce only minor changes in the I-V relations. This finding may be of significance for solid state devices of reduced scale. The I-V relations of samples much thicker than the equilibrium Debye length reduce to the ones obtained assuming local neutrality throughout the sample. The analytic approximation in the limit of thin samples, suggests that the effects of ionic motion are negligible in this limit. This implies that for very thin samples dopants need not be limited only to those which exhibit low diffusion constants. It is found that the introduction of grain boundaries affects significantly the defect concentration for thick samples and has some effect on in the I-V relations, but it is found that the I-V relations are dictated mainly by the boundary conditions. When considering the hopping model instead of the MIEC model, a similar behavior is observed under most conditions (similar -V relations and behavior of the space charge).

We conclude with a set of preliminary experimental results. Here cuprous oxide film is thermally grown from a copper foil under different oxidation temperatures. Different oxide thicknesses are produced. Observing the thickness change with time during oxidation yields the chemical diffusion constant of copper through the oxide Cu2O layer. Then, the current-voltage relations of the film are measured using different voltage scan rates. In some cases the I-V relations show a dependence on the scan rate, this implies that ionic motion occurred.