Defect-mediated charge transport in semiconducting structures based on copper oxide

Abstract

This thesis report presents a study performed on the physical properties of cuprous oxide thin films and their use, such as light emitting diode, solar cell, and so on. Precisely, an experimental study on the defects in the film based on a metal-semiconductor structure is made. Then, solar cells using gallium oxide and copper oxide are simulated to optimize solar efficiency. The work comprises 4 parts, detailed as follows:

Firstly, a theoretical background in the science of semiconductors, junctions, and solar cells, as well as a state of the art of both cuprous oxide and gallium oxide are introduced. The availability and the sustainability of the studied materials are briefly commented on.

Then, the tools used for the thin film deposition are explained with their characteristic results. The films are fabricated with varying annealing processes. Their electrical properties are measured, giving low resistivity and low hole mobility. Then, silver contacts are deposited on the cuprous oxide films with the perspective of observing a rectifying current-voltage curve.

The following part introduces tungsten contact as an alternative to silver. The metallic contact is made via the needle of a probe station. Although the interface exhibits natural variability which does not lead to the expected Schottky diode behavior, it is straightforward to implement and produces a non-ohmic response to an applied DC voltage. A space-charge-limited current model is applied to the measured tungsten-cuprous oxide diodes. The resulting analysis shows the relevance of such an approach for the understanding of the charge transport mechanism in the fabricated interface.

The last part focuses on the modeling of the solar cell gallium oxide-cuprous oxide. In this perspective, the use of the Scaps software is validated via theoretical comparison with the classical silicon pn junction. Then, the junction is optimized in a parametrical study with film thicknesses and doping levels as variables of interest. The process is made for both pristine and defective cells. Subsequently, an additional AZO layer is with the aim of solar efficiency enhancement.