X-ray spectroscopic studies of the electronic structure of chromium based p-type transparent conducting oxides

Abstract

In this thesis the electronic, optical, electrical, and mechanical properties of two p-type transparent conducting oxides will be explored, primarily by spectroscopic techniques. The initial chapters outline how the properties of high optical transparency and electrical conductivity can co-exist in a material. The most industrially relevant subset of these materials, n-type transparent conducting oxides, are pervasive in optoelectronics. The p-type counterparts suffer from inferior properties. Two of these p-type transparent conducting oxides were analysed by a variety of spectroscopic techniques: x-ray absorption spectroscopy, x-ray photoelectron spectroscopy and resonant photoemission spectroscopy. The consensus from this spectroscopic analysis led the author to conclude that the origin of the low mobility within chromium based oxides is due to the presence of the common element chromium. Studies on a novel p-type oxide nanocrystalline CuxCrO2 indicated the highly conductive nature of the films is linked to the presence of copper vacancies within the material. Despite the low mobility of some p-type oxides they have found applications within electronic devices. An experimental technique that can probe the energy band alignment of two materials will reveal that Cr2−xMgxO3 has the appropriate energy band alignment with the anode ITO in an organic solar cell to be an efficient selective contact for the extraction of holes from the cell. It also reveals that the room temperature deposition of Cr2−xMgxO3 and ZnO creates a rectifying diode but a large amount of defect states exist at the interface, creating a high ideality factor of all the diodes manufactured within this work. Finally, the resilience of copper deficient CuCrO2 to mechanical strain shows it has promise as a large area transparent flexible electrode.