Defects within carbon-based electronic materials.

摘要

The defect states that exist within chemical vapour deposition (CVD) diamond and poly(p-phenylene vinylene) (PPV) thin films have been investigated using a range of techniques. Thermally stimulated currents (TSC) and charge-based deep level transient spectroscopy (Q-DLTS) are the main techniques used. Q-DLTS has been preferred to the most widely-used capacitance-based deep level transient spectroscopy (C-DLTS) due to the wider range of structures it allows to be investigated. The properties of both diamond and conjugated polymers, which are of interest in term of electronic applications, are first reviewed. The experimental techniques used, with an emphasis on the TSC and Q-DLTS methods, are then explained. CVD diamond, with its wide bandgap (5.5eV), is well-suited for the fabrication of deep UV photodetectors. However, "as-fabricated" devices tend to be slow and to display a significant level of extrinsic photoconductivity. Photoconductive gain, TSC and Q- DLTS measurements have been carried out in order to establish a correlation between device characteristics and defect structure of the films. Passivation treatments, leading to improved device performance, are also investigated. When the diamond surface is terminated with hydrogen p-type conductivity is observed. Defect states are thought to be involved in the formation of this p-type surface conducting layer. Q-DLTS has been used to investigate the bandgap states that arise when CVD diamond thin films are hydrogenated. Conjugated polymers are known to display good electroluminescent properties which make them suitable for the fabrication of large area, flexible, light emitting diodes. However, trapping centres, acting for instance as quenching sites, are known to reduce the electroluminescence efficiency. Q-DLTS has been applied to the study of PPV-based LEDs in order to obtain new information about the complex defect structure of these devices.