Growth and doping of CVD diamond films
The extreme properties of diamond combined with the emergence of chemical vapour deposition (CVD) techniques for the growth of large area free standing diamond wafers has led to considerable interest in the use of this material for electronic applications. However, to date, the polycrystalline nature of the material grown by heteroepitaxy has hindered progress in this field leading to only niche applications for diamond electronics being identified. Whilst homoepitaxial growth seemed to be a solution to counter this issue, the substrate cost and the lack of a suitable dopant for -type conductivity together with the relatively large activation energy of p-type dopants reduced the effectiveness of electronic devices made from diamond. Finally, the low growth rates using standard microwave CVD techniques remains a problem. This thesis presents electronic characterisation of such homoepitaxial films using Hall effect measurements. The observation of p-type character of the surface conductivity due to hydrogen termination was confirmed and a correlation between the transport properties and the film thickness was demonstrated. In addition to Hall effect measurements, SEM/STM data are presented and the parameters for high growth rates of these overlayers are revealed. Passivation of these layers has also been investigated so that the p-type character and hence the device operation is not lost at higher temperatures when the devices are operated in air. A newly developed material, ultrananocrystalline diamond (UNCD), has been studied for its -type character. Hall effect measurements revealed the conductivity of this material is strongly influenced by the addition of nitrogen into the source gases and UNCD becomes conductive with low thermal activation energy. Finally, impedance spectroscopy measurements were taken on both UNCD and phosphorus doped material to investigate the conduction paths in both materials that lead to the -type conductivity observed in both kind of materials. The likely impact of the realisation of more effective processes for both growth and doping, described here, for the development of electronic devices from diamond is discussed.