Surface transfer doping of diamond using transition metal oxides

This thesis presents a body of work which advances the use of single crystal hydrogen terminated diamond as a semiconducting material. Surface transfer doping of intrinsic diamond is investigated, examining the current state of this technology and its limitations. New techniques for producing robust, thermally stable surface transfer doped diamond were achieved through use of transition metal oxides such as MoO3 and V2O5, as demonstrated experimentally by way of Hall measurement. Through use of these materials, thermal stability was greatly increased up to temperatures of at least 300oC. To achieve this higher temperature operation, encapsulation of MoO3 and V2O5 was found to be necessary in maintaining conductivity of the diamond surface due to suspected thermally-induced loss of hydrogen termination. Similarly, long term atmospheric stability is shown to necessitate annealing of the diamond surface prior to oxide deposition and for thinner layers of oxide, down to 10 nm, encapsulation of the oxide to isolate from atmosphere is shown to be required for increased stability. As well as the improvements in stability offered by these transition metal oxides, sheet resistance of the hydrogen terminated diamond surface was also greatly reduced. Carrier densities as high as ~7.5 ×1013 cm-2 were observed for MoO3-induced surface transfer doping, resulting in a low sheet resistance of ~ 3 kΩ/□. In parallel to the development of oxide acceptor materials, conditioning of the diamond surface was explored using Atomic Force Microscopy (AFM). Techniques for smoothing the surface after mechanical polishing were developed by way of RIE and ICP etching using both chlorine and oxygen mixtures. Surface roughness down to 2 angstroms was demonstrated, showing a significant improvement in roughness over mechanical polishing alone. Similarly, observed defects produced by polishing induced damage were removed through use of this etching strategy. The effects of varied plasma density during hydrogen termination was explored on etched surfaces, which produced higher quality hydrogen-terminated surfaces as verified by surface conductivity and AFM measurements. Finally, incorporation of MoO3 into a preliminary Field Effect Transistor (FET) device on diamond was attempted. Fabrication techniques to produce a FET device on hydrogen-terminated diamond is shown with preliminary results of MoO3 encapsulated devices. Insights into the fabrication of ohmic and gate contacts, incorporating MoO3, is also discussed