Field Emission Properties Of Several Wide Band Gap Semiconductor Materials

As the human-machine information exchange interface, the display plays a vital role in modern information society. The widely applied cathode ray tube (CRT) display works under high voltages and it is very energy-consuming. It is also incompatible with the fabrication technology of integration circuits and difficult to be miniaturized. The CRT display technology therefore needs to be replaced. The field emission-based display (FED) does not need the scanning of electron beams and has the advantages of reduced thickness, low energy consuming, high resolution, large area display with high stability, etc. So it is the most promising display of the next generation.Though much progress has been made about FE panel display technology, the technology is still far from large scale application. The major problems are due to the lack of the materials with the desired field emission properties and that much remains to be resolved about the available field emission materials including their fabrication and properties etc. Therefore, the research about field emission materials has recently attracted much attention in the area of material research.In recent years, researchers have been keeping exploring new materials with fine field emission properties. These materials have almost all the desired properties required by the field emission cathode materials, such as good chemical and thermal stability, high melting point and thermal conductivity, low diaelectric, high electron mobility and high breakdown voltage. In particular, the electron affinity (EA) of these materials is very small and some even have negative electron affinity (NEA), which makes them to be promising field emission materials.In this thesis, several wide band gap materials were fabricated and their field emission properties were researched. The fabrication and properties of these materials were summarized as follows:(1) Diamond like carbon (DLC) films and amorphous CN_X (a-CN_x) filmsElectrochemical deposition was used to grow these films. The effect of deposition voltage, temperature and time on the deposition current density was researched for DLC films. For a-CN_x films, the effect of deposition voltage on the deposition current density was investigated. It is found that higher voltage and temperature favors the growth of DLC films while higher voltage also favors the growth of a-CN_x films. The structural and FE properties of the films grown with the optimized conditions were measured, and it reveals that DLC films have better FE properties than a-CN_x films, due to the puffy or loose structure of a-CN_x films, the rougher surface and wider band gap of DLC films.(2) Amorphous GaN thin filmsDC sputtering was used to deposit amorphous GaN (a-GaN) thin films. The structure of the film, the effect of H₂ plasma treatment and Si doping on the FE properties of the films, and the mechanism for the variation of the FE properties were all studied. After the H₂ plasma treatment, the protrusions of the surface were reduced and the defect density states of the a-GaN were reduced. Some protrusions of the films were even etched away and the surface got smoothed. All these weakened the FE properties of the films. Si doping enables the electrons in the defect band to be directly emitted to the vacuum. It possibly also leads to and hence enhances the FE properties.(3) GaN nanowires, InGaN nanowires and InN nanowiresAll these nanowires were fabricated by chemical vapor deposition (CVD). The influence of the growth temperature, gas flow rates and growth time on the morphology was studied. The structure and FE properties of the nanowires fabricated with the optimized conditions were also investigated. GaN nanowires grown at 950℃with the NH₃/Ar ratio of 1/2.5 are hexagonal. The field emission current density of GaN nanowires is the largest because of larger emission site density and the absence field screen effect. InGaN nanowires grown at 600℃for 70 min withour Ar are of a mixture of cubic and hexagonal phases with different In compositions. These InGaN nanowires have the smallest turn-on field and the largest current density. InN nanowires grow at 550℃without Ar are also of a mixture of cubic and hexagonal phases and these InN nanowires have the smallest turn-on field and the largest current density.(4)HfN_xO_ythin filmHfN_xO_y thin films were fabricated by DC sputtering. The influence of the annealing temperature on the structure and field emission properties was studied, and the FE mechanism was also discussed. With the increase of the annealing temperature, the composition of the film was changed, as indicated by the decrease of HfN and the increase of HfO₂. The increase of the annealing temperature also increases the grain size of the film. With the increase of the annealing temperature, surface protrusions or cone like protrusions of nano scale were observed. Because of the structural, compositional and morphological change, HfN_xO_ythin films annealed at 800℃have the smallest turn-on electric field and the largest current density.The study of the FE properties of the above wide band gap materials enriched the experimental data about FE research, and also provided experimental evidence in understanding unclear FE mechanism.