Heteroepitaxial Growth of GaN on Diamond Substrates with High Thermal Conductivity

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Since breakthroughs in the growth of single crystal GaN films in the 1980s, the direct bandgap semiconductor GaN has become one of the most important semiconductors for industrial applications. Without it, the development of the nowadays ubiquitous light-emitting diode would have been unfeasible. But GaN is not only interesting for the application in light emitting diodes but also in power electronic devices, especially for devices with high operating frequency. However, at high power densities these devices are reaching certain limitations. The insufficient heat transport form the active device region limits their maximum power density. To increase the power density or the reliability of these devices it would be favourable to improve the heat transport. The aim of this project is to achieve this by directly growing GaN onto diamond substrates. In the first part of the project GaN films will be grown on single crystal diamond substrates to determine the optimum growth conditions. As even synthetic diamond single crystals are expensive, and thus only of interest for specific applications, the second and most important part of the project aims at growing single crystal GaN films on polycrystalline diamond films. Achieving this goal will require to influence the nucleation of the GaN in such a way that GaN nuclei only form on diamond crystallites with the same orientation by pretreating the diamond films and choosing appropriate growth conditions. Subsequently the GaN nuclei will coalesce into a closed single crystal film. In the third, and last, part of the project the scalability of the developed process will be demonstrated. The process will be transferred to 6” or 8” Si-wafers that are coated with polycrystalline diamond films.