Heteroepitaxial Growth of GaN on Diamond Substrates with High Thermal Conductivity

自20世纪80年代单晶GaN薄膜生长取得突破以来，直接带隙半导体GaN已成为工业应用中最重要的半导体之一。如果没有它，现在无处不在的发光二极管的发展将是不可行的。但是GaN不仅在发光二极管中的应用是令人感兴趣的，而且在电力电子器件中也是令人感兴趣的，特别是对于具有高工作频率的器件。然而，在高功率密度下，这些器件正达到某些限制。来自有源器件区域的不充分的热传输限制了它们的最大功率密度。为了增加这些装置的功率密度或可靠性，改善热传输将是有利的。该项目的目的是通过在金刚石衬底上直接生长GaN来实现这一目标。在项目的第一部分，GaN薄膜将在单晶金刚石衬底上生长，以确定最佳生长条件。由于即使是合成金刚石单晶也很昂贵，因此只对特定应用感兴趣，该项目的第二个也是最重要的部分旨在在多晶金刚石薄膜上生长单晶GaN薄膜。实现这一目标将需要通过预处理金刚石膜和选择适当的生长条件来影响GaN的成核，使得GaN核仅在具有相同取向的金刚石微晶上形成。随后GaN核将聚结成封闭的单晶膜。在第三，也是最后，项目的一部分，开发过程的可扩展性将被证明。这一过程将转移到6”或8”Si晶片上，这些晶片涂有多晶金刚石膜。

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.