3D Concepts for Gallium-Nitride Electronics

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Electronic devices based on Gallium Nitride (GaN) are nowadays regularly used as High Electron Mobility Transistors (HEMTs), e.g. in mobile communication. Due to its high breakdown voltage of 3 MV/cm and potentially high operating temperatures, GaN is also more and more intensely discussed for future power electronics in the intermediate voltage range. The further development of GaN electronics in general, and in particular for power electronics, is generally seen to be hampered by various issues, including too high defect densities, too low transient power dissipation capability and limited breakdown behavior. Vertical device geometries (e.g. in IGBTs), which have been proven to be extremely useful in power electronics, are not available, which is due to missing GaN high quality bulk substrates. GaN FET technology today is relying on a planar HEMT approach, relying on a 2-dim electron gas at the AlGaN-GaN interface. The main idea of our project is to explore a vertical concept for GaN electronics based on 3D GaN nanorods. In fact, 3D GaN nanorods would have the potential to overcome most of the above mentioned limitations of planar 2D HEMT technology and could lead to a completely new type of GaN electronics later on, when many of the existing foundational questions have been answered. The concept of this project is to explore the potential of 3-dimensional GaN (GaN nanorods) as a basis for novel vertical electronic GaN-based devices, with a particular emphasize - but not exclusively - on power electronics. The project is based on substantial progress in the two participating groups at TU Braunschweig and Uni Kassel over the last years concerning the reproducible MOVPE growth of GaN 3D micro- and nanorods, with large area homogenous fabrication of nanorod ensembles on 2 inch and 4 inch substrates, as well as an advanced theoretical understanding of the properties of such 3D GaN nanowires. In summary, the project aims at the exploration and development of central process and device strategies for a future vertical GaN MOSFET technology. Such vertical design concepts will allow straight forward scaling towards large area devices (by using e.g. millions of nanoFETs in parallel with vertical current path) potentially carrying (and switching) very large currents. Also, parallel vertical 3D device geometries would allow for more efficient cooling strategies. Overall, our vertical device strategy addresses many of the issues being identified as serious challenges in planar GaN power devices. A particularly important aspect of this project will be the combination of experimental and theoretical expertise in the field of 3D GaN.