Key candidates for efficient power conversion for high voltage applications are electronic devices based on aluminium nitride (AlN), gallium nitride (GaN) and their alloys. Traditionally, a lateral high electron mobility transistor (HEMT) structure is used, in which a two-dimensional electron gas is formed by polarization-induced band bending at the interface between a strained AlGaN film and a GaN buffer. Such HEMT devices work well for applications requiring a voltage up to 650V, but at higher voltages it is difficult to achieve the desired performance due to surface traps. Furthermore, high voltages require larger devices and a greater active area on the chips, which can be seen as inviable from both an economic and a manufacturing standpoint. Therefore, for these applications there is a shift towards using vertical devices that adopt a field effect transistor structure. These are anticipated to provide a higher breakdown voltage and a larger current that carries capacity within a more compact footprint.
With a background in Chemical Engineering and Material Science, I joined the Cambridge Centre for Gallium Nitride in Autumn 2024 as a PhD student. My project is part of a larger effort working on the development of vertical gallium-nitride-on-silicon transistor devices. I will be looking specifically at the microstructure of these devices with the aim to analyse and control the defects and strain, which can potentially impair the functionality of the devices.
