Gallium nitride (GaN) based materials have excellent figures of merit for high power, high frequency and high temperature devices. Transistors consisting of an aluminium gallium nitride (AlGaN) barrier layer grown on GaN have been studied extensively as ideal candidates for this purpose for both civilian and defence applications. The advantages of the nitride material system for such applications stem from their large band gap, large breakdown field, and the polarisation fields which induce a two-dimensional electron gas (2DEG) with high electron concentration at the hetero-interface. To date, these III-nitride systems have achieved impressive performance metrics such as over a ten-fold increase in power density over competing gallium arsenide (GaAs) based counterparts.

We are investigating two new types GaN-based transistors. Instead of using an AlGaN barrier, an aluminium nitride (AlN) barrier is being investigated in one approach, while a lattice matched indium aluminium nitride (InAlN) barrier is under investigation in another approach. Theoretical calculations indicate that these structures can achieve much higher electron concentrations at the hetero-interface compared to the existing AlGaN/GaN technologies (over 200% improvement). This is expected to translate into even higher microwave power densities or higher current handling capability. The motivation for investigating the InAlN/GaN heterostructure is also related to the ability to grow InAlN lattice matched to GaN (i.e. without strain) but still achieve high electron concentration (2DEG) at the hetero-interface. Unstrained structures are thought to be free of issues such as current collapse which still compromise the performance of AlGaN/GaN devices. The AlN barrier devices, on the other hand, are easier to design for enhancement-mode operation and so would be better suited for switching (power electronics) applications.

For further information contact DR. Edward Wasige – e.wasige@elec.gla.ac.uk