Failure mode for p-GaN gates under forward gate stress with varying Mg concentration

In this work we investigate the failure modes of GaN based e-mode transistors with a p-GaN gate, for which the top contact towards the p-GaN is realized with a Schottky metal. First the general performance and stability of the platform will be demonstrated, together with the time dependent dielectric breakdown (TDDB) behavior of the gate. The failure mechanism of the gate has been studied by performing constant voltage stress (CVS) measurements. This has been performed for two different process conditions with varying active Mg concentration. Main results in this paper demonstrate i. Reliable device operation for p-GaN gates with Schottky metal contacts II. TDDB degradation of the gate driven by a percolation path III. The type of percolation path is dependent on the gate processing. Results indicate the formation of a percolation path in the AlGaN barrier, which is demonstrated by experiments and further verified by modelling.