Avoiding avalanche breakdown in planar GaN Gunn diodes by means of a substrate contact

Abstract

Impact ionization originated by the buffer leakage current, together with high electric fields (> 3 MV/cm) at the anode corner of the isolating trenches, has been identified as the failure mechanism of shaped planar GaN Gunn diodes when biased above 20V, so that no evidence of Gunn oscillations in fabricated devices has been observed yet. In order to avoid the avalanche, we propose the addition of a Schottky substrate terminal, which, by means of Monte Carlo simulations, has been confirmed to be able to suppress such not-desired leakage current when applying a negative substrate bias. When the substrate bias is positive, impact ionization is also reduced due to the lower electric field at the hotspot, but a vertical cathode-substrate current degrades the device operation. In order to avoid such current, we propose the use a MIS configuration for the substrate contact, which is the optimal solution.