High breakdown voltage AlGaN/GaN HEMTs on free-standing GaN substrate

In this paper we have investigated the relationship between off-state breakdown voltage and gate-to-drain distance (Lgd) for AlGaN/GaN HEMTs fabricated on a free-standing GaN substrate. The off-state breakdown voltage exhibited a linear increase up to Lgd of around 80 μm but saturated at about 4000 V when Lgd > 80 μm. Therefore, we proposed that when Lgd <; 80 μm, the breakdown voltage of HEMTs was dominated by leakage current under the channel and when Lgd > 80 μm, it was determined by the leakage current outside of the channel.