The Role of Barrier Transport and Traps in the Tradeoff Between Low OFF-State Leakage Current and Improved Dynamic Stability of AlGaN/GaN HFETs

A tradeoff behavior between low Schottky gate leakage current and improved dynamic stability of AlGaN/GaN heterostructure FETs was previously reported, and was attributed to variations in the metal/semiconductor interface properties. Here, we show that a tradeoff behavior is found in transistors and gated van der Pauw test structures that were fabricated on the same wafer, and underwent identical surface treatments. In the gated van der Pauw measurements, a slow transient response and a large variation in the 2-D electron gas concentration compared with equilibrium were detected, following a gate voltage stress in low leakage devices, but not in high leakage ones. Based upon our experimental observations, we argue that electron traps located in the AlGaN barrier layer are responsible for the tradeoff. The activation energies required to fill the empty barrier traps by electrons, obtained from the gated van der Pauw measurements, are 0.60 and 0.65 eV.