Reverse gate bias stress induced degradation of GaN HEMT

GaN High Electron Mobility Transistors (HEMTs) represent the most attractive, and perhaps viable, solution for tackling the needs of high power and high efficiency microwave and millimeterwave power amplifiers. Their impressive capability of manage power levels which are tenths times higher than those achieved by other semiconductor devices has been demonstrated by various authors. Nevertheless, there is a strong need of investigating their long term reliability due to the relative commercial immaturity of this semiconductor technology. Decrease in output power and power added efficiency as a consequence of device knee-walkout and gate current degradation are amongst the most deleterious effects that can arise during device operation. We have shown that high reverse biases can result in the formation of defects located at the drain edge of the gate contact. These defects have been related with the increase in both reverse currents, as well as the device current-collapse. Recently we have also shown that devices subjected to an electrical step stress by reverse biasing the gate Schottky junction experienced a decrease in the DC drain current level, correlated with current-collapse and an increase in the current-DLTS signals which yielded an activation energy of 0.5eV,