Reliability of GaN high-electron-mobility transistors: state of the art and perspectives

Failure modes and mechanisms of AlGaN/GaN High Electron Mobility Transistors are reviewed. Data from three DC accelerated tests are presented, which demonstrate a closecorrelation between failure modes and bias point. Maximum degradation was found in “semion” conditions, close to the maximum of hot electron generation which was detected with theaid of electroluminescence measurements. This suggests a contribution of hot-electron effects to device degradation, at least at moderate drain bias (Vds < 30 V). A procedure for the characterization of hot carrier phenomena based on electroluminescence microscopy and spectroscopy is described. At high drain bias (Vds> 30 V - 50 V) new failure mechanisms are triggered, which induce an increase of gate leakage current. The latter is possibly related with the inverse piezoelectric effect leading to defect generation due to strain relaxation, and/or to localized permanent breakdown of the AlGaN barrier layer.Results are compared with literature data throughout the text.