Transient measurement of GaN HEMT drift region potential in the high power state

This work reports the transient measurement of the AlGaN/GaN high electron-mobility transistor (HEMT) drift region potential in the high power state during switching. The effect of high power stress has been reported by device characterization after stress or during high power DC stress at voltages below the operating voltages to avoid device failure. However, transient measurement during high power stress is challenging, since the device can sustain the high power stress only for a few $\mu \text{s}$ before failure occurs. In this work, a test structure with voltage probe inserted in the drift region between the gate and the drain is used to perform real-time measurement of the drift region potential during the high power state at operating voltages. It is found that the high electric field formed at the gate side during the off-state stress propagates towards the drain side within a few $\mu \text{s}$ . The propagation speed of this high electric field increased with increase in drain voltage. It is proposed that trapping of hot channel electrons is causing this effect, and dynamic on-resistance measurement suggests that the traps are 0.44 eV below the conduction band.