Investigation of Inverse Piezoelectric Effect and Trap Effect in AlGaN/GaN HEMTs Under Reverse-Bias Step Stress at Cryogenic Temperature

The inverse piezoelectric effect and trap effect in GaN HEMTs under the high electric field by reverse-bias step stress at cryogenic temperature (CT, 77K) have been investigated. It is found that the inverse piezoelectric effect is suppressed while the trap effect is enhanced at CT. Due to the lower tensile stress in the as-grown AlGaN barrier at CT, the amplitude of the critical voltage related to inverse piezoelectric effect increases from 75V at 300K to 100V at CT, mitigating the irreversible degradation of the devices. The inverse piezoelectric effect dominates the degradation of reverse gate leakage, which is weakened at CT. However, the devices suffer from more degradation of Id (decreases by 94.38%) and Gm, max (decreases by 95.15%) at CT in the dark, induced by the serious trap effect due to the longer emission time. UV-light-assisted stress measurements have been utilized to identify the contribution of the two mechanisms to the degradation of device characteristics at CT. The degradation of Id(Gm, max) is only 0.82% (3.31%) for the piezoelectric effect and 93.56% (91.84%) for trap effect at CT, respectively.