Thermionic Field Emission in the Lifetime Estimation of p-GaN Gate HEMTs

The current transport mechanism at metal gate/p-GaN interface in p-GaN HETMs has been investigated. Space Charge Limited Current (SCLC) well describes the behaviour of current density (J(G)) at lower applied bias (V (G)<6 V), while Thermionic Field Emission (TFE) represents the dominant current mechanism at higher V-G. Then, p-GaN gate reliability was investigated by time-to-failure (TTF) analysis carried out at constant positive V-G. In particular, the devices' lifetime as function of the applied V-G was described considering the J(G)-V-G dependence according the TFE model. In this way, a maximum V-G for 10-year lifetime (V (10years)(Gmax)) of 8.5 V has been estimated, significantly higher than that extracted by conventional E-model (7 V).