High-electric-field-stress-induced degradation of SiN passivated AlGaN/GaN high electron mobility transistors

AlGaN/GaN high electron mobility transistors (HEMTs) are fabricated by employing SiN passivation, this paper investigates the degradation due to the high-electric-field stress. After the stress, a recoverable degradation has been found, consisting of the decrease of saturation drain current I_\rm Dsat, maximal transconductance g_\rm m, and the positive shift of threshold voltage V_\rm TH at high drain-source voltage V_\rm DS. The high-electric-field stress degrades the electric characteristics of AlGaN/GaN HEMTs because the high field increases the electron trapping at the surface and in AlGaN barrier layer. The SiN passivation of AlGaN/GaN HEMTs decreases the surface trapping and 2DEG depletion a little during the high-electric-field stress. After the hot carrier stress with V_\rm DS=20 V and V_\rm GS=0 V applied to the device for 10^4 sec, the SiN passivation decreases the stress-induced degradation of I_\rm Dsat from 36% to 30%. Both on-state and pulse-state stresses produce comparative decrease of I_\rm Dsat, which shows that although the passivation is effective in suppressing electron trapping in surface states, it does not protect the device from high-electric-field degradation in nature. So passivation in conjunction with other technological solutions like cap layer, prepassivation surface treatments, or field-plate gate to weaken high-electric-field degradation should be adopted.