关键词: AlGaN/GaN high electron mobility transistors, surface states, traps in AlGaN, passivation

Abstract: 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.

Key words: AlGaN/GaN high electron mobility transistors, surface states, traps in AlGaN, passivation