Effects Of post-annealing on the passivation interface characteristics of AlGaN/GaN high electron mobility transistors

Abstract

We examined the effects of post-annealing in forming-gas ambient on the spin-on-dielectric (SOD)-buffered passivation as well as the conventional plasma-enhanced chemical vapor deposition (PECVD) Si3N4 passivation structure in association with the quantitative analysis of defects at the passivation interfaces of AlGaN/GaN high electron mobility transistors (HEMTs). Before the annealing, the interface state densities (D-it) of the PECVD Si3N4 are one-order higher (10(12)-10(13) cm(-2) eV(-1)) than those of the SOD SiOx (10(11)-10(12) cm(-2) eV(-1)) as derived from C-V characterization. Clear reduction in At from the PECVD Si3N4 is extracted to a level of 10(11)-10(12) cm(-2) eV(-1) with a stronger absorption from Si-N peak in Fourier transform infrared spectroscopy spectra after the post-annealing. On the other hand, negligible difference in D-it, value is obtained from the SOD Si-x. In this paper we propose that much lower measurement levels (similar to 156 mA/mm) before the annealing and substantial recovery (similar to 13% increase) after the annealing in maximum drain current density of the AlGaN/GaN HEMTs with Si3N4 passivations are due to the original higher density before the annealing and greater reduction in D-it, of the PECVD Si3N4 after the annealing. Significant reduction after the annealing in gate-drain leakage current (from similar to 10(-3) to similar to 10(-5) A, 100-mu m gate width) of the HEMTs with the Si3N4 passivation is also supposed to be attributed to the reduction of D-it. (C) 2015 Elsevier Ltd. All rights reserved.