Time Dependent Shift in SOA Boundary and Early Breakdown of Epi-Stack in AlGaN/ GaN HEMTs Under Fast Cyclic Transient Stress

Abstract

This experimental study reports first observations of (i) SOA boundary shift in AlGaN/GaN HEMTs and (ii) early time-to-fail of vertical AlGaN/GaN epi-stack under fast changing (sub-10ns rise time) cyclic pulse transient stress, which otherwise qualified for 600 V DC stress. It is shown that a epi stack qualified for 10 years lifetime under DC stress, fails faster under cyclic transient stress. The drain-to-substrate leakage exhibits different trends under DC and pulse stress. Integrated electrical and mechanical stress characterization routine involving Raman/ PL mapping, PFM and CL spectroscopy along with atomistic simulations reveals material limited unique failure physics under transient stress condition. Failure analysis using cross-sectional SEM and TEM investigations reveal signature of different degradation and failure mechanism under transient and DC stress conditions. A failure model is proposed for rapid breakdown of AlGaN/GaN epi-stack under cyclic transient stress and it is experimentally validated.