Towards understanding the origin of threshold voltage instability of AlGaN/GaN MIS-HEMTs

GaN-power HEMTs with insulated gate structure suffer from threshold voltage drifts (ΔVth) under forward gate bias stress. We present a systematical approach to characterize the phenomenon and understand the dominant physical mechanisms causing this effect. We found out that ΔVth is caused by traps with a broad distribution of trapping and emission time constants. This distribution is analyzed using so called Capture Emission Time (CET) maps known from the study of bias temperature instability (BTI) in CMOS devices. Physical models, which could explain the broad distribution of time constants, are discussed.