Power limitation due to premature breakdown in in AlGaN/GaN HFETs

A systematic investigation of high field prebreakdown and breakdown phenomena of AlGaN/GaN Heterojunction Field Effect Transistors (HFETs) is presented. The breakdown process was studied as a function of various parameters such as applied electric field, material layer structure. semiconductor surface conditions, ambient dielectric, and test conditions. Experimental evidence of a breakdown mechanism, distinct from the bulk/subsurface breakdown, namely on-surface breakdown or surface flashover is presented. A practical, unambiguous way of identifying device failure by surface flashover is proposed. Surface flashover between gate and drain contact edges is proposed as the main mechanism initiating premature breakdown in these devices leading to a significant reduction of their power capability.