Mechanism of Buffer-Related Current Collapse in AlGaN/GaN HEMT

摘要

Current collapse, as one of the most important factors that affect the characteristics of AlGaN/GaN HEMTs has studied for long, but there is still no uniform conclusion on its mechanism. Transient pulse method and DC method are employed to analyze the dependence of current collapse on buffer layer trap based on numerical simulation. The transient pulse simulation shows that, during the negative part of RF cycle, a large number of channel electrons(2DEG) at the gate edge of the drain side are trapped by buffer layer traps, which is dependent on the high electric field intensity. When the RF waveform on its positive half cycle, the electric field intensity under the gate edge of the drain side is reduced and the buffer layer trap begin to emit the trapped electrons. However, due to the slower emission rate, the density of the 2DEG cannot be fully recovered before the next half of RF cycle. That's the reason why the output current is scaled smaller in transient condition than it is in DC condition. The DC simulation suggests that hot electrons influence the charge transport by spilling over into the bulk GaN where they are captured by traps. It leads to negative differential conductivity in the output characteristics.