Study on the charging current of surface traps in AlGaN/GaN high electron mobility transistors with a slot gate structure

Abstract

The charging current of surface traps in AlGaN/GaN high electron mobility transistors with a slot gate structure was investigated. A slot was formed in the middle of the gate metal via the lift-off process. Even though the slot gate only partially controlled the channel, the transient drain current gradually decreased toward a saturated off-state value with increasing measurement time after application of an off-state gate voltage. This indicated that the slot gate was still capable of turning off the entire channel. Analysis of the experimental results indicated that electrons were injected from the gate and trapped in the slot region, resulting in the depletion of the slot channel. An equivalent charging current by the surface traps on AlGaN could be inferred via the charge conservation principle. Temperature-dependent measurements of the charging current showed that it could be well fitted by the Poole-Frenkel conduction mechanism, with an extracted trap energy level of 0.129 eV.