Dynamics of surface electron trapping of a GaN-based transistors revealed by spatiotemporally resolved x-ray spectroscopy

Gallium nitride (GaN)-based transistors are promising for realizing ultralow latency of wireless information communications that are indispensable for smart societies. However, surface states have slow time constants of (de)trapping electrons and delay electrical signal responses of the transistors, which prevent the ultralow latency. To clarify the mechanism of surface electron trapping (SET) of GaN-based transistors, which varies spatiotemporally, we studied the dynamics of the SET by using spatiotemporally resolved x-ray spectroscopy. We directly observed that neutralization of donor-like surface states occurs only near the gate edge in the drain side just after switching off the bias. We found that the large local electric field formed by the bias application induces site- and time-specificity in the SET, which leads to the delayed responses. Our proposed mechanism will be useful for optimizing the transistor structure to achieve the ultralow latency.