Dynamics of Charge Trapping in GaN/AlGaN/GaN High Electron Mobility Transistors Grown by Plasma Assisted Molecular Beam Epitaxy

We report on the dynmaics of trapped charge in unpassivated GaN/AlGaN/GaN high electron mobility transistors grown by plasma-assisted molecular beam epitaxy. Trap states are probed using a transient channel current technique. By tailoring the gate pulse depth and width, this method allows selective probing of different trapping centers. We have identified at least two different trap centers that influence the current dynamics in our structures. In addition, the charge emission from the traps is found to have a clear square root dependence on the applied electric field. This unambiguous field dependence allows us to isolate the mechanisms responsible for emission. We estimate the characteristic time required to fill available trap states and a lower bound for the trap density.