In this work, the different nature of trapping states in metal-oxide-semiconductor (MOS) capacitors fabricated on recessed AlGaN/GaN heterostructures has been investigated. In particular, the origin of both fast and slow states has been elucidated by frequency dependent conductance measurements. Using post deposition annealing in forming gas, which is known to induce hydrogen incorporation at the interface, allowed to ascribe the fast traps (with characteristic response time in the range of 5–50 μs) to SiO2/GaN interface states and the slow traps (50–100 μs) to “border traps” located few nanometers inside the SiO2 layer. The results can be useful to predict the behavior of GaN switching devices, like hybrid MOSHEMTs.
