High breakdown voltage and low on-state resistance make AlGaN/GaN High Electron Mobility Transistors (HEMTs) very attractive for switching applications. However, because to its strong piezoelectric effect the conventional GaN HEMT structure is unsuitable for enhancement-mode (E-Mode) operation, which is usually required to improve the safety of the switching systems. In this work we present a GaN HEMT, where a gate recess in combination with Metal Insulator Semiconductor (MIS) structure have been used to obtain a positive threshold voltage (VTH). Insulator layer effectively helps to reduce the parasitic gate leakage currents, but unfortunately MIS-HEMT devices suffer of threshold voltage instability due to the charge trapping that occurs in the insulator layer [1,2,3]. Our aim is to investigate the trapping mechanisms in MIS-HEMT structure exploiting different characterization techniques
