Articles you may be interested inWe performed, for the first time, quantitative characterization of electron capture cross sections r of the interface states at dielectric/III-N heterojunction interfaces. We developed a new method, which is based on the photo-assisted capacitance-voltage measurements using photon energies below the semiconductor band gap. The analysis was carried out for AlGaN/GaN metal-insulatorsemiconductor heterojunction (MISH) structures with Al 2 O 3 , SiO 2 , or SiN films as insulator deposited on the AlGaN layers with Al content (x) varying over a wide range of values. Additionally, we also investigated an Al 2 O 3 /InAlN/GaN MISH structure. Prior to insulator deposition, the AlGaN and InAlN surfaces were subjected to different treatments. We found that r for all these structures lies in the range between 5 Â 10 À19 and 10 À16 cm 2 . Furthermore, we revealed that r for dielectric/ Al x Ga 1Àx N interfaces increases with increasing x. We showed that both the multiphonon-emission and cascade processes can explain the obtained results. Published by AIP Publishing.