AlGaN/GaN high electron mobility transistors (HEMTs) showed its promising features in high power and high frequency applications such as inverter units in hybrid electric vehicles, advanced radar systems, and satellite-based communication networks with its high density of sheet carrier concentration, high electron mobility, and radiation hardness. However, intrinsic defects and impurities in the channel and gate-to-drain regions degrades HEMT performance through phenomena such as drain current collapse, high gate leakage, and lower rf power efficiency. Moreover, subsequent electrical stressing of the HEMTs during operation leads to creation of more traps and further device degradation through various mechanisms, including gate contact sinking, shallow trap formations, and the inverse piezoelectric effect. It is clearly desirable to have non-destructive methods available that can identify the activation energies and spatial location of trap states in GaN-based heterostructure devices.

              In this work, a sub-bandgap optical pumping technique using 671, 532 and 447 nm lasers was used to determine the trap locations in AlGaN/GaN HEMTs. Using different photon fluxes, the traps with different activation energies can be identified. This indicates that the defects originated at different physical locations in the HEMT heterostructures. The locations of the traps were confirmed by companion gate pulse measurements under optical pumping.