Trap detection in electrically stressed AlGaN/GaN HEMTs using optical pumping

AlGaN/GaN High Electron Mobility Transistors (HEMTs) with gate lengths of 0.14–0.17 μm were electrically stressed under on-state (VG = 0 V), off-state (VG = −5 V) and typical operating conditions (VG = −2 V) and subsequently illuminated with below band-gap light to monitor changes in drain current corresponding to the changes in trapping and de-trapping of carriers within the band-gap. The changes in drain current are indicators of a change in trap density as a result of electrical stressing, since the energy from a specific wavelength of light fills traps whose activation energies are less than or equal to that of the light source. Changes in trap densities were minimal after both off-state and on-state stressing but significant trap creation in the range EC-0.4–0.6 eV were observed in HEMTs exhibiting gradual degradation during stressing. Energy levels corresponding to these values in the literature have been suggested to correlate with GaN and NGa substitutional defects, as well as GaI interstitials.