Determination of the Reliability of AlGaN/GaN HEMTs through Trap Detection Using Optical Pumping

Abstract

When illuminated with below band-gap light, the response of the drain current of AlGaN/GaN High Electron Mobility Transistors (HEMTs) was measured. The energy of the wavelength of light corresponds to the trapping and de-trapping of carriers within the band-gap, providing an indicator of trap densities. These changes were compared on HEMTs with gate lengths of 0.14 & 0.17 μm, before and after electrically stressing under on-state (VG = 0 V), off-state (VG =-5 V), and typical operating conditions (VG = -2V) indicating a change in trap density as a result of electrical stressing, since the energy from a specific wavelength of light pumps 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 GaN and NGa substitutional defects, as well as GaI interstitials.