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

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 (V_G = 0 V), off-state (V_G =-5 V), and typical operating conditions (V_G = -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 E_C=-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 Ga_N and N_Ga substitutional defects, as well as Ga_I interstitials.