A yellow band electroluminescence characteristic, which could be attributed to the same origin as yellow luminescence defects, was observed in GaN high electron mobility transistors (HEMT) at room temperature. The yellow luminescence-like defect origin was tentatively confirmed by comparing electroluminescence and photoluminescence results. To explore further the properties of yellow luminescence-like electroluminescence centers, the dependence of the latter upon the drain-to-source and gate-to-source voltage was investigated. A direct comparison of the electroluminescence and temperature distribution images from the same GaN HEMT suggested that 2 distinct electroluminescence emission mechanisms existed at the off-state breakdown. The other type of electroluminescence emission at off-state was attributed to carrier intravalley transition due to hot carrier generation by impact ionization at localized breakdown sites. The yellow luminescence-like emission was shown to have a stronger electric field than the hot carrier induced emission.

Observing Electroluminescence from Yellow Luminescence-Like Defects in GaN High Electron Mobility Transistors. H.Chen, Z.Lai, S.C.Kung, R.M.Penner, Y.C.Chou, R.Lai, M.Wojtowicz, G.P.Li: Japanese Journal of Applied Physics, 2008, 47, 3336-9