Defect States Induced In Gan-Based Green Light Emitting Diodes By Electron Irradiation

The spatial distribution of deep traps in electron irradiated green multi-quantum-well (MQW) GaN/InGaN light emitting diodes was determined by deep level transient spectroscopy with electrical and optical injection. Four major electron traps with levels near Ec-0.2 eV, E-c-0.5 eV, E-c-0.75 eV, and E-c-1.1 eV were observed. The concentration of all electron traps increased with fluence of 6 MeV electrons, correlating with a decrease of the external quantum efficiency (EQE) of LEDs. The concentration of hole traps at E-v+0.45 eV also increased with irradiation. The observed EQE changes are partly attributed to trapping of electrons and holes by electron traps in the GaN barriers (E-c-0.75 eV, E-c-1.1 eV, E-v+0.95 eV) and nonradiative recombination in the QWs via electron traps E-c-0.5 eV and hole traps E-v+0.45 eV. Even traps with levels far from midgap can effectively participate in nonradiative recombination by forming close pairs similar to donor-acceptor pairs if their density is high. This can occur in In-rich fluctuation regions in the QWs, even as the densities averaged over the entire area of QWs as measured by deep level spectroscopy remain relatively low. (C) 2018 The Electrochemical Society.