Current transport and emission mechanisms in high-brightness green InGaN/AlGaN/GaN single-quantum-well light-emitting diodes

We have studied electroluminescence and photoluminescence for Nichia single-quantum-well Al0.2Ga0.8N/In0.45Ga0.55N/GaN green light-emitting diodes over a broad range of temperatures and currents. The most striking behavior is an anomalous temperature shift of both photo- and electroluminescence, with the emission peak moving towards higher energies with increasing temperature. This blue shift is opposite to that of the energy gap of the active layer, which practically excludes standard interband transitions as responsible for the observed optical transitions. We have also observed a very large blue shift of the emission peak with the increased current. This shift is an order of magnitude larger than one might expect from calculations of the conduction band filling. We show that the observed anomaly can be accounted for within the framework of the band tail model. In addition, our measurements of temperature-dependent voltage-current characteristics show that electrical transport through the p-n junction in these devices is dominated by carrier tunneling, which seems to be omnipresent in GaN-based optoelectronic devices.