Electrical characterization of InGaN/GaN light emitting diodes grown by molecular beam epitaxy

We studied the electrical behavior of multiple InGaN/GaN quantum well based light emitting diodes grown by molecular beam epitaxy and we determined three different domains of current-voltage dependence. We then described the charge carrier transport mechanisms for these three domains. The first domain, corresponding to leakage currents (V<1.5 V), takes place in the mesa side wall, in a semi-insulating material formed by air contamination, after the etching process. Below room temperature, electrical transport occurs by hopping between localized states and above room temperature by the Poole-Frenkel mechanism. The second domain, that of injection currents (1.5 V<V<3.5 V), corresponds to a hole injection from the valence band of p-GaN to the first InGaN quantum well. At low temperature (T<250 K) this hole injection is due to tunnel transfer and above 250 K to thermoionic emission. In the third domain, which corresponds to series resistor (V>3.5 V), the current is limited by the p-GaN zone. In this zone, the density of the free holes is controlled by the combined effects of the temperature and the applied forward bias. The results obtained enables the electronic states resulting from the magnesium doping to be localized at 190 meV above the valence band maximum. (C) 2003 American Institute of Physics.