Equivalent-Circuit Analysis for the Electroluminescence-Efficiency Problem of InGaN/GaN Light-Emitting Diodes

Electroluminescence (EL) efficiency of the InGaN-based light-emitting diode (LED) is the present subject of discussion. An equivalent circuit model was introduced to treat explicitly four independent current components: leakage, radiative, nonradiative, and carrier overflow. This model was used to explain the internal quantum efficiency (IQE) as a function of current, temperature, and material quality. In the low-current range, efficiency became strongly dependent on temperature as leakage and nonradiative recombination currents related to material quality shared a large part of the total current. In the high-current range, the reduced efficiency was explained by electron-overflow current. Electron-overflow current was increased by reducing temperature via freeze-out of holes. When leakage current and carrier overflow were suppressed effectively in the intermediate current range on high-quality devices, hole freeze-out was observed experimentally in electroluminescence intensity as temperature was varied.