Influence of p-GaN annealing on the optical and electrical properties of InGaN/GaN MQW LEDs

Optical and electrical properties of InGaN/GaN multiple quantum wells (MQWs) light emitting diodes (LEDs) annealed in pure O₂ ambient (500 C) and pure N₂ ambient (800 C) were systematically investigated. The temperature-dependent photoluminescence measurements showed that high-temperature thermal annealing in N₂ ambient can induce indium clusters in InGaN MQWs. Although the deep traps induced by indium clusters can act as localized centers for carriers, there are many more dislocations out of the trap centers due to high-temperature annealing. As a result, the radiative efficiency of the sample annealed in N₂ ambient was lower than that annealed in O₂ ambient at room temperature. Electrical measurements demonstrated that the LEDs annealed in O₂ ambient were featured by a lower forward voltage and there was an increase of ~41% in wall-plug efficiency at 20 mA in comparison with the LEDs annealed in N₂ ambient. It is thus concluded that activation of the Mg-doped p-GaN layer should be carried out at a low-temperature O₂ ambient so as to obtain LEDs with better performance.