Influence of low temperature p-GaN layer on the optical properties of a GaN-based blue light-emitting diodes

The optical properties of two different InGaN/GaN multiple-quantum-well (MQW) light-emitting diodes (LED), without, and with, a low-temperature (LT) p-GaN layer, were studied by using electroluminescence (EL) methods assisted by photoluminescence (PL) methods. The measurement results show that inserting an LT p-GaN layer between the MQW active region and the p-AlGaN electron block layer (EBL) can prevent the re-evaporation of In in the MQW active region, particularly in the last QW, since the sample with an LT p-GaN layer shows a obvious red-shift of the EL peak and a enhanced localisation effect of the carriers inferred from the more obvious "S-shaped" temperature dependent behaviour of the peak energy. Meanwhile, the introduction of the LT p-GaN layer also results in a great increase in the integrated EL intensity and a significant reduction in the efficiency droop. This is mainly attributed to the improvement of the hole injection efficiency and the suppression of the electron leakage. In addition, it may be also related to the enhanced localisation effect, the reduced QCSE, and the improved crystal quality of the MQW active region and p-type region, due to the introduction of the LT p-GaN layer.