On the origin of enhanced hole injection for AlGaN-based deep ultraviolet light-emitting diodes with AlN insertion...

For the [0001] oriented AlGaN-based deep ultraviolet light-emitting diodes (DUV LEDs), the holes in the p-type electron blocking layer (p-EBL) are depleted due to the polarization induced positive sheet charges at the last quantum barrier (LQB)/p-EBL interface. The hole depletion effect significantly reduces the hole injection capability across the p-EBL. In this work, we propose inserting a thin AlN layer between the LQB and the p-EBL, which can generate the hole accumulation at the AlN/p-EBL interface. Meanwhile, the holes can obtain the energy when traveling from the p-EBL into the multiple quantum wells (MQWs) by intraband tunneling through the thin AlN layer. As a result, the hole injection and the external quantum efficiency (EQE) have been remarkably enhanced. Moreover, we point out that the thick AlN insertion layer can further generate the hole accumulation in the p-EBL and increase the hole energy which helps to increase the hole injection. We also prove that the intraband tunneling for holes across the thick AlN insertion layer is facilitated by using the optimized structure.