On the polarization effect of the p-EBL/p-AlGaN/p-GaN structure for AlGaN-based deep-ultraviolet light-emitting diodes

The external quantum efficiency (EQE) and light output power (LOP) for III-nitride based deep ultraviolet light-emitting diodes (DUV LEDs) are strongly influenced by the hole injection efficiency. This work shows that the hole concentration in the active region is strongly subject to the polarization level of the p-region that consists of the p-type electron blocking layer (p-EBL), the p-AlGaN and the p-GaN layers. The hole injection becomes poor once the p-EBL/p-AlGaN and p-AlGaN/p-GaN interfaces are of the [000-1] polarity. On the contrary, the improved hole injection can be obtained once the polarization level that is of the [0001] polarity for the p-EBL/p-AlGaN and p-AlGaN/p-GaN interfaces increases. The increased polarization level of the [0001] polarity can not only reduce the hole depletion within the p-AlGaN layer, increase the energy for the holes, but also reduce the valence band barrier height of the p-EBL for holes, which in turn facilitates the hole injection capability and enhances the EQE for DUV LEDs.