[INVITED] Special AlGaN graded superlattice hole and electron blocking layers improved performance of AlGaN-based ultraviolet light-emitting diodes

In order to improve the electrical and optical performance of ultraviolet light emitting diodes (UV-LEDs), Al0.65Ga0.35N/AlxGa1-xN graded superlattice hole blocking layers (GS-HBLs) and Al0.65Ga0.35N/AlxGa1-xN graded superlattice electron blocking layers (GS-EBLs) are applied to the traditional AlGaN-based UV-LEDs. Compared to conventional structure, our new structure can obtain much higher internal quantum efficiency (IQE), output power and lower efficiency droop. In order to reveal the underlying physical mechanism of this unique structure, we have studied it numerically by the Advance Physical Model of Semiconductor Devices (APSYS) simulator. We find that GS-EBLs can obviously increase the electron potential height and reduce the hole potential height, produce less electron leakage and more hole injection, leading to higher carriers concentration. GS-HBLs can obviously reduce the hole leakage, reduce the thermal velocity and correspondingly the mean free path of the hot electrons, and increase the electron injection. This enhanced the electron capture efficiency of the multiple quantum wells, which can also help to reduce electron leakage and improve recombination rate and IQE.