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In order to improve the performance of deep ultraviolet light-emitting diodes (UV LEDs), the effects of different electron blocking layers (EBLs) on the performance of AlxGa1-xN-based deep UV LEDs at 310 nm have been studied through a numerical simulation. The simulation results show that the adoption of EBLs is critical to improve the device performance. In comparison with a conventional structure using EBL with constant Al composition (0.7), the device structure with an Al-content graded AlxGa1-xN (from 0.9 to 0.4 in the growth direction) EBL possesses numerous advantages such as lower working voltage, higher internal quantum efficiency, and less efficiency droop under high-current injection. By detailedly analyzing the profiles of energy band diagrams, distributions of carrier concentration, and electron current density, the advantages of Al-content graded AlxGa1-xN EBL are attributed to the resulting lower resistivity, higher barrier for electron leakage, and simultaneously reduced barrier for hole injection compared with the conventional EBL with constant Al composition.

The advantages of ultraviolet light-emitting diodes (LEDs) inserted with a p-AlGaN layer, whose Al mole composition is less than that of the last barrier, between the last barrier and the electron blocking layer have been investigated by using the Crosslight APSYS programs. The results show that the output power and the internal quantum efficiency of the proposed LEDs are improved. Furthermore, the efficiency droop is also mitigated effectively. Based on the analysis of electrical and optical characteristics, these improvements are mainly attributed to the relatively higher effective barrier height against the escape of electrons and an increased hole concentration in the quantum wells by inserting a hole reservoir near the active region. In addition, the optimized Al mole composition of this inserted layer has been also studied in detail, and the optimized Al mole composition has been achieved.

The advantages of blue InGaN light-emitting diodes (LEDs) with thickness-chirped barriers in the active region have been investigated by using the Crosslight APSYS programs. The results show that the output power of the proposed LED is increased 80% and the efficiency droop is decreased from 59% in conventional LED to 28% at the current of 250 mA. Based on the analysis of electrical and optical characteristics, these improvements are mainly attributed to the change of electrostatic field in the active region by using thickness-chirped barriers. In the even-numbered barriers, the fields are increased, which gets rid of more seriously bended valence band and results in decreased barrier heights for hole transport in the active region. Furthermore, the direction of electrostatic field in the last barrier is reversed to along the drift direction of holes, which not only can lead to upbended conduction band to rise the barrier height for electron escape but also can accelerate holes to increase the hole injection current. As a result, electrons blocking and holes injection are enhanced, and in turn, the performance of the proposed LED is improved.