Study On GaN-Based Vertical-structure Light Emitting Diode With Coupled Quantum Wells

Compared with Ga N-based conventional light-emitting diodes(LEDs) chips, Ga N-based vertical-structure LEDs(VS-LEDs) chips which solve the current crowding effects and poor heat dissipation, are more suitable for high-power LEDs at high current injection. However, Ga N-based LEDs suffer from efficiency droop under high current injection level. It plays an important role for improving VS-LEDs chips by solving efficiency droop.Based on the problem of non-uniform carriers distribution in conventio nal In Ga N/Ga N multiple quantum wells(MQWs) structure, seven 2D models of Ga N-based VS-LED chips with varied number of CQWs were building by APSYS simulation software. The simulated results showed that CQWs improve hole uniform distribution in In Ga N/Ga N MQ Ws, and the radiative recombination.The simulated results also indicate that, when the number of CQWs was not more than 5, with the number of CQWs increasing Ga N-based VS-LED chips models had better and better properties such as radiative recombination, forward voltage and light-output power. When the number of CQWs was more than 5, the properties of Ga N-based VS-LED chips models were not much better than that with 5 CQWs. Ga N-based VS-LED chips models with 5 CQWs had better properties, comparing with the model just with normal quantum wells(NQWs), wherein forward voltage reduced by 0.46 V and light-output power increased by 39.4%, at the injected current of 350 m A.Based on the simulated results, the Ga N-Base VS-LED chip sample with 5 CQWs was fabricated by MOCVD, the laser lift-off and electroplating techniques. Compared to Ga N-Base VS-LED chip sample only with NQWs, the VS-LEDs with CQWs had better properties, wherein forward voltage reduced by 0.68 V and light-output power increased by 53.0% at a forward current of 350 m A. Meanwhile, the relative external quantum efficiencies of VS-LEDs with NQWs and CQWs were reduced to 37.7% and 67.5% of their maximum, respectively. The result revealed that the efficiency droop of LEDs could become less severe. Through discussing EL spectrum, it was analyzed that the reason why efficiency droop of LEDs with CQWs was solved at high current injection level. It plays an important role in application of high-power LEDs chips to general illumination.