The performance of nitride-based LEDs was improved by inserting dual stage and step stage InGaN/GaN strain relief layer (SRL) between the active layer and n-GaN template. The influences of step stage InGaN/GaN SRL on the structure, electrical and optical characteristics of GaN-based LEDs were investigated. The analysis of strain effect on recombination rate based k·p method indicated 12.5% reduction of strain in InGaN/GaN MQWs by inserting SRL with step stage InGaN/GaN structures. The surface morphology was improved and a smaller blue shift in the electroluminescence (EL) spectral with increasing injection current was observed for LEDs with step stage SRL compared with conventional LEDs. The output power of LEDs operating at 20 mA was about 15.3 mW, increased by more than 108% by using step stage InGaN/GaN SRL, which shows great potential of such InGaN/GaN SRL in modulating InGaN/GaN MQWs optical properties based on its strain relief function.

The degradation mechanism of high power InGaN/GaN blue light emitting diodes (LEDs) is investigated in this paper. The LED samples were stressed at room temperature under 350-mA injection current for about 400 h. The light output power of the LEDs decreased by 35% during the first 100 h and then remained almost unchanged, and the reverse current at −5 V increased from 10 −9 A to 10 −7 A during the aging process. The power law, whose meaning was re-illustrated by the improved rate equation, was used to analyze the light output power-injection current (L-I) curves. The analysis results indicate that nonradiative recombination, Auger recombination, and the third-order term of carriers overflow increase during the aging process, all of which may be important reasons for the degradation of LEDs. Besides, simulating L-I curves with the improved rate equation reveal that higher-than-third-order terms of carriers overflow may not be the main degradation mechanism, because they change slightly when the LED is stressed.

To improve the electrostatic discharge properties of InGaN/GaN LEDs, an n + -InGaN electron injection layer and a p-InGaN/GaN hole injection layer were inserted beneath and above the InGaN/GaN MQWs. The influences of activated donor concentration in n + -InGaN and acceptor concentration in p-InGaN/GaN and on the depletion width and the internal capacitance of GaN-based n + -P LED have been investigated. Our research results indicated that the capacitance of GaN-based n + -P LED is mainly determined by the depletion width which is dependent on the activated acceptor concentration N A in the p-InGaN/GaN hole injection layer. The relationship between the internal capacitance of InGaN-LEDs and the electrostatic discharge (ESD) properties was also investigated. It was found that the LEDs with large internal capacitance were more resistant to external ESD impulses. With optimized LED structures with n + -InGaN layer and a p-InGaN/GaN SLs, the HBM-ESD pass yield at −1500 V reached 95%, much higher than the value of 15% in reference samples without inserting layers above.