The influence of nitride heterostructures on efficiency droop is presented. It was developed a special method based on simulation for investigating the changes in the semiconductor devices characteristics due to different influencing factors. The cause of efficiency droop was detected - large difference in carrier lifetimes. The simulation results are used to suggest several ways for improving LED efficiency about 12 %.
Blue and green LEDs have been simulated. Changing LED performance characteristics, depending on In concentration
and at different temperatures were simulated. It was suggested that a LED having p-n junction area S0 can be considered
as a sum of "SmallLEDs (SLEDs)" electrically connected in parallel, each SLED has its own In-content and its own p-n
junction area S(X). Values of ratio S(X)/S0 are described by Gauss distribution function in the range X = 0.15-0.25 for
blue LEDs and X = 0.25-0.35 for green LEDs. Reasonable correspondence of simulation and experimental results
(current-voltage characteristic (C-V Ch), Spectral Ch) can be observed.
Light-emitting diodes (LEDs) degradation during 10 000 hours and the influence of ultrasonic action on the InGaN LEDs were investigated. The model of LED degradation is suggested and based on 1) common LED is the combination of parallel Small-LEDs (S-LED) which correspond to the areas with different concentration of In atoms; 2) redistribution
of In atoms in quantum-dimensional active region of blue InGaN LED under strong piezoelectric effect and spontaneous
polarization induced by ultrasonics; 3) the ultrasonics which is used in creating LEDs can make defects in
heterostructures and they (during LEDs work) are heated by current or ultrasonic, can be increased and that's why
nonradiation recombination decreases LEDs efficiency. It can be said that great current density flows through areas with
low In concentration and therefore S-LEDs are "burned out" and irradiate less. At the areas with average In
concentration the densities decrease. That is why electroluminescence spectrum, radiation power, luminous intensity
characteristics are shifted to the long wave region. All that also exactly corresponds with our experimental results of
LEDs degradation investigation during 10 000 hours.