Researchers from SET have identified three mechanisms that may trigger a drop in UV LEDs (below 250 nm)—the decrease in external quantum efficiency at higher current densities—that is, self-heating, load discharge (from quantum wells to blocking layers or P-type cap layer) and Auger composite.
The SET researchers concluded that comparing the continuous wave and pulse output of a strip device with different "H-pixel" and different drive currents, one can conclude that self-heating is a cause of decline. They found that the drop is not only dependent on current density, but also on the total injected current that produces Joule heat. In addition, the efficiency of the UV LEDs (pulses of 500 ns and 200 ns, 20 kHz) decreases as the current increases.
Another possible factor is the load leakage due to weak void injection, where blue shifting at high pump currents means faster inter-band filling and subsequent electron spillage into the wider bandgap material. There is also the Auger compound, which is also considered to be one of the reasons for the decline. They are considering the characterization of devices at temperatures that are not available, which may be useful for understanding more about Auger's complex effects.
In the research, the wavelength of the ultraviolet LED is between 245 and 247 nm, and the continuous wave output has a power of 2 mW. (LEDC MH compilation)
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