9 April 2010 - Semiconductor Today
April 9, 2010 Tunneling a way to understand the efficiency of InGaN LED droop
Researchers based in St. Petersburg, Russia, have turned their attention to the static efficiency of light emission electric current in the nitride semiconductor light emitting diodes [Bochkarev NI et al, Appl. Phys. Lett., Vol96, p133502, 2010]. Collaboration suggests a mechanism involving static tunneling leakage of carriers in quantum well (QW) to a defect in the states barriers and a reduction in the carrier injection efficiency by an excess tunneling current between deep defect states in the barriers , bypassing the QW (Figure 1).The work consisted of AF Ioffe Physico-Technical Institute, St. Petersburg Polytechnic University and VF Fock Institute of Physics.
As evidence of tunneling mechanisms related, the researchers cite three experimental results of their work: the static efficiency is in the low energy spectrum of photon emission, the forward voltage droop when the efficiency is in (~ 2.9V) is independent of temperature (77-300k), and tension than before the voltage peak efficiency, the ideality factor diode is higher than 2 (4.4 to 300K) .
An ideality factor greater than 2 can be a signal to Auger recombination, which is one of the most popular explanations for the effects of static efficiency nitride LEDs. "Auger recombination" refers to a mechanism where the energy from a recombination event is given to another carrier, rather than being emitted as light, thereby reducing the emission light output. Since Auger recombination involves three carriers, it should occur at higher currents.
In opposition to such an explanation, researchers at St. Petersburg point to a reduction of peak current efficiency at low temperature (0.47mA at 300K, at 90K 7μA) and comment: "This decline in efficiency at low currents can hardly be attributed to Auger recombination....
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Figure 1: St. Petersburg defect-related tunneling model for a pn structure with an AlGaN/InGaN/GaN QW. As the potential difference between the injection
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