NUSOD Blog

Connecting Theory and Practice in Optoelectronics

NUSOD 2017 Preview: Maximum GaN-laser power limited by Auger recombination

AugerT80Auger recombination inside the light-emitting InGaN quantum wells (QWs) was recently identified as major cause of output power limitations in GaN-based blue light-emitting diodes (LEDs) which are the core of many modern light sources. In this electron-hole recombination process, the released energy is transferred to another carrier (electron or hole) without light emission. The Auger recombination rate rises strongly with the QW carrier density and therefore intensifies with stronger current injection into the LED.

In contrast to LEDs, GaN-based blue laser diodes are expected to suffer less from Auger recombination,  based on the popular opinion that the QW carrier density does not rise with increasing current injection above lasing threshold. Shuji Nakamura, who received the 2014 Nobel Prize in physics for his pioneering work on GaN-LEDs, stated in his Nobel lecture that “Auger recombina­tion, with the resulting efficiency droop, does not appreciably occur in blue laser diodes”.  We dispute this claim based on our numerical analysis of  high-power InGaN/GaN laser measurements.

As discussed previously on this blog, the QW carrier density rises due to the self-heating of the laser diode with increasing current injection. This triggers enhanced carrier losses which divert more of the injected current away from the stimulated photon emission which generates the laser beam. Our analysis reveals the current components that feed carrier loss mechanisms such as Auger recombination, electron leakage from the QWs, spontaneous photon emission, and defect-related non-radiative recombination (see picture). Auger recombination causes the largest carrier loss in this laser. At high current, it even overwhelms the stimulated photon emission and thereby limits the maximum lasing power.

More details will be presented at the NUSOD 2017 conference in Copenhagen (paper TuB2).

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