(Invited) Unraveling the Efficiency Limits of GaN-Based Emitters and the Surprising Connection to Electron Devices

In this talk, we review our recent experiments designed to reveal the fundamental efficiency limits of GaN-based LEDs:  (i) electroemission spectroscopy studies of InGaN-based LEDs with cesiated surfaces provide the first direct measurement of Auger electrons that result from an electron-electron-hole (eeh) Auger process.  Auger-generated electrons survive transit through the p-GaN by transfer to a low lying side valley.  The relationship between the observation of Auger electrons and the onset of droop provides compelling evidence that the internal Auger process is the dominant droop mechanisms [1]; (ii) related above gap photoemission studies on p-GaN with cesiated surfaces demonstrate a low level side conduction band valley (nominally referred to as “L”) ~0.9 eV above Γ [2]; (iii) atom probe tomography studies on InGaN-based LEDs demonstrate that the indium alloy follows a binomial distribution, as expected for a random alloy.  2D drift-diffusion simulations show that the alloy fluctuations are essential to explain the low turn-on voltages of InGaN-based LEDs [3];  (iv)  vertical carrier transport studies on majority carrier analogs to LEDs, namely all n-type InGaN/GaN MQWs  and GaN/AlGaN/GaN structures confirm the importance of natural alloy fluctuations in vertical transport [4,5].

[1]  J. Iveland et al., Phys Rev. Lett. 110, 177406 (2013)

[2]  M. Piccardo et al., Phys. Rev. B, in press (2014)

[3]  Y.-R. Wu et al., Appl. Phys. Lett. 101, 083505 (2012)

[4]  D. Browne et al., in preparation (2014)

[5]  M. Fireman et al., in preparation (2014)