Today, it is widely accepted that the large auger coefficient is the main reason for the large (~50%) efficiency degradation in conventional hexagonal-phase InGaAlN LEDs. Nevertheless, this explanation is insufficient to account for the low efficiency observed in gallium arsenide- and gallium phosphide-based LEDs, as they have similar Auger coefficients.
in IEEE Transactions on Electron DevicesCain Bayram, Jean-Pierre Laborton and Yi-Chia Tsai at the University of Illinois at Urbana-Champaign show that the coexistence of strong internal polarization and large carrier effective mass results in a ~51% reduction in efficiency under high current densities in hexagonal crystals. -phase green InGaAlN LEDs (h-LEDs) compared to cubic-phase InGaAlN green LEDs (c-LEDs).
Previously, the efficiency reduction in non-polar H-LED was attributed to a reduction in carrier leakage from the active region, given the interplay between internal polarization and auger recombination. Indeed, recent experiments suggest that the efficiency reduction in non-polar H-LEDs is actually due to carrier delocalization, (a different situation from polar H-LEDs) resulting in stronger electron-hole wavefunction overlap, lower quantum well carrier from. density, and low auger recombination rates. The team found that larger carriers promote effective mass carrier localization and degrade the band-to-band optical transition matrix element.
According to this new interpretation, the researchers show that switching from a polar H-LED to a C-LED results in a 45% to 22% (i.e. 51%) reduction in efficiency due to polarization elimination and a reduction in effective mass. It is further found that the quantum efficiency of Si-LEDs is highly immune to the mechanisms of auger electron-hole asymmetry, enhancement of the auger coefficient, and thus efficiency degradation. Therefore, cubic-phase InGaAlN green LEDs provide a suitable solution to quench the reduction in efficiency.
Yi-Cia Tsai et al, Quenching of the efficiency drop in cubic phase InGaAlN light-emitting diodes, IEEE Transactions on Electron Devices (2022). DOI: 10.1109/ted.2022.3167645
Going cubic reduces efficiency in InGaAlN light emitting diodes (2022, April 27).
Retrieved 27 April 2022
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