Shockley-Read-Hall recombination affects electroluminescence efficiency in gallium nitride LEDs

The peak efficiency of gallium nitride light emitting diodes (LEDs) is largely determined by the concentration of deep traps. However, in these materials it was not clear which deep centers mainly contribute to non-radiative Shockley-Read-Hall (SRH) recombination. Reporting in the Journal of Applied Physics, a group of Russian, Korean and American researchers developed approaches to determine the parameters of deep traps in III-Nitride LEDs and examined how the traps affect electroluminescence efficiency in blue LEDs compared to different LED materials.

Electron radiation was used to increase the concentration of deep traps in the LED structures. Co-author, Alexander Polyakov, explained that they overcame problems related to the large band gap, high ionization energy of Mg acceptors in the p-region, and the difficulty in accessing the active region for measurements. The solution involved performing measurements at lower frequencies, optimizing the forward bias and pulsing conditions, and applying light excitation to characterize hole traps with levels near the middle of the gap.

Polyakov explained that they found an increase in concentration of certain types of deep centers closely correlated with the decrease of electroluminescence efficiency. The deep centers in question were traced to specific types of point defects; interestingly, these defects were further removed from the middle of the band gap than had been theoretically predicted.

With the production of III-Nitride LEDs operating in UV and green-red spectral ranges, Polyakov said that the researchers are now examining how changes in wavelength affect the characteristics of non-radiative recombination centers. They also want to develop methods to characterize rates of capture for both electrons and holes by the center of interest, something necessary for accurate calculations of SRH recombination efficiency.

Source: “Point defects controlling non-radiative recombination in GaN blue light emitting diodes: Insights from radiation damage experiments,” by In-Hwan Lee, A. Y. Polyakov, N. B. Smirnov, I. V. Shchemerov, P. B. Lagov, R. A. Zinov’ev, E. B. Yakimov, K. D. Shcherbachev, and S. J. Pearton, Journal of Applied Physics (2017). The article can be accessed at https://doi.org/10.1063/1.5000956 .