Beschreibung
Defect-assisted nonradiative recombination via trap-assisted Auger
F. Zhao, M. E. Turiansky, C. G. Van de Walle*
Materials Department, University of California, Santa Barbara, USA
*email: vandewalle@mrl.ucsb.edu
Defect-assisted nonradiative recombination is still a key mechanism limiting the efficiency of nitride optoelectronic devices. First-principles calculations have been instrumental in elucidating the fundamental processes [1] and identifying detrimental defects in InGaN active layers emitting at green wavelengths [2,3]. It has been challenging, however, to identify defect-related sources of loss in wider-band-gap materials emitting in the blue or ultraviolet. The rate of defect-assisted recombination via multiphonon emission strongly decreases as the energy difference between the defect level and the band gap increases, and since a nonradiative recombination cycle requires sequential capture of both an electron (from the conduction band) and a hole (from the valence band), the rate of one of these processes becomes negligibly low in wider-band-gap materials. Experimentally, however, defect-assisted recombination is observed to persist at larger band gaps [4]. This puzzle can be resolved by taking into account trap-assisted Auger recombination [5]. Similar to band-to-band Auger recombination, a trap-assisted Auger process enables capture by exciting a carrier to a higher-energy state.
We have developed a practical first-principles methodology to determine the trap-assisted Auger recombination rate for defects and impurities in semiconductors. As a test case, we focused on a calcium substitutional impurity [3,4]. For band gaps larger than 2.5 eV, the combination of hole capture by multiphonon emission and electron capture by trap-assisted Auger results in recombination rates orders of magnitude larger than the recombination rate governed by multiphonon emission alone. Our computational formalism is general and can be applied to any defect or impurity in any semiconducting or insulating material.
References
[1] A. Alkauskas, Q. Yan, and C. G. Van de Walle, Phys. Rev. B 90, 075202 (2014).
[2] C. E. Dreyer, A. Alkauskas, J. L. Lyons, J. S. Speck, and C. G. Van de Walle, Appl. Phys. Lett. 108, 141101 (2016).
[3] J.-X Shen, D. Wickramaratne, C. E. Dreyer, A. Alkauskas, E. Young, J. S. Speck, C. G. Van de Walle, Appl. Phys. Express 10, 021001 (2017).
[4] E. Young, N. Grandjean, T. Mates, and J. Speck, Appl. Phys. Lett. 109, 212103 (2016).
[5] A. C. Espenlaub, D. J. Myers, E. C. Young, S. Marcinkevičius, C.Weisbuch, and J. S. Speck, J. Appl. Phys. 126, 184502 (2019).