Nitrides Seminar - Jimmy-Xuan Shen, Graduate Student Researcher

2/23/2017 12PM ESB 1001


Shockley-Read-Hall (SRH) recombination is the process by which electrons and holes recombine near an atomic defect/impurity while emitting their energy as phonons instead of photons.  Recently, experimental work [1] at UCSB discovered that MBE GaN grown at UCSB and other laboratories around the world systematically contains high (up to ~1E18 /cm3) levels of unintentional calcium (Ca) incorporation.  Such high concentrations of an impurity can lead to a large SRH recombination coefficient (A) which can dramatically compromise the efficiency of light-emitting devices.  Using hybrid functional first-principles calculations we assess the role of Ca impurities in GaN [2].  Ca substituted on the cation site acts as a deep acceptor with a level ~1eV above the GaN valence-band maximum.  We also compute SRH coefficients due to multi-phonon emission of the substitutional Ca impurity. We find that for Ca concentrations of 1E17 /cm3, the SRH recombination coefficient, A, in InGaN exceeds 1E6 s-1 for band gaps less than 2.5 eV.  A coefficients of this magnitude can lead to significant reductions in the efficiency of LEDs.

[1] Young, E.C., Grandjean, N., Mates, T.E. and Speck, J.S., Applied Physics Letters109(21), p.212103 (2016)

[2] Shen, J.X., Wickramaratne, D., Dreyer, C.E., Alkauskas, A., Young, E., Speck, J.S. and Van de Walle, C.G., Applied Physics Express10(2), p.021001. (2017)