Applied Physics Letters 79 2339 (2001)
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The electronic and atomic structure of substitutional nitrogen pairs, triplets, and clusters in GaP and GaAs is studied using the multiband empirical pseudopotential method with atomistically relaxed supercells. A single nitrogen impurity creates a localized a1(N) gap state in GaP, but in GaAs, the state is resonant above the conduction-band minimum. We show how the interaction of multiple a1 impurity levels, for more than one nitrogen, results in a nonmonotonic relationship between energy level and impurity separation. We assign the lowest (NN1) line in GaP to a [2,2,0] oriented pair, the second (NN2) line to a triplet of nitrogen atoms, and identify the origin of a deeper observed level as an [1,1,0] oriented triplet. We also demonstrate that small nitrogen clusters readily create very deep levels in both GaP and GaAs.
Several graphics illustrating these clusters are listed on the pictures page.
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