Band crossing in isovalent semiconductor alloys with large size mismatch: First-principles calculations of the electronic structure of Bi and N incorporated GaAs

For large size- and chemical-mismatched isovalent semiconductor alloys, such as N and Bi substitution on As sites in GaAs, isovalent defect levels or defect bands are introduced. The evolution of the defect states as a function of the alloy concentration is usually described by the popular phenomenological band anticrossing (BAC) model. Using first-principles band-structure calculations we show that at the impurity limit the N-(Bi)-induced impurity level is above (below) the conduction- (valence-) band edge of GaAs. These trends reverse at high concentration, i.e., the conduction-band edge of GaAs1-xNx becomes an N-derived state and the valence-band edge of GaAs1-xBix becomes a Bi-derived state, as expected from their band characters. We show that this band crossing phenomenon cannot be described by the popular BAC model but can be naturally explained by a simple band broadening picture.

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This work was supported by the "973" program of the National Basic Research Program of China under Grant No. G2009CB929300 and the National Natural Science Foundation of China under Grants No. 60821061 and No. 60776061. J.L. acknowledges financial support by the "One-hundred-Talent-Plan" program of the Chinese Academy of Sciences. The work at NREL was supported by the U.S. Department of Energy, under Contract No. DE-AC36-08GO28308.

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This work was supported by the "973" program of the National Basic Research Program of China under Grant No. G2009CB929300 and the National Natural Science Foundation of China under Grants No. 60821061 and No. 60776061. J.L. acknowledges financial support by the "One-hundred-Talent-Plan" program of the Chinese Academy of Sciences. The work at NREL was supported by the U.S. Department of Energy, under Contract No. DE-AC36-08GO28308.