The Electronic Structure Of Disordered Impurities In The Sphalerite Chalcogenides Compounds

Sulfuride semiconductors with zinc-blende structure have drawn much attention as important materials for semiconductor devices and solar cell,due to their excellent opto-electronic properties.Disordered impurities and defects are important for semiconductor band structure and quantum transport properties,such as effective mass,etc.Therefore,a systematic study is needed in both theory and applications.We have systematically investigated the band structure and effective mass of disordered chalcopyrite photovoltaic materials Cu1-x Agx Ga X2(X = S,Se)by first-principles calculations based on the density functional theory,where the special quasirandom structures(SQS)method is used to mimic local atomic disorders at Cu/Ag sites in all structures.As well known,first-principles calculation will underestimate semiconductor band gap.A local density approximation plus correction(LDA+C)approach is adopted to get correct band gaps for all compounds.All transport properties are based on the corrected band structures.Our study results show that both selenides and sulfides have band-gap anormaly,where band gaps of Cu Ga X2(X = S,Se)are smaller than those of Ag Ga X2(X = S,Se).And band gaps can be modulated from 1.63 e V to 1.78 e V for Cu1-x Agx Ga Se2,and from 2.33 e V to 2.64 e V for Cu1-x Agx Ga S2.Band-gap minimum locates at around x =0.5,and the maximum at x = 1.0 for both selenides and sulfides.The detailed band structures are shown to clarify the momentum of phonon needed by the fundamental indirect-gap transitions.To understand the transport properties of Cu1-x Agx Ga X2,effective mass has been given as a function of disordered Ag concentration.At last,based on the study of the static potential and band offset,the results shown that the static potential of the semiconductors decreases by doping with Ag.The periodicity of each superlattice semiconductor of heterojunction have four in our study,who can ensure sufficiently thick of layers between adjacent interfaces.Our calculated results are useful for designing high efficiency photovoltaic devices with both better absorption and high mobility by doping with Ag in Cu Ga X2.