Band-Gap Nonlinearity in Lead Chalcogenide ( PbQ, Q = Te, Se, S) Alloys
Narrow band-gap lead chalcogenides have been developed for several optical and electronic applications. However, band-gap energies of the ternary and quaternary alloys have received little attention compared with the parent binary phases. Here, we have fabricated single-phase ternary (PbTe)1−x(PbSe)x and quaternary (PbTe)0.9−y(PbSe)0.1(PbS)y and (PbTe)0.65−z(PbSe)0.35(PbS)z alloys and shown that although lattice parameters follow Vegard's law as a function of composition, the bandgap energies exhibit a substantial bowing effect. The ternary (PbTe)1−x(PbSe)x system features a smaller bowing parameter predominantly due to the difference in electronegativity between Se and Te, whereas the larger bowing parameters in quaternary alloys are generated from a larger crystal lattice mismatch and larger miscibility gap. These findings can lead to further advances in tuning the band-gap and lattice parameters for optical and electronic applications of lead chalcogenides.